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6. Fundamentals of Magnetism CPD/WEB update February 22, 2009
Objectives 1.
To investigate the magnetic field created by a current carrying conductor.
2.
To investigate the force between a current carrying conductor and a static magnetic field.
3.
To investigate the voltage induced across a conductor as the conductor moves through a static magnetic field (or vice versa) and relate the observations to Faraday’s Law and Lenz’s Law.
Equipment 1. 2.
5V, 12V power supply, 4 multimeters,
3.
Compass,
4. 5. 6. 7. 8. 9. 10. 11.
Galvanometer, Inner and outer coil, Bar magnet, 1 Steel rod, Two or three 2 Ω power resistor, 25W, 10 Ω power resistor, 25W, Coil mounted on balance, 100 Ω rheostat, 25W (a rheostat is a variable resistor),
Preparation and Background Technical information and background on Experiment 6 is available in Chapters 33 and 34 of Knight. Before coming to the lab you should read the material in chapters 33 and 34 at least, then answer any questions and perform any calculations required in this preparation section. Write down any questions you have and ask them of a lab instructor during the lab period. If you do the pre-lab in advance of coming to the lab you will understand the lab better, find it easier to do, and be finished earlier.
EE1813 Lab Manual
Version 1.1
Page 53 of 102
Fundamentals of Magnetism 1.
Determine the direction of the force exerted on the conductor in Figure 6.1. Indicate the direction on the small copy of Figure 6.1 on the summary sheet.
2.
Determine the direction of forces exerted by the electromagnets in Figure 6.2 Indicate the direction on the small copy of Figure 6.2 on the summary sheet.
N
S
Figure 6.1 Force Exerted on Conductor
Figure 6.2 Force Exerted by Electromagnets
3.
A conductor moves with a constant velocity in a magnetic field in the direction shown in Figure 6.3. What is the polarity of the voltage measured at V. Indicate your answer on the small copy of Figure 6.3 on the summary sheet.
4.
What is the polarity of the voltage measured at V in Figure 6.4 when the switch, S, is suddenly closed at time t = 0? What happens to the voltage if the number of turns in the right side coil are doubled? Indicate your answer on the small copy of Figure 6.4 on the summary sheet.
+
S
V
–
N + S
V
–
Motion of Conductor
Figure 6.3 Voltage Induced on Conductor
Figure 6.4 Voltage Induced on the Secondary Coil
Experiment It is the Summary section beginning at page 58 that will be completed and submitted for evaluation. Only one report per group should be submitted. Be sure that all group members in attendance are noted at the top of the summary sheet. Important Safety Note : In this experiment you will use some power resistors and they will be carrying a large current. Be very careful not to touch these resistors as they get very hot and you Page 54 of 102
Version 1.1
EE1813 Lab Manual
Fundamentals of Magnetism could burn your fingers. For part 1 of the experiment, try to leave the power supply on for only short periods of time. The resistors may become hot enough to scorch the wood.
1. Magnet Field Produced by a Current Connect the 12 volt power supply through a long lead to two, 2-ohm power resistors in parallel. Hold the long lead away from the other leads and straight up and down. Hold the compass as close to the lead (which should be carrying about 10 amps of current), and observe the reaction of the compass needle as the compass is moved around the lead.
12V
compass 2Ω
2Ω
Figure 6.5 Probing a magnetic field around
Make two loops with the lead and place the a current carrying wire. compass in the centre of the loops. Place it above the loops, then below the loops, then beside the loops, observing the compass as you move it around the looped wires. Take a second long lead and insert it in the circuit and make a second pair of loops. Now put those loops together with the first two so the current direction is the same in both loops. Place the compass in the centre of the loops. Observe what happens. Turn one of the pairs of loops to face in the other direction. What happens then? Answer the questions in part 1 of the summary sheets.
2. Current from Motion of a Magnet Connect the galvanometer to the terminals of the outer coil. Insert the north pole of the bar magnet into the end of the coil opposite its terminals and note the polarity of the S N deflection of the galvanometer as shown in Figure 6.6 (if not marked, the North pole of + – G the magnet is painted red). Note : you will have to press and hold the galvanometer “onbutton” while making the measurement. Now Figure 6.6 Creating an Induced Voltage withdraw the north pole of the magnet and Using a Permanent Magnet in a Coil observe the effect. What is the effect of changing the speed of the bar magnet? What happens if the north pole of the magnet is inserted into the other end of the coil? Now hold the bar magnet stationary and move the coil over the bar magnet and observe the effect of changing direction and speed of the coil.
