Magnetic Materials

Magnetic Materials by Ron Kurtus (revised 11 October 2007) Materials respond differently to the force of a magnetic field. A magnet will strongly attract ferromagnetic materials, weakly attract paramagnetic materials, and weakly repel diamagnetic materials. The orientation of the spin of the electrons in an atom, the orientation of the atoms in a molecule or alloy, and the ability of domains of atoms or molecules to line up are the factors that determine how a material responds to a magnetic field. Ferromagnetic materials have the most magnetic uses. Diamagnetic materials are used in magnetic levitation and MRI. Questions you may have include: •

What are ferromagnetic materials?

•

What are paramagnetic materials?

•

What are diamagnetic materials?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator.

Ferromagnetic materials Ferromagnetic materials are strongly attracted by a magnetic force. The elements iron (Fe), nickel (Ni), cobalt (Co) and gadolinium (Gd) are such materials. (See the Periodic Table in the Chemistry section for more information.) The reasons these metals are strongly attracted are because their individual atoms have a slightly higher degree of magnetism due to their configuration of electrons, their atoms readily line up in the same magnetic direction, and the magnetic domains or groups of atoms line up more readily. (See Factors Determining Magnetic Response for more information.)

Iron and steel Iron is the most common element associated with being attracted to to a magnet. Steel is also a ferromagnetic material. It is an alloy or combination of iron and several other metals, giving it greater hardness than iron, as well as other specialized properties. Because of its hardness, steel retains magnetism longer than iron.

Permanent magnets Alloys of iron, nickel, cobalt, gadolinium and certain ceramic materials can become "permanent" magnets, such that they retain their magnetism for a long time.

Temperature effect Strongly magnetic ferromagnetic materials like nickel or steel lose all their magnetic properties if they are heated to a high enough temperature. The atoms become too excited by the heat to remain pointing in one direction for long. The temperature at which a metal loses its magnetism is called the Curie temperature, and it is different for every metal. The Curie temperature for nickel, for example, is about 350°C.

Paramagnetic materials

Paramagnetic materials are metals that are weakly attracted to magnets. Aluminum and copper are such metals. These materials can become very weak magnets, but their attractive force can only be measured with sensitive instruments. Temperature can affect the magnetic properties of a material. Paramagnetic materials like aluminum, uranium and platinum become more magnetic when they are very cold. The force of a ferromagnetic magnet is about a million times that of a magnet made with a paramagnetic material. Since the attractive force is so small, paramagnetic materials are typically considered nonmagnetic.

Diamagnetic materials Certain materials are diamagnetic, which means that when they are exposed to a strong magnetic field, they induce a weak magnetic field in the opposite direction. In other words, they weakly repel a strong magnet. Some have been used in simple levitation demonstrations.

Strongest Bismuth and carbon graphite are the strongest diamagnetic materials. They are about eight times stronger than mercury and silver. Other weaker diamagnetic materials include water, diamonds, wood and living tissue. Note that the last three items are carbon-based. The electrons in a diamagnetic material rearrange their orbits slightly creating small persistent currents, which oppose the external magnetic field.

Uses Although the forces created by diamagnetism are extremely weak--millions of times smaller than the forces between magnets and ferromagnetic materials like iron, there are some interesting uses of those materials. Levitation The most popular application of diamagnetic materials is magnetic levitation, where an object will be made to float in are above a strong magnet. Although most experiments use inert objects, researchers as the University of Nijmegen in the Netherlands demonstrated levitating a small frog in a powerful magnetic field.

Levitated Frog

MRI Another important application of diamagnetic materials is magnetic resonance imaging (MRI). In this useful diagnostic tool in medicine. The way it works is that when carbonbased atoms in the body are exposed to a strong magnetic field, they are slightly repelled by the field. This movement of the atoms can be detected and used for analysis.

Summary Magnets will strongly attract ferromagnetic materials, weakly attract paramagnetic materials, a nd weakly repel diamagnetic materials. Ferromagnetic materials have the most magnetic uses. Diamagnetic materials are used in magnetic levitation and MRI.

Factors Determining Magnetic Properties by Ron Kurtus (revised 6 October 2006) The factors that determine the magnetic property of a material are the configuration of the electrons in the material, the ability of the atoms or molecules in the material to align magnetically, and the alignment of domains or sections in the object. Since alignment is so important in the magnetic properties of materials, liquids and gases are typically not magnetic because their molecules aren't held in place as they are in solids. An exception is in rotating fluids. Questions you may have include: •

What are electron orientation factors?

•

What are molecule factors?

•

What are domain factors?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator.

Electron orientation Electrons can behave as tiny magnets, each with north (N) and south (S) poles. When an atom's electrons are lined up in the same orientation, with most having their N pole facing one direction, the atom becomes like a magnet, with N and S poles. It is also possible for the electrons to be in various directions, making the atom not magnetic.

Moving electrons create magnetic field The reason that electrons can behave like tiny magnets is the fact that when electrons move, they create a magnetic field. Placing a compass near a wire carrying DC electrical current can show that a magnetic field is created due to the electrons moving through the wire. A magnetic field is also created when electrons rotate around a nucleus and when they spin while in orbit. (Note that modern theories of the atom no longer accept the Bohr or solar system model. In the new theories, electrons are thought of as clouds or strings. You should be aware that there are new explanations, but for the sake of understanding we will still follow the Bohr model of spinning electrons rotating around a nucleus, similar to planets rotating around the Sun.)

Spinning electrons Electrons have a property called spin. This spinning creates a magnetic field with N and S poles, just as the spinning Earth has magnetic poles. Note that the N pole on an electron is really a North-seeking pole, just as in a magnet. If electrons in the shells of an atom spin in the same direction, the atom will exhibit a magnetic field and will respond to the forces of a magnet. If half of the electrons spin one way and the rest spin the other way, they will neutralize each other and the material will not be affected by a magnetic field

This atom is barely magnetic because all its electrons are not aligned

Strong and weak electron alignments Atoms such as iron have most of their electrons aligned in the same direction. Thus, iron or nickel would be attracted to a magnet. Aluminum only has a few electrons aligned, and thus it is only weakly magnetic. An element with half of its electrons oriented one way would not be attracted to a magnet.

Atomic and molecular alignment Although some atoms may be highly magnetic, they really need to be aligned to make a material magnetic. If magnetic atoms are facing different directions, their fields will cancel out each other.

Solids and fluids Since the atoms or molecules in a solid are fixed in place, most magnetic materials are solids. This is because once the atoms or molecules become aligned, they tend to stay in place. An example is seen when you magnetize a piece of iron. As a material becomes heated or when it is in its liquid or gaseous state, the atoms or molecules are in rapid motion and are not aligned. Thus, fluids are seldom magnetic. An exception is when a magnetic material such as iron is in its liquid state and is continually rotating around an axis. In such a situation, the atoms can be aligned in one direction, even though they are in rapid motion. For example, the core of the Earth is made of liquid iron. Since the Earth rotates on its axis, the liquid iron is rotating, thus creating the Earth's magnetic field. Also, the Sun rotates on its axis, and the material in its plasma state creates the Sun's magnetic field.

