Explain At Ion

Form 4-Explaination Chapter 2: Force and Motion Implusive Force In two separate boxing ring, a kick-boxer Thailand fights without wearing boxing gloves whereas a boxer from Malaysia fights with a pair of boxing gloves. Explain who will cause more injury to their opponent if both boxers punch with the same force. (3 marks) Answer: Thai boxer Without wearing boxing gloves, the time for change momentum is shorter. The impulsive force is larger. Gravitational Force Explain why it is easier to walk on a rough surface than on an oily surface (4 marks) Answer: A rough surface produce more friction. Therefore better grip and less slipping between the soles and the surface. Thus easier to walk. An oily surface reduces contact between the soles and the surface no opposing force will act Therefore difficult to walk. Energy A stone which released from a tall building falls down in the air. During the fall, the stone experiences an energy change. Explain the energy changes in the stone. (4 marks) Answer: Total energy at any time is constant As the stone falls, gravitational potential energy convert to kinetic energy Gravitational potential is maximum at the highest point Kinetic energy converts to heat and sound when it hits the ground. Elasticity Explain how the forces between the molecules cause the elasticity Answer: The forces between the molecules are attractive forces and repulsive forces

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When the solid is stretched, the molecules to be displaced away from each other Attractive intermolecular forces act to oppose the stretching When the solid is compressed, the molecules are being displaced closer to each other. Repulsive forces are acting to oppose the compression.

Chapter 3: Force and Pressure Atmospheric pressure Explain why places at high altitude the temperature is colder compare to places at low altitude which is more warmer. Answer: high altitude low density of air less collision of molecules with surface

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low altitude high density of air more collision of molecules with surface if more collision of molecules with surface, heat energy are more produced. So that low collision is more warmer.

Pressure in Liquid A small bubble of air is released from the bottom of a lake. (i)

Explain what happens to the size of bubble as it rises to the surface of the water. [2 marks]

(ii)

Explain how this change affects the upward motion of the bubble. [2 marks]

Answer: (i) - The pressure of water increases with the depth of the water - The bubble expands upon reaching the surface of the water//The volume of air bubble increases as the depth of water decreases (ii) - Buoyant force increases as the volume of the bubble increases - The air bubble moving with increasing acceleration Siphon Explain how a siphon works to transfer liquid from one container to another. (4 marks) Answer: The siphon works based on pressure difference Air pressure in the inner tube is less than the atmospheric pressure outside the tube. The atmospheric pressure pushes the surface of liquid Causes the liquid to flow into the column of the tube. (to the other side of the tube into the other container) Buoyant Force

1. Explain why the balloon and the load remain suspended? Answer: The buoyant force is equal in magnitude but opposite in direction to weight of balloon and load. The resultant force = 0 The balloon and load are in equilibrium

Rod A Water

Rod B Water

Answer: -

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B is denser than A. Weight of B is greater than weight of A Weight of water displaced by B is greater

3. Explain why a ship may sink when it sails from sea water to fresh water. ( 3 marks) Answer: 1. In the sea, buoyant force > weight of the ship 2. When the ship in the river, density of water< density of sea, so buoyant force decrease 3. The weight of the ship > the buoyant force ,so the ship will sink 4. Explain why a balloon filled with helium gas rises up in the air. (4 marks) Answer: The balloon acted by two forces: upthrust and the weight of the balloon The density of helium gas is less than the density of surrounding air.

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Upthrust equal to the weight of the air displaced by the balloon

Upthrust is higher than the weight of the balloon. 5. Explain why the sinking levels of the boats are different in the river and in the sea. [3 marks] Answer: - Sea water is denser - Boat displaced less sea water and gain the same upthrust . - Therefore boat sinks less in sea water 6. The submarine is able to submerge in the sea. Explain how a submarine on the sea surface submerges and float still on the sea surface. Answer: - When the ballast tank is filled with water, - The buoyant force is smaller than the weight of the submarine. It will sink/submerges - When the ballast tank is filled with air / when the water pumps out, - the buoyant force is larger than the weight of the submarine, and it will float. Hydrometer A hydromater is used to measure the density of acid a car battery. Using a suitable physisc principle, explain how the hyromater works. (4marks) Answer: related principle is the Archimedes’ Principle. Draw a diagram of hyrometer correctly ( small and long stem, with big bulb with lead or steell balls) When a hydromater floats in a liquid, the buoyant force is equal to the weight of the hydromater

2.Diagram 11.2 shows rod A and rod B of different densities are immersed in water. Explain why the rods float in water and why B sinks deeper than A. [4 marks]

Both A and B float because their densities are less then water//weight of rod A and B equals the weight of water displaced.