EE1813 Lab Manual
Version 1.1
Page 55 of 102
Fundamentals of Magnetism
3. Inductive Coupling of Coils
2Ω S
+
G
Connect the inner coil in series with the 2 Ω resistor, a single pole single throw (SPST) switch (this will be the switch on the power supply) and the 12V supply as shown in Figure 6.7. Carefully insert the inner coil into the outer coil. Connect a galvanometer across the terminals of the outer coil. Observe the effect of closing the switch, S, on the galvanometer reading. Now observe the effect of opening the switch on the galvanometer reading.
–
12V
Figure 6.7 Creating an Induced Voltage Using an Electromagnet in a Coil
4. Motion of Coil in Magnetic Field Connect the galvanometer to the coil mounted on the balance as shown in Figure 6.8, being sure to connect the coloured terminals correctly (red to red, black to black). The current direction in the coil and the orientation of the magnet pole faces has been indicated for you on the device. Do not, for any reason, remove or change the orientation of the magnet blocks in the horseshoe! Note that the exposed side of the coil is free to move between the poles of the horseshoe magnet. Note the deflection of the galvanometer as the coil is moved up through the magnetic field and down through the magnetic field. Verify your observations with the right hand generator rule.
G
Coil on Balance Magnet Figure 6.8 Coil on Balance with Galvanometer
5. Current-carrying Coil in Magnetic Field As indicated in Figure 6.9 on page 57, remove the galvanometer from the coil and connect the coil in a series circuit with the 5V supply, an ammeter, a 10 Ω resistor, and rheostat. Make certain that you connect the black terminal on the coil with the ground terminal on the power supply so that the current direction is correct. The rheostat may be used to adjust the current flow through the coil. Rotate the paddle so that the exposed side of the coil is directly between the poles of the magnet. Observe that a force is exerted on the coil when a current flows. What happens to the force as the current is increased and decreased? What happens if Page 56 of 102
Version 1.1
EE1813 Lab Manual
Fundamentals of Magnetism the polarity of the leads connected to the supply are reversed? Verify your observations with the left hand motor rule.
5V
10Ω
A
Coil on Balance Magnet
Figure 6.9 Coil on Balance with External Power Supply
EE1813 Lab Manual
Version 1.1
Page 57 of 102
Name(s):
ID(s):
Lab Group: Lab Day: Date:
6. SUMMARY SHEET: Fundamentals of Magnetism Answers to Preparation Questions: Mark the diagrams below in the same manner as you did in the preparation section. V
N
S
S
For Marker’s use only
34 For Marker’s use only
4
N
Motion of Conductor
Figure 5.3
Figure 5.1
V
S
Figure 5.4 Figure 5.2
For Marker’s use only
1. What happens as you move the compass around the lead carrying the current?
What happens as you place the compass in the coils of wire?
What happens when the compass is outside above the loop?
What happens when you place two pairs of loops together?
What happens when you reverse the two pairs of loops?
What do you notice about the relative strength of the earth’s magnetic field as compared to the field generated around the lead you are using?
Page 58 of 102
Version 1.1
EE1813 Lab Manual
6
Fundamentals of Magnetism 2. In Part 2 of the Experiment, what is the difference in effect on the galvanometer needle of moving the magnet out of the coil as compared to moving it in?
For Marker’s use only
6
What is the effect on the galvanometer needle of changing the speed of motion of the bar magnet?
What happens when the north pole of the bar magnet is inserted in the opposite end (the one with the terminals) of the coil? Why?
What happens when the coil moves relative to the stationary magnet? Why?
3. In Part 3 of the Experiment, describe the voltage measured with the galvanometer when the switch is pressed; describe the voltage measured when the switch is released. Explain the reason for the needle movements.
EE1813 Lab Manual
Version 1.1
Page 59 of 102
For Marker’s use only
6
Fundamentals of Magnetism 4. From Part 4 of the Experiment, carefully label the following diagram with magnet polarity, direction of conductor motion, galvanometer deflection and direction of current flow.
For Marker’s use only
8
G
Coil on Balance Magnet Figure 6.10 Coil on Balance with Galvanometer
5. From Part 5 of the Experiment, carefully label the following diagram with magnet polarity, direction of current flow and the direction of the force exerted on the conductor.
5V
10Ω
A
Coil on Balance Magnet Figure 6.11 Coil on Balance with External Power Supply
Page 60 of 102
Version 1.1
EE1813 Lab Manual
For Marker’s use only
4
Objectives 1.