Molecules

If two or more elements are chemically combined to form a molecule, it is quite possible that the compound is not very magnetic because the orientations of the atoms in the molecule work against each other. A good example of this is to compare the magnetic properties of iron as compared to its compounds if iron oxide (rust) and iron sulfide. A piece of iron is highly magnetic, but a hunk of rusty iron is not.

Alloys Metals of different elements can be mixed when they are in the molten or liquid state to form alloys. These combinations result in materials with slightly different physical and chemical properties than the elements by themselves. If the metals typically respond well to a magnetic field--such as iron and nickel--then their alloy has even a stronger reaction to magnetism. On the other hand, there are some alloys of iron--such as forms of stainless steel--that do not respond well at all to a magnet.

Domains The final factor in a material being magnetic concern the orientation of its domains in a solid. A group of atoms in a metal may become aligned, but the various groups may be misaligned. These groups are called domains. It is necessary to line up many of the domains in a material like iron in order for it to become a magnet.

Magnetic material with domains misaligned

Aligned domains makes material highly magnetic

Summary Alignment of electrons, atoms and domains are important in determining the magnetic response of a material and whether it is a magnet. Since the atoms or molecules need to be aligned, gases and liquids are typically not magnetic, and most magnets are solid metals. An exception is in the rotating liquid iron core of the Earth and the rotating plasmas of the Sun.

Electromagnetism An electromagnet is an object that acts like a magnet, but its magnetic force is created and controlled by electricity--thus the name electromagnet. By wrapping insulated wire around a piece of iron and then running electrical current through the wire, the iron becomes magnetized. This happens because a magnetic field is created around a wire when it has electrical current running through it. Creating a coil of wire concentrates the field. Wrapping the wire around an iron core greatly increases the strength of the magnetic field. Questions you may have include: •

How can you make an electromagnet?

•

What factors are involved in electromagnetism?

•

How does an iron core affect the strength?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator. Note: If you want to hear the text being read, click the Play button. It takes a few seconds for the sound to start. The voices are somewhat mechanical for computer use.

Time = 7 min. 15 sec.

Making an electromagnet If you wrap a wire around an iron core, such as a nail, and you send electrical current through the wire, the nail will become highly magnetized. You can verify that by picking up small objects or by showing its effect on a compass. This is called an electromagnet.

Creating a simple electromagnet using a nail

Insulated wire Note that the wire must be an insulated wire. A bare wire would cause an electrical short and the current would then run through the nail or metal core. In some electromagnets, like in an electric motor, the wire will look like bare copper, but it is insulated with a thin coating of a clear material. Also, if the wire is thin, it may get warm from the resistance to the electricity passing through it.

Turn on and off The most interesting feature of the electromagnet is that when the electrical current is turned off, the magnetism is also turned off. This is especially true if the core is made of soft iron, which quickly loses its magnetism. Hardened steel may retain its magnetism, so you can't use the most valuable feature of an electromagnet. Being able to turn the magnetism on and off has lead to many amazing inventions and applications.

How electromagnetism works When electricity passed through a wire, a magnetic field is created around the wire. Looping the wire increases the magnetic field. Adding an iron core greatly increases the effect and creates an electromagnet. You can create an electromagnet without the iron core. That is usually called a solenoid.

Magnetic field When DC electricity is passed through a wire, a magnetic field rotates around the wire in a specific direction.

Magnetic field rotating around wire

Compass can show field Connecting a wire to a battery and placing a compass near the wire can demonstrate a magnetic field. When the current is turned on, the compass-needle will move. If you reverse the direction of the current, the needle will move in the opposite direction. Right hand rule To find the direction the magnetic field is going, you can use the "right-hand rule" to determine it. If you take your right hand and wrap it around the wire, with your thumb pointing in the direction of the electrical current (positive to negative), then your fingers are pointing in the direction of the magnetic field around the wire. Try it with the picture above.

Wire in a coil Wrapping the wire in a coil concentrates and increases the magnetic field, because the additive effect of each turn of the wire.

Coiled wire increases magnetic field

A coil of wire used to create a magnetic field is called a solenoid.

Iron core Wrapping the wire around an iron core greatly increases the magnetic field. If you put a nail in the coil in the drawing above, it would result in an electromagnet with the a north seeking pole on the "N" side.

Using AC electricity If AC electricity is used, the electromagnet has the same properties of a magnet, except that the polarity reverses with the AC cycle. Note that it is not a good idea to try to make an AC electromagnet. This is because of the high voltage in house current. Using a wire around a nail would result in a blown fuse in the AC circuit box. There is also the potential of an electric shock.

Strength of electromagnetic field The strength of the electromagnetic field is determined by the amount of current, number of coils of wire, and the distance from the wire. Unit The unit of magnetic force is called the tesla (T). Near a strong magnet the force is 1-T. Another unit used is the gauss, where 104 gauss (10,000) equals 1 tesla. Current The strength of the magnetic field is proportional to the current in the wire. If you double the current, the magnetic force is doubled. Since Voltage = Current x Resistance (V = I*R), you can double the current in a wire by doubling the voltage of the source of electricity. Turns of coil If you wrap the wire into a coil, you increase the magnetic force inside the coil, proportional to the number of turns. In other words, a coil consisting of 10 loops has 10 times the magnetic force as a single wire with the same current flowing through it. Likewise, a coil of 20 loops has 2 times the magnetic force than one with 10 loops. Varies with distance The magnetic force decreases with distance. It varies inversely proportional to the square of the distance. For example the force at 2 cm. from a wire is 1/4 that of at 1 cm., and the force at 3 cm. is 1/9 the force at 1 cm.

Effect of iron core When the coil is wrapped around an iron core, the strength of the electromagnetic field is much greater than the same coil without the iron core. This is because the atoms in the iron line up to amplify the magnetic effect. The orientation of the atoms in the iron is called its domain. Current When you increase the current, the magnetic strength increases, but it is not exactly linear as it is with the coil by itself. The characteristics of the core cause the curve of magnetic strength versus current to be an s-shaped hysteresis curve. The shape of this curve depends on how well the material in the core becomes magnetized and how long it remains magnetized. Soft iron loses its magnetism readily, while hard steel tends to retain its magnetism.

Summary By wrapping a wire around an iron core and applying an electric current through the wire, you create an electromagnet. This device is magnetic only when the current is flowing. The iron core greatly increases the magnetic strength.

Generating Electrical Current by Ron Kurtus (9 November 2003) Electrical current can be generated by moving a metal wire through a magnetic field. This applies both to alternating current (AC) and direct current (DC) electricity. This is a different method than where DC is created by a battery, which uses chemical reactions. It is also different than static electricity, which is the accumulation of charges on a surface. Electrical generators rotate a coil of wires through a magnetic field. The difference between an AC and a DC generator is that the AC generator uses slip rings to transfer the current to the electrical circuit, while the DC generator uses a split-ring commutator. Generators can be very small or quite huge. Very large ones create electricity for the community. An electric motor is very similar to a generator, except that power is provided to turn the rotors. Questions you may have include: •

What does a wire moving through a magnetic field look like?