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Bouyant force = ρVg / depends on density of liquid The smalleer the density of the liquid, the more liquid it displaces and the deeper the hydromater will sink

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Bernoulli Principle The aircraft obtains its lift when flying due to a difference in pressure of the air between the upper and bottom sides of the wings. Explain how this difference in pressure is produced. [3 marks] Answer: - The shape of cross section of the wing causes the speed of airflow - Above the wings to be higher than the speed of airflow below - When the speed of moving air is higher, the pressure is lower - Hence air pressure below the wings is higher compare to above the wings Pascal Principle Using a concept of pressure in liquid, explain why the hydraulic system in this machine is known as a force multiplier. (4 marks) Answer: 1. When the small piston is pulled up, the hydraulic oil is drawn from the reservoir into the small piston 2. When the small piston is pushed down , the hydraulic oil is exerted with force and experienced a pressure 3. The pressure is transmitted uniformly from the small piston to the bigpiston. 4. The forced produced raised the big piston / The system can convert a small input force into a bigger output force. Chapter 4: Heat Thermal equilibrium 1. Explain how a new thermometer can be calibrated. [4 marks] Answer: - Put the thermometer in melting ice, mark the lower part of mercury thread,l0 - Place the same thermometer in the boiling water, mark the top part of the mercury thread, l 100 - Divide the length between the two marks into 100 equal divisions - Each division is now equal to 1 o C 2. According to the principle of thermal equilibrium and the working principle of a thermometer, explain how a doctor can check his patient temperature during medical treatment. [ 4 mark ] Answer: - Thermometer is placed in the mouth of patient, - Heat is transferred from patient’s body to the thermometer. - Thermal equilibrium between the thermometer and patient’s body is reached when the net rate of heat transfer is zero. - The thermometer and the patient’s body are at the same temperature. The thermometer reading shows the temperature of the patient’s body. Specific heat capacity

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Explain why water is normally used as a cooling agent or cooling system in a car engine radiator. ( 4 marks) Answer: - It doesn’t react to the inner part of the engine - it take a long time to heat up water because high specific heat capacity

- can absorb large amount of heat energy - cheap and easily available Specific Latent Heat (i) Your body sweats when you are feeling hot. How does sweating helps to cool down your body? [ 2 marks ] (ii) Explain why a scald from steam is more serious than the one from boiling water? [ 2 marks ] Answer: (i) - Water evaporates from the skin when we sweat. - for water to evaporate it use heat from the body (ii) - Steam has more heat than boiling water - due to latent heat of vaporization A student standing near the beach could feel the cool breeze from the sea on a hot day. Explain how the cool breeze from the sea occurs. [3 marks ] Answer: The increase in temperature for land is higher The air above land is heated up Cooler air from the sea moves towards land Chapter 5:Light Reflection of light Figure 11.1 shows the top view position of a car driver, the car’s side mirror and the front of a lorry which is overtaking the car.

the fish appear to be closer to the surface than a actual is While driving a car on a hot day, you may see a mirage on the road. Explain how mirage occurred. [ 4 marks ] Answer: - The layers of air nearer the road warmer. - The density of air decrease nearer to the road surface. - The light travel from denser (cold) to less dense (hot) area. - The light refract away from the normal - When the angle of incidence exceed the critical angle, total internal reflection occurs. - near the road surface, the angle of incidence exceeds / greater than the critical angle. - total internal reflection occurs and light bends towards the eye of the observer.

Optical Fibre (ii) With the help of a diagram, explain the working principle of an optical fibre. [4 marks] Answer: -

Diagram shows a curved optical fibre (with outer and internal layer) with at least two total internal reflection The refractive index of the internal layer of the optical fibre is greater than that of the external layer or air

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(i) Name the type of mirror used for the side mirror in Figure. [ 1 marks ] (ii) Explain why the mirror in Figure is used not of other types of mirror. [ 3 marks ] Answer: (i) Convex mirror (ii) – has a wider view - upright image - the image is seem at a distance v ≤ f behind the mirror for all positions of the object. Refraction of light Figure below shows a pear which was thrown by a fisherman towards a fish in a pool.

