P7

Question 1

What effect do loudspeakers use?

Answer 1

motor effect

Question 2

Explain how a loudspeaker works

Answer 2

current creates a magnetic field (around the coil)
(which) interacts with the permanent magnet field
producing a (resultant) force causing the coil/cone to move
(when the) direction of the current reverses, the direction of the (resultant) force reverses (producing a sound wave)

Question 3

How do you use Flemings left hand rule?

Answer 3

hold thumb first finger and second finger (of left hand) at right angles to each other
second finger represents the current pointing out of the paper
first finger represents the field pointing downwards
thumb points in the direction of the force / thrust / acceleration

Question 4

Suggest two changes to increase force on a rod

Answer 4

increase the current/pd
use a magnet with a greater flux density

Question 5

Describe the motion of the coil until it comes to rest in a motor

Answer 5

Resultant force experienced by coil so moves clockwise/anticlockwise where it oscillates and rests at 90 degrees to field

Question 6

When is there no force experienced

Answer 6

Wire is parallel to field

Question 7

State two other ways in which the maximum induced potential difference could be increased.

Answer 7

increase speed of coil strengthen magnetic field

Question 8

2 ways to increase force

Answer 8

• increase the current (in the solenoid / circuit)
• add more turns to the solenoid

Question 9

The handle of the alternator is turned, causing the coil to rotate.

Explain why an alternating current is induced in the coil

Answer 9

• the coil cuts magnetic field lines
• a potential difference is induced (across the coil)
• there is a complete circuit, so a current is induced (in the coil)
• every half turn the potential difference reverses direction
• so (every half turn) the current changes direction

Question 10

How do you change from dynamo to alternator?

Answer 10

Switch slip ring commutators with slip rings