magnets

Question 1

give one reason why steel is a good material for making bar magnets (1)

Answer 1

steel is a magnetically hard material

Question 2

explain how diagram 1 shows a uniform magnetic field (2)

Answer 2

• lines are evenly spaced
• lines are straight
• lines are parallel

Question 3

diagram 2 shows a metal wire being moved downwards through the uniform field between the poles of the same bar magnets. The orientation of magnets hasn’t been changed

give a reason why a voltage is induced between the ends of the metal wire as it moves between the poles of the bar magnets (1)

Answer 3

the wire cuts magnetic field lines

Question 4

state two changes that could be made to this arrangments (f3) that would increase the magnitude of the induced voltage (2)

Answer 4

1) move wire faster
2) move magnets closer together

Question 5

what is meant by the term magnetically hard (2)

Answer 5

1) difficult to magnetise
2) difficult to demagnetise

Question 6

describe how two magnets can be arranged to produce a uniform magnetic field (2)

Answer 6

• two magnets with opposite poles facing
• poles brought close to eachother

Question 7

the diagram shows a wire in a uniform magnetic field. The wire is moved up and down repeatedly in the magnetic field

explain the effect that this movement has on the ammeter reading (3)

Answer 7

1) ammeter displays a current
2) because a voltage is induced
3) induced voltage gives a current

Question 8

explain the effects on the ammeter reading of moving the wire with the same amplitude but at a higher frequency (4)

Answer 8

1) ammeter reading is greater than before
2) because wire is moving quicker
3) more field lines cut
4) gives a larger induced voltage

Question 9

explain why the compass needles turn when the current is switched on (2)

Answer 9

1) the current provides a magnetic field
2) magnets in a magnetic field line experience a force

Question 10

when a wire is moved, a current is detected.
Explain which direction the wire is moved in the magnetic field to produce current in the wire

Answer 10

• the wire is moved up
• to undergo the process of cutting field lines

Question 11

explain why a current is produced in the wire when the wire is moved in the magnetic field (2)

Answer 11

• cutting field lines induces a voltage across the wire
• complete circuit so voltage gives a current

Question 12

explain why the voltmeter reading changes from zero when the magnet is moved near the loop of wire (2)

Answer 12

• the wire cuts the field lines
• there is an induced voltage

Question 13

explain one method of increasing the magnitude of the magnetic force on the wire (2)

Answer 13

• increase the current
• increasing the voltage of power supply

Question 14

explain how the circuit could be changed to make the wire vibrate (2)

Answer 14

• use ac rather than dc
• since alternating current has changing current direction