Given that the spear did not hit the fish, explain the observation. (3 marks)

Angle of incidence, i > critical angle, c Total internal reflection occur Describe how you estimate the focal length of a convex lens. [4 marks] Answer: - The convex lens with its holder is aimed at a distant object like a tree. - Adjust a screen until you see a very sharp and clear image of the distant object. - When parallel light rays from a distant object pass through a convex lens, they will converge to a point called focal point/ label on a diagram - Measure the distance between the convex lens and screen./ label on a diagram Form 5 Chapter 1:Wave Refraction of wave Explain why the wavefronts in the sea follow the shape of the coastline as the water becomes shallower. ( 4 marks ). Answer: - At the centre of the ocean the water waves travel at uniform speed as the depth of the sea is uniform - When the waves reached the coast ,the water is shallower, wave speed refraction occurs - Refraction causes the wavefront bend toward the normal - This results the wavefront following the shape of coastline Sound wave

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1. Discuss how you would use sound waves to determine the depth of the sea. (3 marks) Answer: Sonar waves / ultrasound are sent down form a ship towards the bottom of the sea. The waved reflected from the sea bed is detected at the ship The time taken, t, for the sonar to go down and come back to the ship is measured. The depth of he sea, D, from the ship to the sea bed is calculated as follows: D = ½ vt where v is the speed of sonar waves in sea water.

ocean

beach

2. Water waves always follow the shape of the beach as the waves approach the beach. Explain (i) What happens to the speed and wavelength of waves while the waves is in middle of the sea and when the waves approach the beach. (ii) Why the water in the bay stationary compared to the water at the cape. [6 marks] Answer: i. -The depth of water decreases toward the beach -Refraction of water waves occurs . -The velocity and wavelength of the water waves approach the shallower beach ii. The depth of water increase Energy spread away Amplitude become smaller

3. In daily life we find sounds can be heard more clearly at night than in the day. Explain this observation and state two factors that affect the speed of sound in air. [6 marks] Answer: • At night ,the layers of air near the ground are cooler compared to the upper layers of air. • Sound travels at a lower speed in cool air • Its refracted away from the normal as pass through warmer air • The sound waves are refracted in a downward curve towards the ground instead of disappearing into the upper layers of air. • The two factors are air temperature and density • This occurrence is due to the refraction of the sound waves. Resonance

Explain why strong double-glazed glass is used as walls of the observation tower in an airport. (4 marks) Answer: All particles in a material/matter/glass vibrate at its natural frequency The airplane engine produces noise which cause the air to vibrate Due to resonance, the glass particles vibrate at higher / maximum amplitude Need strong glasses to withstand the effect of resonance/ the strong vibration/ high amplitude so that it does not break easily. Chapter 2: Electric 1. Explain why it is more dangerous to touch the live wire of a mains supply, rather than the neutral wire. [4 marks] Answer: - Our bodies are at earth potential (0V) - If we touch the live wire, there will be a large potential difference (p.d) the live wire and our body. A large current flow through it, probably fatal. - The neutral wire stays at earth potential (0V), roughly at the same potential as our body. - If we touch the neutral wire, there is no p.d. across us and so no current flows

2. Explain why the bulb connected to two dry cells is brighter Answer: Each cell has internal resistance When two cells are connected in parallel, the resultant internal resistance is smaller. Less voltage is lost when cells in parallel are used The external circuit will get more voltage. Thus the bulb is brighter 3. Figure shows the burning candle placed between a pair of parallel metal plates. What will happen to the candle flame when the extra high voltage supply (E.H.T) is switch on? Explain your answer. (4 marks)

Answer: -

The lighted candle/the heat from the candle causes the air molecules (surrounding) to be ionized The positive charges would be attracted to the negative plate and / or the negative charges would be attracted to the positive plate The flame of the candle would be dispersed (flattened) into top parts More the flame is attracted to the negative plate

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Positive charges are heavier than negative charges

PARALLEL CIRCUIT Explain the advantages of connecting household appliances in parallel. [4 marks] ANSWER The current through each electrical appliance is higher//The bulbs in the parallel circuit light up brighter compared to the same bulbs in series circuit// Effective resistance is much smaller when connected in parallel circuit If any devices/components broke down, others can still be used The circuit breaker / fuse can be connected to each path for safety Only certain devices that are not in use can be switched off. The current can still flow through the other path GRID NATIONAL Explain three advantages of the national grid network. (3 marks) Answer: no disruption of power supply when a station breaks down efficient power generation during low peak period certain stations can be shut down power station can take turns to shut down for repair and services. Chapter 3: ELECTROMAGNET 1. Explain why the strength of the magnetic field is greater at the center of coil. [3 marks] Answer: - The direction of the magnetic field on the left coil is counter/anti clockwise,/diagram - The direction of the magnetic field on the right coil is clockwise // diagram

- As the result the magnetic fields in the middle of the coil are in the same direction, upward. So the magnetic field will be stronger in the middle 2. Diagram shows a simple electromagnet. Two magnet are hung freely.