•

How is a loop of wire used in an electric generator?

•

What do commercial generators look like?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator. Note: If you want to hear the text being read, click the Play button. It takes a few seconds for the sound to start. The voices are somewhat mechanical for computer use.

Time = 6 min. 30 sec.

Moving wire through magnetic field When a wire made of conducting material cuts through a magnetic field, an electrical current is created in the wire.

Must be part of circuit Note that the wire must be part of an electrical circuit. Otherwise the electrons have no place to go. In other words, there is no electrical current produced with a wire with open ends. But if the ends are attached to a light bulb, to an electrical meter or even to each other, the circuit is complete and electrical current is created.

Moving the wire through the magnetic field creates an electric current, as measured by a meter attached to the ends of the wire

Direction of current The direction of the magnetic field and the direction of the wire will determine the direction of the current through the wire. By convention, the direction of the magnetic field is from N to S. Also by convention, the current goes from plus (+) to minus (−). But note that in reality, the negatively charged electrons move in the opposite direction than the current. They move from (−) to (+). You'll just have to remember that the electrons move in the opposite direction than the convention for the direction of current.

Other configurations Besides moving a wire through a magnetic field, you could also create an electric current in the wire by moving the magnets and keeping the wire stationary. Another technique to create a current is to keep both stationary but vary the magnetic field. That method is used to change the voltage of AC in electrical transformers. (See AC Transformers for more information).

Loop is spun If the wire is made into a loop that is then spun or rotated in the magnetic field, you can have continuous current. Since each side of the loop is going in a different direction in the magnetic field, the current flows around the loop, depending on which direction it is rotated.

Transfer current There must also be some way to transfer the current to the rest of the circuit. In an AC generator, having a ring on each end of the wire does this. A metal contact or brush rubs or slides against each ring, allowing the electricity to flow through the circuit. In a DC generator, this is done using one split-ring called a commutator. An AC generator uses two slip rings.

Comparison of DC and AC loops and rings

Generator in action The following animation shows an AC generator in action. As one side of the loop moves to the other pole of the magnetic field, the current in it changes direction. The two slip rings of the AC generator allow the current to change directions and become alternating current.

Simple AC generator (Image from the PBS American Experience series: Inside the AC Generator)

In a DC generator, the split-ring commutator accommodates for the change in direction of the current in the loop, thus creating DC current going through the brushes and out to the circuit. Note that the DC current is not a steady value. Rather, it is a "bumpy" signal, with zero voltage at the break in the ring. The power from the current could be mathematically described as a sine wave squared. Since most DC generators have many more than one loop, the "bumps" even out and are not noticed. The faster the wire passes through the magnetic field, the greater the current.

Full-sized generators Instead of having a single loop, generators used to supply electricity to homes and businesses have multiple magnets and loops consisting of wires wound around an iron core, similar to an electromagnet. The more loops of wire passing through the magnetic field, the higher the voltage that is created.

Large generator with multiple windings

Generators used to provide electricity to the community are huge. The rotor can be well over 10 feet in diameter.

Can be used as motor Note that when a generator has its wire wound around an iron core, it can also be used as an electric motor. Instead of rotating the loops through a magnetic field to create electricity, a current is sent through the wires, creating electromagnets. The outer magnets will then repel the electromagnets and rotate the shaft as an electric motor. If the current is DC, the split-ring commutators are required to create a DC motor. If the current is AC, the two slip rings are required to create an AC motor. Examine an unplugged electric motor to see how both a motor and generator looks inside.

Summary Moving wire through a magnetic field generates electrical current. Electrical generators rotate a coil of wires through a magnetic field. The difference between an AC and a DC generator is that the AC generator uses slip rings to transfer the current to the electrical circuit, while the DC generator uses a split-ring commutator. Very large generators create electricity for the community. An electric motor is very similar to a generator, except that power is provided to turn the rotors.

Electromagnetic Devices by Ron Kurtus (revised 31 March 2009) Electromagnets are used in a number of everyday devices. One useful characteristic of an electromagnet is the fact that you can vary its magnetic force by changing the amount and direction of the current going through the coils or windings around it. Loudspeakers and tape recorders are devices that apply this effect. Some electromagnets can be very strong and its power can be readily turned off and on. Junk yard electromagnets, common doorbells and electromagnetic locks are examples. Electromagnets can also be used to create continual motion when opposed by other electromagnets or permanent magnets. Examples include electric motors and maglev trains. Questions you may have include: •

What devices use variations of electromagnetic force?

•

How can turning the magnetic field on and off be used?

•

What devices create conintual motion?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator.

Devices using varying field You can change the strength of an electromagnet's magnetic field by varying the electrical current that passes through the wires wrapped around it. If you change the direction of the electrical current the polarity of the magnetic field reverses. These effects can be used to move a loudspeaker cone back and forth, creating sound according to the electrical current through the wire. They also can be used to create magnetic fields in a magnetic tape or computer hard drive, such that it stores information.

Loudspeaker The loudspeakers in your radio, television or stereo system consists of a permanent magnet surrounding an electromagnet that is attached to the loudspeaker membrane or cone. By varying the electric current through the wires around the electromagnet, the electromanget and the speaker cone can be made to back and forth. If the variation of the electric current is at the same frequencies of sound waves, the resulting vibration of the speaker cone will create sound waves, including that from voice and music.

Cutout of a loudspeaker

If you examine the back area of a loudspeaker, you should be able to see the permanent magnet and coil of wire for the electromagnet. Some loudspeakers use an electromagnet without the iron core, which is called a solenoid.

Tape recorder When a mylar tape covered with fine iron dust passes near a small electromagnet that has a varying mangtic field, according to an electrical signal, the dust become magnetized in different directions. The electrical signal could be from a radio or microphone. The tape then is a record of the electrical signal. When it passes by another small electromagnet, it creates an electrical signal, duplicating that of the original signal. This signal can be amplified and played back through loudspeakers.

Devices using turning magnetic field on and off The magnetic strength of an electromagnet depends on the number of turns of wire around the electromagnet's core, the current through the wire and the size of the iron core. Increasing these factors can result in an electromagnet that is much larger and stronger than a natural magnet. For example, there is no known natrual magnet that is able to pick up a large steel object such as a car, but industrial electromagnets are capable of such a task. Also, if the core of the electromagnet is made of soft iron, its magnetic force can be turned off by turning off the electricity to the electromagnet.

Picking up and dropped junk cars Thus, an electromagnet can be used to pick up a piece of iron and then drop it someplace else.

Crane uses electromagnet to pick up junked car

Strong electromagnets are often used in areas of heavy industry to move large pieces of iron or steel. They are commonly employed in junkyards, where a crane with a huge electromagnet is used to pick up, move and drop old, junked cars.

