physics7ar.files.wordpress.com€¦ · Web view · 2018-04-19Physics. Electromagnetism & EM...
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Name: _______________________________________________ Physics Electromagnetism & EM Induction Date: Time: Total marks available: Total marks achieved: ______
Transcript of physics7ar.files.wordpress.com€¦ · Web view · 2018-04-19Physics. Electromagnetism & EM...
Name: _______________________________________________
PhysicsElectromagnetism & EM Induction
Date:
Time: Total marks available: Total marks achieved: ______
Questions
Q1.Explain how the transmission of electrical power is made more efficient by using step-up and step-down transformers.
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(Total for question = 5 marks)
Q2.A student is listening to a radio.
(a) The radio is powered by batteries that provide a direct current (d.c.).
What is direct current?(1)
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(b) Radio waves are part of the electromagnetic spectrum.
(i) Suggest a property of radio waves that makes them suitable for use in communication.(1)
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(ii) Complete the table to show uses and possible harmful effects of some otherparts of the electromagnetic spectrum.
(4)
(c) In the radio, sound is produced by a loudspeaker.
The diagram shows the construction of a loudspeaker.
Describe how a loudspeaker uses an electrical supply to produce sound waves.(5)
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(Total for question = 11 marks)
Q3.Photograph E shows a rechargeable torch.
(a) When a student shakes the torch, the magnet moves through the coil and back again.This induces a voltage across the ends of the coil.The voltage is used to provide current to recharge the battery.
(i) Explain why a voltage is induced.(2)
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(ii) State one way to increase this voltage.(1)
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(b) Photograph F shows the components inside the torch.
The torch uses a light-emitting diode (LED) to provide light.(i) When the LED is on, it shows that
(1)
A the current is alternating
B the torch is switched off
C there is a current in the circuit
D there is a fault in the circuit
(ii) The manufacturer of the torch states, "An LED is a more efficient source of lightthan a filament lamp."
Explain this statement in terms of energy transfer.(2)
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(Total for question = 6 marks)
Q4.Many food shops have devices that attract and kill flying insects.
The devices consist of an ultraviolet lamp a plastic mesh on the outside an electrified wire grid below the plastic mesh a transformer that is connected to the wire grid
(a) The ultraviolet lamp attracts many flying insects towards the device.
Ultraviolet is an electromagnetic wave.(i) State two properties of electromagnetic waves.
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(ii) Which of these electromagnetic radiations has a frequency greater than ultraviolet?(1)
A infrared B gamma rays C radio waves D visible light
(b) The transformer supplies an output voltage of 2000 V a.c. to the wire grid.
The input voltage to the transformer is 230 V a.c.(i) Give the name of this type of transformer.
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(ii) State the relationship between input (primary) voltage, output (secondary) voltage, primary turns and secondary turns.
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(iii) There are 110 turns on the primary coil.Calculate the number of turns on the secondary coil.
(3)
number of turns ...........................................................
(iv) Suggest a reason why there is a plastic mesh on the outside of the device.(1)
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(Total for question = 9 marks)
Q5.
A wind turbine generates electricity for the National Grid.
(a) The useful energy transfer in the wind turbine is(1)
A chemical energy to electrical energy
B gravitational potential energy to electrical energy
C kinetic energy to electrical energy
D sound energy to electrical energy
(b) The generator in the wind turbine transfers 39 MJ of energy in 1 minute.The generator current is 490 A.(i) Calculate the output voltage of the generator.
(3)
Voltage = ........................................................... V
(ii) The generator output voltage is then increased to 132 kV for transmission.
Explain why electrical energy is transmitted using very high voltages.(4)
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(c) The generator provides a direct current (d.c.).This d.c. is changed to an alternating current (a.c.).The frequency of the alternating current is 50 Hz.(i) Explain the meaning of 50 Hz alternating current.
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(ii) Explain why the d.c. from the generator must be changed to a.c. before it istransmitted. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................
(Total for question = 12 marks)Q6.The diagram shows a coal-fired power station.
(a) (i) In which part of the power station is heat energy usefully converted to kineticenergy?