Explain what happen to magnet P and magnet Q when the switch is on. (4 marks) Answer: When the switch is on, the soft iron core becomes electromagnet. End A becomes north pole and end B becomes south pole Magnet P repels from end A Magnet Q attracts to end B

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(ii)

3. Explain how the electric bell function. (4 marks) Answer: when the switch is on, current flows in the solenoid, soft iron core becomes electromagnet. Electromagnet attracts the iron armature, the hammer hits the gong and bell rings When the hammer mover towards the gong, the contacts open, current stop flowing The iron core loses its magnetic. 4. Diagram 10.4 shows a d.c. electric motor .

. Diagram 10.4 (i) Explain how the motor is able to rotate. [4 marks] Answer: - When the current flow into the coil, magnetic field is produced. And forces are produced - Catapult field is produced - The forces are in the opposite direction - These pair of forces produce the turning effect on the coil.

5. Diagram 10.3 shows a direct current generator

Diagram 10.3 Explain how the above generator works to produce direct current. [4 marks] Answer: - rotate the coil in clock wise direction - the coil cut across the magnetic field - current is induced in the coil - the commuator change the direction in the coil so that the direction of current in external circuit I always the same. 6. Diagram 10.3 shows two thin copper strips, WX and YZ, connected to a circuit.

Explain what happen to copper strip WX and YZ when the switch is on. [4marks] Answer: electric current flow trough copper strips from ZY to WX magnetic field produced in the copper strips when the current flows the direction of the magnetic fields is same the copper rods repel to each other// the copper rods bent. 7. You are given two coils R and S, with 50 and 100 turns respectively, an iron core and a 240V a.c. power supply. All the materials are used to build a simple transformer. (i) Using all the materials supplied and with the aid of a labeled diagram(s), explain how you are going to build a simple step-up transformer. [ 4 marks ] Answer: draw and label diagram correctly iron core input 240 a.c primary coils (50 turns) secondary coil (100 turns)

8. Explain the working principle of a transformer. Answer: - When a.c. voltage is supplied to primary coil, alternating current will flow. - The soft iron core is magnetized. - The magnet produced varies in magnitude and direction. - This causes a changing magnetic flux pass through the secondary coil. - An induced e.m.f. across the secondary coil is produced Chapter 4: ELECTRONIK

1. (i) (ii) Answer: (i)

Based on diagram, which bulb will light up? Explain how the bulb will light up. Diagram 12.2

– When the potential difference supplied by the dry cell exceeds the junction voltage (barrier potential), a large current flows through the diode. The deplection layer is narrow, and the resistance of the diode is small 2. Electron in the n-type semiconductor are attracted to the positive terminal (the holes in the p-type semiconductor are attracted to the negative terminal) resulting in an electron current flow from the n-type to the p-type semiconductor. Explain how an n-type semiconductor is produce Answer: silicon crystal is doped with pentavalent atoms a free electron is available as a charge carrier. Chapter 5: Radioactivity 1. What is nuclear fission and nuclear fusion? Explain how these two nuclear reactions are able to release energy? [4 marks] ANSWER - The splitting of a heavy nucleus into two lighter nuclei - the combining of two lighter nuclei to form a heavy nucleus - The resulting nucleus (nuclei) formed has a smaller mass than the original nucleus (nuclei) - The mass defect caused energy to be released (resulting in a more stable nucleus (nuclei)) 2. Sketch a graph of activity against time to illustrate the decay rate of a radioactive substance. Use your graph to explain how the half-life is determined. (4 marks) Answer: label the axes and unit correctly draw the shape of decay curve correctl

3. Carbon-14 is a radioisotope. Explain how Carbon-14 can be used to estimate the age of a dead plant, which contain carbon. [3 marks] Answer: – Carbon-14 atom is a radioactive substance which is easily absorbed by living plants. - after the plants dies, the activity of Carbon-14 will decline since no new carbon-14 is absorbed. - by calculating the activity of carbon-14, the age of the fossil/object can be determined 4. Radioisotope Strontium-90 is used to measure the thickness of paper in a paper industry . Explain how Strontium-90 is used to measure the thickness piece of paper? Answer: - Put the radioactive source opposite the detector - Detector is connected to the thickness indicator - Detector detect the reading of the changes in counts

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- Thickness is measured with the thickness indicator - If the reading of the detector is less than the specified value, the thickness of the paper is too tick/ vice versa

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