Electromagnetic lock An electromagnetic lock be used to lock a door by creating a strong field in an electromagnet that is in contact with a magnetic plate. As long as there is current through the electromagnet, the door remains closed and locked. Another type of electromagnetic lock uses an electromagnet to extend a plunger between the doors, making it nearly impossible to open the door until the electromagnet releases the plunger.

Doorbell ringer An old-fashioned doorbell used an electromagnet that was rapidly turned on and off to pull a clanger against a bell.

Devises creating steady motion Clever use of electromagnetic forces can create steady motion.

Electric motor

An electric motor is another application of electromagnets. Suppose you put some electromagnets on a wheel and put some permanent magnets around the wheel. The electromagnets could be made to attract and repel the surrounding magnets, causing the wheel to turn. By varying the current, the speed of the motor can be made to vary. Look at an electric motor and see the internal wheel made of electromagnets and the outer shell made of permanent magnetic material.

Maglev trains A maglev (magnetic levitation) train works without wheels and is propelled by electromagnetic forces. This type of train usually consists of a set of magnets along the bottom of the train and a series of electromagnets on the tracks or guideway for the train. The electromagnets are adjusted to have the same polarity as the train's magnets, though complex computer controls. Since the magnetic poles repel, the train is levitated or floats slightly above the track. Guides on the sides prevent the train from sliding off. Depending on the position of the train, the polarity of the electromagnets is adjusted, causing the train to move forward. Maglev trains can reach speeds over 260 mile per hour or 430 kilometers per hour.

Summary Electromagnets are used in a number of devices, such as loudspeakers and tape recorders. Some electromagnets can be very strong and its power can be readily turned off and on, such as in junk yard electromagnets and electromagnetic locks. Electromagnets can also be used to create continual motion such as with electric motors and maglev trains.

Magnets by Ron Kurtus (revised 24 November 2004) A magnet is an object or material that attracts certain metals, such as iron, nickel and cobalt. It can also attract or repel another magnet. All magnets have North-seeking (N) and South-seeking (S) poles. When magnets are placed near each other, opposite poles attract and like poles repel each other. Various electrical devices make use of magnets. Questions you may have include: •

What types of magnets are there?

•

What are some common properties of magnets?

•

Where are magnets used?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator.

Types of magnets There are permanent magnets, temporary magnets and electromagnets.

Permanent magnets A permanent magnet is one that will hold its magnetic properties over a long period of time. Magnetite

Magnetite is a magnetic material found in nature. It is a permanent magnet, but it is relatively weak. Alloys Most permanent magnets we use are manufactured and are a combination or alloy of iron, nickel and cobalt. Rare-earth permanent magnets are a special type of magnet that can have extreme strength.

Temporary magnets A temporary magnet is one that will lose its magnetism. For example, soft iron can be made into a temporary magnet, but it will lose its magnetic power in a short while.

Electromagnet By wrapping a wire around an iron or steel core and running an electrical current through the wire, you can magnetize the metal and make an electromagnet. If the core is soft iron, the magnetism will diminish as soon as the current is turned off. This feature makes electromagnets good for picking up and dropping objects. Typically DC electricity is used, but AC current will also result in an electromagnet. (See Electromagnetism for more information.)

Properties of magnets Magnets always have two poles, come in various shapes, and attract or repel other magnets.

Names of poles All magnets have a North-seeking pole (N) and South-seeking pole (S). In a compass, the side marked (N) will point toward the Earth's North magnetic pole. Thus, it is called the "North-seeking pole." Also note that the Earth's North magnetic pole is not the same thing as the North Pole. They are actually several hundred miles apart. NOTE: To avoid confusion, you should try to be exact in what you are describing, especially concerning magnets.

Various shapes The magnet can be made into various shapes. The bar magnet is the most common configuration.

Bar magnet

Magnets also can be square, spherical, shaped like a horseshoe, and even shaped like a donut.

Horseshoe magnet

If you put an iron plate across the N and S poles of a horseshoe magnet, that would essentially "short circuit" the effect of the magnetism, such that its strength would not be very great. As soon as the plate was removed, the magnet would regain its full strength. That method is sometimes used in magnets that are temporary to help keep their magnetic properties for a longer time.

Cutting a magnet An interesting characteristic of magnets is that when you cut a magnet into parts, each part will have both N and S poles.

Bar magnet cut into three parts

Attraction and repulsion Magnets strongly attract iron, nickel and cobalt, as well as combinations or alloys of these metals. Also, unlike poles of two magnets will attract, but like poles will repel. Thus, N and S attract, while S and S will repel each other.

Applications There are numerous applications of magnets.

Creating a magnet You can magnetize a piece of steel by rubbing a magnet in one direction along the steel. This lines up the many of the domains or sections of aligned atoms in the steel, such that it acts like a magnet. The steel often won't remain magnetized for a very long time, while the true magnet is "permanently" magnetized and retains its strength for a long time. If you use soft iron or steel, such as a paper clip, it will lose its magnetism quickly. Also, you can disorient the atoms in a magnetized needle by heating it or by dropping the needle on a hard object.

Compass The first true application of a magnet was the compass, which not only helps in navigation by pointing toward the North magnetic pole, but it is also useful in detecting small magnetic fields. A compass is simply a thin magnet or magnetized iron needle balanced on a pivot. The needle will rotate to point toward the opposite pole of a magnet. It can be very sensitive to small magnetic fields.

Other uses Magnets are found in loudspeakers, electrical motors and electrical generators. A very common application of magnets is to stick things to the refrigerator. Since the outer shell of most refrigerators is made of steel, a magnet will readily stick to it. The type of magnets used often consists of a thin sheet of a magnetic material. As a novelty, magnetic disks can be stacked on a pencil to show magnetic levitation.

Levitating magnets

Summary A magnet attracts iron, nickel, cobalt and combinations of those metals. All magnets have North-seeking (N) and South-seeking (S) poles. When magnets are placed near each other, opposite poles attract and similar poles repel each other. Magnets are found in many of our electrical appliances.

Direct Current (DC) Electricity by Ron Kurtus (revised 11 January 2004) Direct current or DC electricity is the continuous movement of electrons from an area of negative (−) charges to an area of positive (+) charges through a conducting material such as a metal wire. Whereas static electricity sparks consist of the sudden movement of

electrons from a negative to positive surface, DC electricity is the continuous movement of the electrons through a wire. A DC circuit is necessary to allow the current or steam of electrons to flow. Such a circuit consists of a source of electrical energy (such as a battery) and a conducting wire running from the positive end of the source to the negative terminal. Electrical devices may be included in the circuit. DC electricity in a circuit consists of voltage, current and resistance. The flow of DC electricity is similar to the flow of water through a hose. Questions you may have include: •

What is DC electricity?

•

What are voltage, current and resistance?

•

How do we create DC electricity?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator. Note: Click the Play button to hear the text being read.

Time = 6 min. 47 sec.

Continuous movement of electrons DC electricity is the continuous movement of electrons through a conducting material such as a metal wire. The electrons move toward a positive (+) potential in the wire.

DC movement of electrons in wire

In reality, there are millions of electrons weaving their way among the atoms in the wire. This is just an illustration of the movement.

