Electromagnetism

A strong electromagnet is used to attract pins.

What happens when the current in the coil is halved?

• No pins are attracted.

• Some pins are attracted, but not as many.

• The same number of pins is attracted.

• More pins are attracted.

The diagram shows a transformer.

The input voltage is 240 V.

What is the output voltage?

• 6 V

• 12 V

• 20 V

• 40 V

A coil carries a current in a magnetic field. The coil experiences a turning effect.

Which device uses this effect?

• a d.c. motor

• an electromagnet

• a relay

• a transformer

A magnet is suspended from a spring so that it can move freely inside a stationary coil. The coil is connected to a sensitive centre-zero galvanometer.

The magnet repeatedly moves slowly up and down.

What does the galvanometer show?

• a constantly changing reading

• a steady reading to the left

• a steady reading to the right

• a steady reading of zero

A transformer has 50 turns on its primary coil and 100 turns on its secondary coil. An alternating voltage of 25.0 V is connected across the primary coil.

What is the voltage across the secondary coil?

• 12.5 V

• 50.0 V

• 100 V

• 200 V

A wire is placed between the poles of a horseshoe magnet. There is a current in the wire in the direction shown, and this causes a force to act on the wire.

Three other arrangements, P, Q and R, of the wire and magnet are set up as shown.

Which arrangement or arrangements will cause a force in the same direction as the original arrangement?

• P, Q and R

• P and Q only

• P only

• R only

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 the poles of a magnet.

Which electrical device operates because of this effect?

• a battery

• a cathode-ray tube

• a generator

• a motor

The diagram shows a flat, rectangular coil placed between the poles of a magnet.

There is a current in the coil that makes it turn in the direction shown in the diagram.

Which change would make the coil turn in the opposite direction?

• decreasing the current in the coil

• increasing the number of turns on the coil

• reversing both the direction of the current in the coil and the poles of the magnet

• reversing only the direction of the current in the coil

A transformer has 1000 turns on its primary coil. An input voltage of 12 V is applied to the primary coil, and an output voltage of 120 V is induced across the secondary coil.

How many turns are on the secondary coil of the transformer?

• 100

• 120

• 1000

• 10 000