To investigate the magnetic field created by a current carrying conductor.
2.
To investigate the force between a current carrying conductor and a static magnetic field.
3.
To investigate the voltage induced across a conductor as the conductor moves through a static magnetic field (or vice versa) and relate the observations to Faraday’s Law and Lenz’s Law.
Equipment 1. 2.
5V, 12V power supply, 4 multimeters,
3.
Compass,
4. 5. 6. 7. 8. 9. 10. 11.
Galvanometer, Inner and outer coil, Bar magnet, 1 Steel rod, Two or three 2 Ω power resistor, 25W, 10 Ω power resistor, 25W, Coil mounted on balance, 100 Ω rheostat, 25W (a rheostat is a variable resistor),
Preparation and Background Technical information and background on Experiment 6 is available in Chapters 33 and 34 of Knight. Before coming to the lab you should read the material in chapters 33 and 34 at least, then answer any questions and perform any calculations required in this preparation section. Write down any questions you have and ask them of a lab instructor during the lab period. If you do the pre-lab in advance of coming to the lab you will understand the lab better, find it easier to do, and be finished earlier.
EE1813 Lab Manual
Version 1.1
Page 53 of 102
Fundamentals of Magnetism 1.
Determine the direction of the force exerted on the conductor in Figure 6.1. Indicate the direction on the small copy of Figure 6.1 on the summary sheet.
2.
Determine the direction of forces exerted by the electromagnets in Figure 6.2 Indicate the direction on the small copy of Figure 6.2 on the summary sheet.
N
S
Figure 6.1 Force Exerted on Conductor
Figure 6.2 Force Exerted by Electromagnets
3.
A conductor moves with a constant velocity in a magnetic field in the direction shown in Figure 6.3. What is the polarity of the voltage measured at V. Indicate your answer on the small copy of Figure 6.3 on the summary sheet.
4.
What is the polarity of the voltage measured at V in Figure 6.4 when the switch, S, is suddenly closed at time t = 0? What happens to the voltage if the number of turns in the right side coil are doubled? Indicate your answer on the small copy of Figure 6.4 on the summary sheet.
+
S
V
–
N + S
V
–
Motion of Conductor
Figure 6.3 Voltage Induced on Conductor
Figure 6.4 Voltage Induced on the Secondary Coil
Experiment It is the Summary section beginning at page 58 that will be completed and submitted for evaluation. Only one report per group should be submitted. Be sure that all group members in attendance are noted at the top of the summary sheet. Important Safety Note : In this experiment you will use some power resistors and they will be carrying a large current. Be very careful not to touch these resistors as they get very hot and you Page 54 of 102
Version 1.1
EE1813 Lab Manual
Fundamentals of Magnetism could burn your fingers. For part 1 of the experiment, try to leave the power supply on for only short periods of time. The resistors may become hot enough to scorch the wood.
1. Magnet Field Produced by a Current Connect the 12 volt power supply through a long lead to two, 2-ohm power resistors in parallel. Hold the long lead away from the other leads and straight up and down. Hold the compass as close to the lead (which should be carrying about 10 amps of current), and observe the reaction of the compass needle as the compass is moved around the lead.
12V
compass 2Ω
2Ω
Figure 6.5 Probing a magnetic field around
Make two loops with the lead and place the a current carrying wire. compass in the centre of the loops. Place it above the loops, then below the loops, then beside the loops, observing the compass as you move it around the looped wires. Take a second long lead and insert it in the circuit and make a second pair of loops. Now put those loops together with the first two so the current direction is the same in both loops. Place the compass in the centre of the loops. Observe what happens. Turn one of the pairs of loops to face in the other direction. What happens then? Answer the questions in part 1 of the summary sheets.
2. Current from Motion of a Magnet Connect the galvanometer to the terminals of the outer coil. Insert the north pole of the bar magnet into the end of the coil opposite its terminals and note the polarity of the S N deflection of the galvanometer as shown in Figure 6.6 (if not marked, the North pole of + – G the magnet is painted red). Note : you will have to press and hold the galvanometer “onbutton” while making the measurement. Now Figure 6.6 Creating an Induced Voltage withdraw the north pole of the magnet and Using a Permanent Magnet in a Coil observe the effect. What is the effect of changing the speed of the bar magnet? What happens if the north pole of the magnet is inserted into the other end of the coil? Now hold the bar magnet stationary and move the coil over the bar magnet and observe the effect of changing direction and speed of the coil.