Electrical circuit An electrical circuit consisting of a source of DC power and a wire making a complete circuit is required for DC electricity to flow. (See DC circuits for more information.)

A flashlight is a good example of a DC circuit

Current shown opposite

Although the negative charged electrons move through the wire toward the positive (+) terminal of the source of electricity, the current is indicated as going from positive to negative. This is an unfortunate and confusing convention. Ben Franklin originally named charges positive (+) and negative (−) when he was studying static electricity. Later, when scientists were experimenting with electrical currents, they said that electricity travels from (+) to (−), and that became the convention. This was before electrons were discovered. In reality, the negative charged electrons move toward the positive, which is the opposite direction that people show current moving. It is confusing, but once a convention is made, it is difficult to correct it.

Voltage, current and resistance The electricity moving through a wire or other conductor consists of its voltage (V), current (I) and resistance (R). Voltage is potential energy, current is the amount of electrons flowing through the wire, and resistance is the friction force on the electron flow. A good way to picture DC electricity and to understand the relationship between voltage, current and resistance is to think of the flow of water through a hose, as explained below.

Electrical voltage A potential or pressure builds up at one end of the wire, due to an excess of negatively charged electrons. It is like water pressure building up in a hose. The pressure causes the electrons to move through the wire to the area of positive charge. This potential energy is called Voltage, its unit of measurement is the Volt.

Electrical current The number of electrons is called current and its unit of measurement is the Ampere or Amp. Electrical current is like the rate that water flows through a hose.

Resistance An Ohm is the unit of measurement of the electrical resistance. A conductor like a piece of metal has its atoms so arranged that electrons can readily pass around the atoms with little friction or resistance. In a nonconductor or poor conductor, the atoms are so arranged as to greatly resist or impede the travel of the electrons. This resistance is similar to the friction of the hose against the water moving through it.

Comparison with hose The following chart compares water running in a hose and DC electricity flowing in a wire: Water in a Hose

DC in a Wire

Electrical Units

pressure

potential (V)

Volts

rate of flow

current (I)

Amps

friction

resistance (R)

Ohms

Analogy between a Hose and Electricity in a Wire

Creating DC electricity

Although static electricity can be discharged through a metal wire, it is not a continuous source of DC electricity. Instead, batteries and DC generators are used to create DC.

Batteries Batteries rely on chemical reactions to create DC electricity. Car battery The automobile battery consists of lead plates in a sulfuric acid solution. When the plates are given a charge from the car's generator or alternator, they change chemically and hold the charge. That source of DC electricity can then be used to power the car's lights and such. The biggest problem with this type of battery is that sulfuric acid is very caustic and dangerous. Lemon battery Another battery that you can make yourself is a lemon battery. This one needs no charging but depends on the acidic reaction of different metals. Copper and zinc work the best. You can use a copper penny or copper piece of wire. A zinccoated or galvanized nail can be used as the other terminal. A standard iron nail will work, but not as good. Push the copper wire and galvanized nail into an ordinary lemon and measure the voltage across the metals with a voltmeter. Some people have been able to dimly light a flashlight bulb with this battery.

DC generator Another reliable source of DC electricity is the DC generator, which consists of coils of wire spinning between North and South magnets. (See Generating Electrical Current for more information.)

Summary Direct current or DC electricity is the continuous movement of electrons from negative to positive through a conducting material such as a metal wire. A DC circuit is necessary to allow the current or steam of electrons to flow. In a circuit, the direction of the current is opposite the flow of electrons. DC electricity in a circuit consists of voltage, current and resistance. The flow of DC electricity is similar to the flow of water through a hose. Batteries and DC generators are the sources to create DC electricity.

Alternating Current (AC) Electricity by Ron Kurtus (revised 5 December 2008) Alternating current (AC) electricity is the type of electricity commonly used in homes and businesses throughout the world. AC is different than the direct current (DC) electricity that comes from a battery and flows in one direction through the wire. AC electricity alternates directions. The back-and-forth motion occurs between 50 and 60 times per second, depending on the electrical system of the country. AC electricity is created by an AC electric generator, which determines the frequency. What is special about AC electricity is that the voltage can be readily changed, thus making it more suitable for long-distance transmission than DC electricity. But also, AC can employ capacitors and inductors in electronic circuitry, allowing for a wide range of applications. Note: We say AC electricity instead of simply saying AC, since that is also the abbreviation for air conditioning. You need to be exact in science to avoid any misunderstandings.

Questions you may have include:

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What is the difference between AC and DC electricity?

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Why do we use AC instead of DC?

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How do we create AC electricity?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator.

Movement of electrons in AC Electrons have negative (−) electrical charges. Since opposite charges attract, they will move toward an area consisting of positive (+) charges. This movement is made easier in an electrical conductor, such as a metal wire.

Electrons move direct with DC electricity With DC electricity, connecting a wire from the negative (−) terminal of a battery to the positive (+) terminal will cause the negative charged electrons to rush through the wire toward the positive charged side. The same thing happens with a DC generator, where the motion of coiled wire through a magnetic field pushes electrons out of one terminal and attracts electrons to the other terminal.

Electrons alternate directions in AC electricity With an AC generator, a slightly different configuration alternates the push and pull of each generator terminal. Thus the electricity in the wire moves in one direction for a short while and then reverses its direction when the generator armature is in a different position. This illustration gives an idea of how the electrons move through a wire in AC electricity. Of course, both ends of the wire extend to the AC generator or source of power.

AC movement of electrons in wire

The charge at the ends of the wire alternates between negative (−) and positive (+). If the charge is negative (−), that pushes the negatively charged electrons away from that terminal. If the charge is positive (+), the electrons are attracted in that direction. Rate of change AC electricity alternates back-and-forth in direction 50 or 60 times per second, according to the electrical system in the country. This is called the frequency and is designated as either 50 Hertz (50Hz) or 60 Hertz (60Hz). (See Worldwide AC Voltages and Frequencies for more information.)

Light bulbs Many electrical devices—like light bulbs—only require that the electrons move. They don't care if the electrons flow through the wire or simply move back-and-forth. Thus a light bulb can be used with either AC or DC electricity.

AC is periodic motion The regular back-and-forth motion of the electrons in a wire when powered by AC electricity is periodic motion, similar to that of a pendulum.

(See Periodic Motion and Pendulum for more information.) Because of this periodic motion of the electrons, the voltage and current follow a sine waveform, alternating between positive (+) and negative (−), as measured with a voltmeter or multimeter.

Waveform varies between positive and negative as it travels in time

The rate that the voltage or current peaks pass a given point is the frequency of the AC electricity.

Transformer The major advantage that AC electricity has over DC electricity is that AC voltages can be transformed to higher or lower voltage levels, while it is difficult to do that with DC voltages. When DC electricity was used supplied to homes is usually High voltages are necessary for sending electricity great distances. This means that the high voltages used to send electricity over great distances from the power station could be reduced to a safer voltage for use in the house. Changing voltages is done by the use of a transformer. This device uses properties of AC electromagnets to change the voltages. (See AC Transformers for more information.)

