Unit 9: Electromagnetic induction, generators and transformers

• 6.0 V

• 12 V

• 20 V

• 40 V

Which device uses a split-ring commutator?

• a d.c. motor

• a relay

• a transformer

• an a.c.. generator

Electrical power is transmitted at 400 kV and transformed down to 240 V before being delivered to consumers.

Which statement is correct?

• A 400 kV cable requires less insulation than a 240 V cable.

• Birds are subject to a high-voltage shock when resting on high-voltage cable.

• The current in the transmission wires is equal to the current delivered to the consumers.

• With a 400 kV transmission system, a smaller proportion of the energy is used to heat the atmosphere than with a 240 V system.

• A

• B

• C

• D

A step-down transformer is 100% efficient. It has an input voltage of 240 V a.c. and an output voltage of 60 V a.c.

The current in the primary coil is 0.50 A.

What is the current in the secondary coil?

• 0.13 A

• 0.50 A

• 2.0 A

• 8.0 A

• A

• B

• C

• D

• 0.050 A

• 0.20 A

• 5.0 A

• 20 A

• A

• B

• C

• D

What is an advantage of transmitting electricity at a high-voltage?

• It is faster

• It is safer

• Less energy is wasted

• Less equipment is needed

An e.m.f. is induced across a wire when it moves through the magnetic field between two poles of a magnet.

Which electrical device operates because of this effect?

• A battery

• A cathode-ray tube (electron tube)

• A generator

• A motor