Miscellaneous

Question 1

Name the particles whose movement can cause static charge to build up

Answer 1

Electrons

Question 2

Strength of Earths magnetic field

Answer 2

0.01mT

Question 3

Strength of MRI scanners electromagnet

Answer 3

10T

Question 4

What type of current must be supplied to a loudspeaker for it to work?

Answer 4

Alternating current

Question 5

Give two ways you can reverse the direction of a basic d.c. motor

Answer 5

• Reverse the current
• Swap the magnetic poles over

Question 6

Explain how a split ring commutator keeps an electric motor rotating in the same direction.

Answer 6

It swaps the contacts every half turn, so the left hand and the right hand arms of the coil always experience a force in the same direction.

Question 7

A loudspeaker contains a coil of wire in a magnetic field. Explain how a loudspeaker creates sound waves when an alternating current is supplied to it.

Answer 7

When current is supplied to a coil, the coil feels a force that moves it in one direction. When the current flows in the opposite direction, the coil will experience a force in the opposite direction. As a.c. is being supplied to the coil, th direction of the current (and therefore the direction of the force) keeps changing. This makes the coil move back and forth. The coil is attached to the cone, so the cone vibrates, creating sound waves.

Question 8

What is meant by the term ‘electromagnetic induction’?

Answer 8

When a potential difference is induced across a conductor when if experiences a change in an external magnetic field.

Question 9

Describe how a potential difference in a wire can be induced using a magnetic field.

Answer 9

Move the wire relative to the magnetic field, or change the magnetic field the wire is in.

Question 10

A student induces a potential difference across a wire using a magnet. Explain why this potential difference may not produce a current in the wire.

Answer 10

The wire may not be part of a complete circuit, which is needed for current to flow.