Tuning circuits AC electricity also allows for the use of a capacitor and inductor within an electrical or electronic circuit. These devices can affect the way the alternating current passes through a circuit. They are only effective with AC electricity. A combination of a capacitor, inductor and resistor is used as a tuner in radios and televisions. Without those devices, tuning to different stations would be very difficult.

Summary We commonly use AC electricity to power our television, lights and computers. In AC electricity, the current alternates in direction. AC electricity was proven to be better for supplying electricity than DC, primarily because the voltages can be transformed. AC also allows for other devices to be used, opening a wide range of applications.

Alternating Current (AC) Transformers by Ron Kurtus (revised 8 February 2009)

A transformer is an electrical device that is used to change the voltage in alternating current (AC) electrical circuits. The fact that the potential energy can be readily changed from one voltage to another through the use of a transformer is a major advantage of AC electricity over direct current (DC). AC transformers can change power line high voltages to house current voltage. They also are used to change the voltage from house current to that used by low voltage devices. Often the AC in these small transformers or adapters is also changed to DC. Questions you may have include: •

How does the transformer work?

•

What are the principles of electricity and magnetism involved?

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What are some uses of transformers?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator.

Basic principles of transformers A transformer combines several major characteristics of electricity and magnetism to change AC voltages. First of all, you need to know the principles for creating an electromagnet and creating electricity.

Creating an electromagnet A wire with DC electric current flowing through it has a magnetic field around it. Placing a compass near a wire and observing the needle move when the DC current is turned on can demonstrate this. By wrapping the wire around a piece of iron, the magnetic field is increased many times due to the realignment of the iron atoms, each which acts as a tiny magnet. The iron core and wire wrapping is called an electromagnet. Relation to voltage The greater the current through the wire the greater the strength of the electromagnetic field. Since voltage and current are proportional for a given resistance, according to Ohm's Law V = IR, the strength of the electromagnetic field is proportional to the voltage used. Double the voltage and you double the strength of the electromagnet. (See Ohm's Law for Electrical Circuits for more information.) Relation to turns of wire The greater the number of turns around the iron core the greater the strength of the electromagnet. The strength is approximately proportional to the number of turns. Triple the number of turns and you triple the strength of the electromagnet. (Experiment idea: measure the change of strength of an electromagnet by changing the voltage and/or number of turns.) Direction of magnetism The direction of the magnetic field is determined by the direction of the current and the direction of the turns around the iron core. If you change the direction of the current, the north and south poles of the electromagnet will switch. With DC electricity, you must physically change the wires to change the direction of the current. With AC electricity, the direction changes with each cycle.

Thus, one end of an AC electromagnet is switching from north to south and back again 60 times per second in the U.S. or 50 times per second in some other countries.

Creating electricity Electricity is created either when a wire is moved through a magnetic field or when a magnetic field is moved past a wire. Moving the magnetic field past the wire can be done by physically moving a magnet past the wire or by somehow changing the amount of the magnetic field.

Transforming the voltage To transform or change the voltage of AC electricity, you use an AC electromagnet and the principles described above.

AC electromagnet An AC electromagnet continually changes the direction of its magnetic field. This means the field goes from zero to N to zero to S and so on. If you would put an AC electromagnet near a wire, then the changing magnetic field should create a current in the wire. Or better yet, why not wrap the wire around the iron core of the electromagnet? This is how a transformer works.

Transformer A transformer can be a long piece of iron with wire having with AC current going through it and wrapped around the piece of iron near one end. It also has wire that creates electrical current wrapped around it at the other end. A more common configuration is a square or donut shaped iron core with the wire wrapping on both sides.

Transformer changes voltage

Output proportional to turns The strength of the magnetic field is proportion to the input voltage and the number of turns around the core (called the primary coil). By reversing the rule, the output voltage is proportional to the strength of the changing magnetic field and the number of turns (called the secondary coil). For example, if you wanted to increase your house voltage from 110 volts (110V) to 220V in order to power your electric stove, you could use a transformer with twice the turns in the secondary coil as in the primary coil. The relationship is written as:

input volts / input turns = output volts / output turns 110V / 5 turns = 22 = 220V / 10 turns

Using transformers Transformers are used to lower voltage to be safer to use in your house. You may also use an adapter to lower the voltage even more for some devices you use. DC transformers are now available, but they won't replace AC transformers.

House voltage Normally, the current in the electrical lines outside your house are around 1100V AC. The reason it is so high is that the electricity travels more effectively over long distances at higher voltages. High voltage lines carry up to 10,000 volts. The transformer near to top of the electrical pole changes the voltage to a safer 110V for your house.

Adapters Most people use adapters when they power devices that also use batteries. An adapter is a transformer that changes the 110V AC house current to 12V DC or 9V DC that is used by the device. It also changes the AC to DC, because the device works on batteries. Changing AC to DC is done by electronic circuitry called a rectifier. It essentially chops off 1/2 of the AC current to make it similar to DC. Some of the lost AC current is turned into heat. That is one reason your adapters sometimes get warm.

DC transformers You can see that DC voltages could not be changed with the configuration of the transformer. This is because the DC current would not be changing the magnetic field the way AC current does. And this was the reason that AC won over DC when electricity started to be used around the world. Since then, electrical engineers have developed DC transformers, primarily using special circuitry. Since most everyone now uses AC, it is too late to change the system.

Summary The principles for creating an AC electromagnet and changing magnetic fields lead to how a transformer works. The output voltage of a transformer is proportional to the ratio of the number of turns of the coils. Transformers reduce the high voltage to a safer home voltage, as well as to reduce 110V AC to what can be used in some battery-powered devices.

Worldwide AC Voltages and Frequencies by Ron Kurtus (revised 18 August 2005) The voltage and frequency of alternating current (AC) electricity used in homes varies from country to country throughout the world. Typically either 110-volt AC (110V) or 220-volt AC (220V) are used. Note that 110 volts and 220 volts are averages, since the voltage does fluctuate during usage. Most countries use 50Hz (50 Hertz or 50 cycles per second) as the frequency of their AC. Only a handful use 60Hz. The United States uses 110V and 60Hz AC electricity. Questions you may have include:

•

How were the voltage and frequency values selected?

•

What happens when you visit another country?

•

What is the listing for the various countries?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator. Note: Click the Play button to hear the text being read.

Time = 8 min. 6 sec.

How values were selected The type of electricity delivered to homes and businesses was first direct current (DC) but then changed to AC electricity. The standard voltage level started at 110V, went to 240V, back to 110V, and then to 220V. The frequency started at 60Hz and then went to 50Hz in most areas.

Tesla starts AC Early in the history or electricity, Thomas Edison's General Electric Company was distributing DC electricity at 110 volts in the United States. Then Nikola Tesla devised a system of three-phase AC electricity at 240 volts. Three-phase meant that three alternating currents slightly out of phase were combined in order to even out the great variations in voltage occurring in AC electricity. He had calculated that 60 cycles per second or 60Hz was the most effective frequency. Tesla later compromised to reduce the voltage to 110 volts for safety reasons.