(1)
A boiler
B turbine
C generator
D wires
(ii) In which part of the power station is kinetic energy usefully converted toelectrical energy?
(1)
A boiler
B turbine
C generator
D wires
(b) A transformer is used to convert the 25 kV output from the power station to 115 kV.(i) State the equation linking power, voltage and current.
(1)
(ii) Compare the input current and the output current of the transformer.Assume there are no energy losses in the transformer.
(3)
(iii) State one advantage of transmitting electricity at high voltages.(1)
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(c) Some power stations use uranium as a fuel.Describe the problems that arise from the disposal of waste from this type of power station.
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(Total for question = 11 marks)Q7.A student investigates how to produce a voltage.
He hangs a magnet from a spring, above a coil that is connected to a data logger.
(a) The student pulls the magnet through the coil to X and then releases it.
The magnet moves up and down through the coil.
The data logger produces this graph of voltage against time.
(i) Explain why the data logger records a varying voltage..............................................................................................................................................
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(ii) Which feature of the graph shows that the voltage is alternating?
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(iii) Suggest why the voltage changes as shown by the graph.
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(b) The student repeats the experiment using two magnets taped together.
Compared to one magnet, these two magnets take a longer time to move up and down.
The dotted line on the grid shows the original graph for one magnet.On the same grid, sketch the graph that would be produced using two magnets.
(3)
(Total for question = 8 marks)
Q8.Magnetic field lines show the shape and direction of a magnetic field.
(a) The diagram shows a cross-section through a wire placed between two magnetic poles.
The wire carries electric current into the page at X. The shape of the magnetic field is shown.
(i) Add arrows to two of the magnetic field lines to show the direction of the magnetic field.(1)
(ii) Draw an arrow on the diagram to show the direction of the force on the wire.Label this arrow F.
(b) The wire is removed and the magnetic field between the poles changes.Sketch the new magnetic field.
(2)
(c) Explain how you could use a plotting compass to investigate the magnetic field around a bar magnet.
You may draw a diagram to help your answer.(3)
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(Total for question = 8 marks) Q9.This photograph shows an electromagnetic device used to keep a door open.
The electromagnet attracts the metal plate to hold the door open.
The electromagnet is connected to a fire alarm circuit.
When the fire alarm sounds, the door is released and it closes.
(a) State why the metal plate is made of iron.
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(b) Describe the construction of an electromagnet.
You may draw a diagram to help your answer.(3)
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(c) Describe the changes that allow the electromagnet to release the door when the fire alarm sounds.
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(Total for question = 6 marks) Q10.Diagram 1 shows some of the apparatus used to investigate the force on a current-carrying wire, XY, in a magnetic field.
(a) Diagram 2 shows the poles of the magnet viewed from above.
Draw the uniform magnetic field between the poles.(2)
(b) The current-carrying wire XY is at right angles to the magnetic field.
The current in the wire is 10 A.(i) Suggest why the wire used in this investigation must be thick.
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(ii) Explain why the wire XY experiences a force when there is a current in the circuit.(3)
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(iii) State two ways in which this force can be reduced.(2)
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(Total for question = 8 marks) Q11.(a) State what is meant by the term magnetic field line.
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(b) The diagram shows a cross-section through a wire placed between two magnetic poles.
The wire carries electric current into the page at X.
The shape of the magnetic field is shown.
(i) Add arrows to any two lines to show the direction of the magnetic field.(1)
(ii) Draw an arrow on the diagram to show the direction of the force on the wire.Label this arrow F.
(2)(c) Describe the magnetic field in the region inside the dotted square.
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(Total for question = 6 marks)Q12.This question is about magnetic fields.
(a) Describe an investigation to show the shape of the magnetic field for a permanent bar magnet.
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(b) The diagram shows a bar magnet.
Draw the magnetic field pattern of the bar magnet.
(c) A student uses two bar magnets to create a uniform magnetic field.
She places a current-carrying wire at right angles to the magnetic field, as shown in the diagram.
(i) The student observes that the wire experiences a force.What is the direction of the force on the wire?
(1) A to the left B to the right C out of the page D into the page
(ii) State two changes, each of which would reverse the direction of the force.(2)
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(iii) The student moves the bar magnets further apart.Explain what effect this would have on the force on the wire.