EE1813 Lab Manual
Version 1.1
Page 55 of 102
Fundamentals of Magnetism
3. Inductive Coupling of Coils
2Ω S
+
G
Connect the inner coil in series with the 2 Ω resistor, a single pole single throw (SPST) switch (this will be the switch on the power supply) and the 12V supply as shown in Figure 6.7. Carefully insert the inner coil into the outer coil. Connect a galvanometer across the terminals of the outer coil. Observe the effect of closing the switch, S, on the galvanometer reading. Now observe the effect of opening the switch on the galvanometer reading.
–
12V
Figure 6.7 Creating an Induced Voltage Using an Electromagnet in a Coil
4. Motion of Coil in Magnetic Field Connect the galvanometer to the coil mounted on the balance as shown in Figure 6.8, being sure to connect the coloured terminals correctly (red to red, black to black). The current direction in the coil and the orientation of the magnet pole faces has been indicated for you on the device. Do not, for any reason, remove or change the orientation of the magnet blocks in the horseshoe! Note that the exposed side of the coil is free to move between the poles of the horseshoe magnet. Note the deflection of the galvanometer as the coil is moved up through the magnetic field and down through the magnetic field. Verify your observations with the right hand generator rule.
G
Coil on Balance Magnet Figure 6.8 Coil on Balance with Galvanometer
5. Current-carrying Coil in Magnetic Field As indicated in Figure 6.9 on page 57, remove the galvanometer from the coil and connect the coil in a series circuit with the 5V supply, an ammeter, a 10 Ω resistor, and rheostat. Make certain that you connect the black terminal on the coil with the ground terminal on the power supply so that the current direction is correct. The rheostat may be used to adjust the current flow through the coil. Rotate the paddle so that the exposed side of the coil is directly between the poles of the magnet. Observe that a force is exerted on the coil when a current flows. What happens to the force as the current is increased and decreased? What happens if Page 56 of 102
Version 1.1
EE1813 Lab Manual
Fundamentals of Magnetism the polarity of the leads connected to the supply are reversed? Verify your observations with the left hand motor rule.
5V
10Ω
A
Coil on Balance Magnet
Figure 6.9 Coil on Balance with External Power Supply
EE1813 Lab Manual
Version 1.1
Page 57 of 102
Name(s):
ID(s):
Lab Group: Lab Day: Date:
6. SUMMARY SHEET: Fundamentals of Magnetism Answers to Preparation Questions: Mark the diagrams below in the same manner as you did in the preparation section. V
N
S
S
For Marker’s use only
34 For Marker’s use only
4
N
Motion of Conductor
Figure 5.3
Figure 5.1
V
S
Figure 5.4 Figure 5.2
For Marker’s use only
1. What happens as you move the compass around the lead carrying the current?
What happens as you place the compass in the coils of wire?
What happens when the compass is outside above the loop?
What happens when you place two pairs of loops together?
What happens when you reverse the two pairs of loops?
What do you notice about the relative strength of the earth’s magnetic field as compared to the field generated around the lead you are using?
Page 58 of 102
Version 1.1
EE1813 Lab Manual
6
Fundamentals of Magnetism 2. In Part 2 of the Experiment, what is the difference in effect on the galvanometer needle of moving the magnet out of the coil as compared to moving it in?
For Marker’s use only
6
What is the effect on the galvanometer needle of changing the speed of motion of the bar magnet?
What happens when the north pole of the bar magnet is inserted in the opposite end (the one with the terminals) of the coil? Why?
What happens when the coil moves relative to the stationary magnet? Why?
3. In Part 3 of the Experiment, describe the voltage measured with the galvanometer when the switch is pressed; describe the voltage measured when the switch is released. Explain the reason for the needle movements.
EE1813 Lab Manual
Version 1.1
Page 59 of 102
For Marker’s use only
6
Fundamentals of Magnetism 4. From Part 4 of the Experiment, carefully label the following diagram with magnet polarity, direction of conductor motion, galvanometer deflection and direction of current flow.
For Marker’s use only
8
G
Coil on Balance Magnet Figure 6.10 Coil on Balance with Galvanometer
5. From Part 5 of the Experiment, carefully label the following diagram with magnet polarity, direction of current flow and the direction of the force exerted on the conductor.
5V
10Ω
A
Coil on Balance Magnet Figure 6.11 Coil on Balance with External Power Supply
Page 60 of 102
Version 1.1
EE1813 Lab Manual
For Marker’s use only
4
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