Europe goes to 50Hz With the backing of the Westinghouse Company, Tesla's AC system became the standard in the United States. Meanwhile, the German company AEG started generating electricity and became a virtual monopoly in Europe. They decided to use 50Hz instead of 60Hz to better fit their metric standards, but they kept the voltage at 110V. Unfortunately, 50Hz AC has greater losses and is not as efficient as 60HZ. Due to the slower speed 50Hz electrical generators are 20% less effective than 60Hz generators. Electrical transmission at 50Hz is about 10-15% less efficient. 50Hz transformers require larger windings and 50Hz electric motors are less efficient than those meant to run at 60Hz. They are more costly to make to handle the electrical losses and the extra heat generated at the lower frequency.

Europe goes to 220V Europe stayed at 110V AC until the 1950s, just after World War II. They then switched over to 220V for better efficiency in electrical transmission. Great Britain not only switched to 220V, but they also changed from 60Hz to 50Hz to follow the European lead. Since many people did not yet have electrical appliances in Europe after the war, the change-over was not that expensive for them.

U.S. stays at 110V, 60Hz The United States also considered converting to 220V for home use but felt it would be too costly, due to all the 110V electrical appliances people had. A compromise was made in the U.S. in that 220V would come into the house where it would be split to 110V to power most

appliances. Certain household appliances such as the electric stove and electric clothes dryer would be powered at 220V.

When visiting another country Bringing an electrical appliance from one country to another may require some special converters, transformers and adapters to allow the appliance or device to work properly.

Converters Converters are typically used to decrease the AC voltage from 220V to the 110V level needed by the appliance. They are only used for simple electrical products such as hair dryers, steam irons, shavers, or small fans. They are only used for short periods of time, can only be used for ungrounded appliances, and must be unplugged from the wall when not in use. Converters cannot be used by electronic devices such as radios or computers. A transformer is used for those devices. The reason is that a converter simply cuts the AC sine wave in half, reducing the voltage. Electronic devices need the full sine wave to function properly. Some converters will also change AC to DC. An example is converting 120V AC to 12V DC.

Transformers Transformers are used to increase or decrease the voltage and should be used with electronic devices such as radios, televisions, computers and other devices having electronics circuitry. Transformers are more expensive than converters. They can also be used with electric appliances and may be operated continually for many days. A device like a hair dryer does not have any electronic circuitry. It simply has a heatingr element and electric fan, so it can use either a converter or transformer.

Dual voltage devices Some devices have a built-in converter or transformer, such that they are called dual voltage devices. Most laptop battery chargers and AC adapters are dual voltage, so they can be used with only a plug adapter for the country you are visiting.

Plug Adapters Outlet plugs are different in the various countries. Plug adapter must often be used when visiting a different country. These adapters do not convert electricity. Rather, they simply allow a dual voltage appliance, transformer or converter from one country to be plugged into the wall outlet of another country.

Frequency difference Converters and transformers only change the voltage and not the frequency. The result is that a motor in a 50Hz appliance will operate slightly faster on 60Hz electricity. Likewise, a clock made for 60Hz will run slower in a country using the 50Hz frequency. Most modern electronic equipment like computers, printers, DVD players and stereos are usually not affected by the frequency difference.

Country listing Of the over 200 countries listed below, less than 40 use 110V. Some countries use dual voltages. 43 countries use 60Hz, while the rest use 50Hz.

Country Voltage Frequency Afghanistan 220V 50Hz Albania 230V 50Hz Algeria 230V 50Hz American Samoa 120V 60Hz Andorra 230V 50Hz Angola 220V 50Hz Anguilla 110V 60Hz Antigua 230V 60Hz Argentina 220V 50Hz Armenia 230V 50Hz Aruba 127V 60Hz Australia 240V 50Hz Austria 230V 50Hz Azerbaijan 220V 50Hz Azores 230V 50Hz Bahamas 120V 60Hz Bahrain 230V 50Hz Balearic Islands 230V 50Hz Bangladesh 220V 50Hz Barbados 115V 50Hz Belarus 230V 50Hz Belgium 230V 50Hz Belize 110/220V 60Hz Benin 220V 50Hz Bermuda 120V 60Hz Bhutan 230V 50Hz Bolivia 230V 50Hz Bosnia 230V 50Hz Botswana 230V 50Hz Brazil 110-220V 60Hz Brunei 240V 50Hz Bulgaria 230V 50Hz Burkina Faso 220V 50Hz Burundi 220V 50Hz Cambodia 230V 50Hz Cameroon 220V 50Hz Canada 120V 60Hz Canary Islands 230V 50Hz Cape Verde 230V 50Hz Cayman Islands 120V 60Hz Central Africa 220V 50Hz Chad 220V 50Hz Channel Islands 230V 50Hz Chile 220V 50Hz China 220V 50Hz Colombia 110V 60Hz

Country Kiribati Korea, South Kuwait Kyrgyzstan Laos Latvia Lebanon Lesotho Liberia Libya Lithuania Liechtenstein Luxembourg Macau Macedonia Madagascar Madeira Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mexico Micronesia Moldova Monaco Mongolia Montserrat Islands Morocco Mozambique Myanmar (Burma) Namibia Nauru Nepal Netherlands Netherlands Antilles New Caledonia New Zealand Nicaragua Niger Nigeria Norway Okinawa

Voltage Frequency. 240V 50Hz 220V 60Hz 240V 50Hz 220V 50Hz 230V 50Hz 230V 50Hz 230V 50Hz 220V 50Hz 120V 60Hz 127/230V 50Hz 230V 50Hz 230V 50Hz 230V 50Hz 220V 50Hz 230V 50Hz 127/220V 50Hz 230V 50Hz 230V 50Hz 240V 50Hz 230V 50Hz 220V 50Hz 230V 50Hz 220V 50Hz 220V 50Hz 230V 50Hz 127V 60Hz 120V 60Hz 230V 50Hz 230V 50Hz 230V 50Hz 230V 60Hz 220V 50Hz 220V 50Hz 230V 50Hz 220V 50Hz 240V 50Hz 230V 50Hz 230V 50Hz 127/220V 50Hz 220V 50Hz 230V 50Hz 120V 60Hz 220V 50Hz 240V 50Hz 230V 50Hz 100V 60Hz

Comoros 220V Congo (Zaire) 220V Cook Islands 240V Costa Rica 120V Côte d'Ivoire 220V (Ivory Coast) Croatia 230V Cuba 110/220V Cyprus 230V Czech Republic 230V Denmark 230V Djibouti 220V Dominica 230V Dominican 110V Republic East Timor 220V Ecuador 127V Egypt 220V El Salvador 115V Equatorial Guinea 220V Eritrea 230V Estonia 230V Ethiopia 220V Faeroe Islands 230V Falkland Islands 240V Fiji 240V Finland 230V France 230V French Guyana 220V Gaza 230V Gabon 220V Gambia 230V Germany 230V Ghana 230V Gibraltar 230V Greece 230V Greenland 230V Grenada 230V Guadeloupe 230V Guam 110V Guatemala 120V Guinea 220V Guinea-Bissau 220V Guyana 240V Haiti 110V Honduras 110V Hong Kong 220V