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(Total for question = 11 marks)
Q13.The photograph shows a simple d.c. electric motor.
(a) When the switch is closed the coil spins.Explain why this happens.
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(b) (i) Describe two ways to increase the speed of rotation of the coil in this motor.(2)
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(ii) Suggest how to make the coil spin in the opposite direction.(1)
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(c) In a different motor, the magnets are curved and there is a piece of iron inside thecoil. The iron increases the strength of the magnetic field through the coil.
Suggest how the curved magnets and the piece of iron improve the performanceof the electric motor.
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(Total for question = 8 marks)Q14.Some students are investigating a simple electric motor.
(a) When the switch is closed the coil spins on the axle.State why.
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(b) State two changes that would make the motor spin faster.(2)
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..............................................................................................................................................(c) The students change their circuit, replacing the cell and switch with a lamp.
When they spin the coil by hand, the lamp lights.Explain why the lamp lights.(2)
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(Total for question = 6 marks)Q15.(a) A direct current passes around a flat, circular coil as shown.
On the diagram, sketch the magnetic field caused by the current in the coil.(3)
(b) The coil is suspended vertically so that it is free to swing.
A second, identical coil is placed beside it.When direct currents pass, as shown, the two coils move together.
When the current in the right-hand coil is reversed, the two coils move apart.
Explain why the coils move in this way.(3)
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(Total for question = 6 marks) Q16.The diagram shows a piece of card and two wide bar magnets.
(a) (i) Add to the diagram to show the shape and direction of the magnetic fieldpattern between the magnets.
(3)(ii) Describe how to investigate the shape and direction of the magnetic fieldbetween the magnets.
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(b) A metal rod, X Y, is placed in a magnetic field as shown.
Wires from a cell are connected to the ends of the rod so that there is a currentfrom X to Y.
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(Total for question = 8 marks)Q17.A laptop battery charger contains a step-down transformer.
(a) The number of turns on the primary coil of a step-down transformer is(1)
A the same as the number of secondary turns
B more than the number of secondary turns
C less than the number of secondary turns
D zero
(b) This transformer is designed to reduce the voltage from 230 V to 12 V.
The primary current is 0.25 A.(i) State the equation linking primary voltage, primary current, secondary voltageand secondary current for a transformer.
(1)
(ii) Calculate the secondary current, assuming that the transformer is 100% efficient.(2)
Secondary current = ........................................................... A
(c) A student notices that the charger becomes warm when it is working.Suggest how this will affect the output of the transformer.
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(Total for question = 6 marks)Q18.The diagram shows a transformer that is 100% efficient.
(a) (i) State the equation linking input power and output power for the transformer.
(1)
(ii) State the equation linking input power and output power for the transformer.(2)
output current = ........................................................... A
(b) (i) State the equation linking input voltage, output voltage and turns ratio for the transformer.
(1)
(ii) Calculate the number of turns on the secondary coil of the transformer.(2)
number of turns = ...........................................................
(c) Explain how a transformer works.
In your answer, you should include the reasons for using two coils an iron core an alternating supply
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(Total for question = 11 marks)
Q19.Electrical energy can be transmitted using a high voltage of 132 kV.
(a) A voltage of 132 kV is the same as
(1)
A 132 V
B 1320 V
C 132 000 V
D 132 000 000 V
(b) Using a high voltage increases the
(1)
A current in the wires
B efficiency of transmission
C energy lost as heat
D resistance of the wires
(c) The high voltage can be reduced using a
(1)
A generator
B magnet
C transformer
D transmitter
(Total for question = 3 marks)
Q20.The diagram shows a magnet held above a coil. The coil is connected to a voltmeter.
(a) The magnet is released and falls into the coil.(i) Explain why the voltmeter shows a reading.
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(ii) The magnet is released from a greater height.How does this affect the voltmeter?Explain your answer.
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(b) State how the voltmeter reading changes when the same magnet(i) moves more slowly into the coil
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(ii) moves into a coil with more turns(1)
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(iii) is reversed so that the S-pole enters the coil first.(1)
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(Total for question = 7 marks)
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