50Hz 50Hz 50Hz 60Hz 50Hz 50Hz 60Hz 50Hz 50Hz 50Hz 50Hz 50Hz 60Hz 50Hz 60Hz 50Hz 60Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 60Hz 60Hz 50Hz 50Hz 60Hz 60Hz 60Hz 50Hz

Oman 240V Pakistan 230V Palmyra Atoll 120V Panama 110V Papua New Guinea 240V Paraguay 220V Peru 220V Philippines 220V Poland 230V Portugal 230V Puerto Rico 120V Qatar 240V Réunion Island 230V Romania 230V Russian Federation 230V Rwanda 230V St. Kitts & Nevis 230V Islands St. Lucia Island 240V St. Vincent Island 230V Saudi Arabia 127/220V Senegal 230V Serbia & Montenegro 230V Seychelles 240V Sierra Leone 230V Singapore 230V Slovakia 230V Slovenia 230V Somalia 220V South Africa 230V Spain 230V Sri Lanka 230V Sudan 230V Suriname 127V Swaziland 230V Sweden 230V Switzerland 230V Syria 220V Tahiti 110/220V Tajikistan 220V Taiwan 110V Tanzania 230V Thailand 220V Togo 220V Tonga 240V Trinidad & Tobago 115V Tunisia 230V

50Hz 50Hz 60Hz 60Hz 50Hz 50Hz 60Hz 60Hz 50Hz 50Hz 60Hz 50Hz 50Hz 50Hz 50Hz 50Hz 60Hz 50Hz 50Hz 60Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 60Hz 50Hz 50Hz 50Hz 50Hz 60Hz 50Hz 60Hz 50Hz 50Hz 50Hz 50Hz 60Hz 50Hz

Hungary Iceland India Indonesia Iran Iraq Ireland (Eire) Isle of Man Israel Italy Jamaica Japan Jordan Kenya Kazakhstan

230V 230V 240V 230V 230V 230V 230V 230V 230V 230V 110V 100V 230V 240V 220V

50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 50/60Hz 50Hz 50Hz 50Hz

Turkey 230V Turkmenistan 220V Uganda 240V Ukraine 230V United Arab Emirates 220V United Kingdom 230V United States 110/220V Uruguay 220V Uzbekistan 220V Venezuela 120V Vietnam 220V Virgin Islands 110V Western Samoa 230V Yemen 230V Zambia 230V Zimbabwe 220V

50Hz 50Hz 50Hz 50Hz 50Hz 50Hz 60Hz 50Hz 50Hz 60Hz 50Hz 60Hz 50Hz 50Hz 50Hz 50Hz

Exceptions Some countries can't decide on a standard. Brazil In Brazil, most states use between 110V and 127V AC electricity. But many hotels use 220V. In the capital Brasilia and in the northeast of the country, they mainly use 220-240V. Japan In Japan, they use the same voltage everywhere, but the frequency differs from region to region. Eastern Japan, which includes Tokyo, uses 50Hz. In western Japan, which includes Osaka and Kyoto, they use 60 Hz. The reason for this is that after World War II, Britain was in charge of helping reconstruct Japan's electrical system in the eastern part of the country and the United States set up the electricity in the western part of Japan. Since Great Britain (United Kingdom) had been using 60Hz before the war and had just switched over to the European 240V 50Hz, it is strange that they set up Japan at 100V and 50Hz, especially when the U.S. was using 60Hz. Having different voltages and frequencies within the country not only must be confusing for the people but also can result in extra costs for appliances and adapters.

Summary The voltage and frequency of AC electricity varies from country to country throughout the world. Most use 220V and 50Hz. About 20% of the countries use 110V and/or 60Hz to power their homes. 220V and 60Hz are the most efficient values, but only a few countries use that combination. The United States uses 110V and 60Hz AC electricity.

Electrical Power by Ron Kurtus (revised 14 August 2005) The electrical power used in operate an electrical device is defined as the potential energy or voltage times the current passing through the device. This could also apply to a whole electrical system, such as the the power used in running your household appliances. This is compared to the mechanical definition of power as the work done over a period of time. The

electric company uses the power used over a period of time to calculate the energy used and thus your electric bill. It is compared with the power required to do some work over a period of time. Questions you may have include: •

How do you determine electrical power?

•

How do we measure electrical power?

•

How is your electric bill calculated?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion | Scientific Calculator. Note: Click the Play button to hear the text being read.

Time = 4 min. 38 sec.

Determining electric power The electrical power required to operate a device is the input voltage times the current required. P = VI where

•

P = electrical power

•

V = voltage used

•

I = current in amperes

•

VI is V times I

Electrical power is measured in watts. If the amount of watts is large, kilowatts are used. 1 kilowatt = 1000 watts, just as 1 kilometer = 1000 meters. The abbreviation for kilowatt is usually kW.

Current If you look at the top of a light bulb, you will see its power rating. One example is a 100 watt light bulb. Thus P = 100W. You can use the equation P = VI for electrical power to determine the amount of current passing through that light bulb. If your house voltage is V = 110 volts, then you can see that 100W = 110V * I. Thus I = 100 / 110 = 0.91 amps.

Resistance You can also find the resistance of the light bulb, using Ohm's Law: V = IR. V = 110V I = 0.91A V = IR = 110V = 0.91A * R Thus R = 110 / 0.91 = 120.9 ohms.

Comparing with mechanical power

The standard or mechanical definition of power is the work per unit time. (See Work for more on that subject.) In other words, power equals work divided by time. P=W/T where P = power in watts, W = the work done in joules and T = the time of measurement. Since energy is often defined as the ability to do work, let's substitute energy E for work and rearrange the equation: E = PT Thus, the electrical energy used is the electrical power times the time. If we measure the electrical power as kilowatts and the time as hours, we get the energy used by an electrical system in terms of kilowatt-hours. That is the unit of measurement the electric company uses when determining your bill.

Calculating your electric bill Knowing about electrical power can help you in understanding how your electric bill is calculated. The electric company sends you a bill determined by the amount of work the electricity has done or amount of energy expended in kilowatt-hours. Most homes have an electric meter outside that measures the amount of electrical energy used by the house over a period of time. Many electric companies charges about $0.07 per kilowatt-hour. Thus, you multiply the number of kilowatts of electricity you use times the amount of time you use it and multiply that by $0.07 to get your electric bill. For example, if you used a 1500-watt hair dryer for 100 hours in a month at a cost of $0.07 per kilowatt-hour, the electric company would bill you for: 1500 watt * 100 hours = 150,000 watt-hours = 150 kilowatt-hours. Thus your bill would amount to: 150 kilowatt-hours * $0.07 / kW-hr = $10.50.

Summary Electric power is voltage times current. Your electric bill is based on the electric power times the time used, in kilowatt-hours. Knowing how much power you used and the electric rate charged, you can determine your electric bill.