Electromagnetic Induction

Faraday’s Law is used to

• deduce the direction of the induced current.

• deduce the magnitude of the induced e.m.f.

• explain how an induced e.m.f. is produced.

• explain how a changing magnetic field is produced.

In which of the following situations is an e.m.f. induced in a conductor?

• The conductor is connected to a battery.

• The conductor is connected to a motor.

• The conductor moves through the air.

• The conductor is moved in a magnetic field.

In the figure below, a bar magnet is pushed a short distance into a solenoid before it is pulled out. Identify the polarity induced at the end X when the bar magnet moves into and away from the solenoid.

• Magnet moves in: N , Magnet moves out: N

• Magnet moves in: N , Magnet moves out: S

• Magnet moves in: S , Magnet moves out: N

• Magnet moves in: S, Magnet moves out: S

In the figure below, a bar magnet is pushed into a solenoid. In which direction is the galvanometer needle deflected when the bar magnet passes the midpoint of the solenoid?

• It is deflected to the left.

• It is deflected to the right.

• It is deflected to the left and then to the right.

• It is not deflected.

Electricity can be generated by rotating a wire loop between the poles of a magnet. Which of the following arrangements will induce the largest current in the loop?

• The induced current is the same in all positions of the loop.

• The plane of the loop is parallel to the magnetic field.

• The plane of the loop is perpendicular to the magnetic field.

• The plane of the loop makes an angle of 45° with the magnetic field.

The figure below shows the voltage trace obtained when a source is connected to a c.r.o. The voltage gain and time base are 2 V/div and 5 ms/div respectively. What are the amplitude and period of the input source?

• Amplitude: 5 V, Period: 15 ms

• Amplitude: 5 V, Period: 30 ms

• Amplitude: 10 V, Period: 15 ms

• Amplitude: 10 V, Period: 30 ms

The voltage across the input terminals of a transformer is 110 V. The primary coil has 50 turns and the secondary coil has 120 turns. The output voltage of the transformer is

• 46 V

• 55 V

• 180 V

• 264 V

The figure below shows an ideal transformer.

Which pair of readings is possible on the meters in the secondary circuit?

• A: 1 A, V: 5 V

• A: 1 A, V: 10 V

• A: 4 A, V: 5 V

• A: 4 A, V: 10 V

A simple a.c. generator produces a voltage that varies with time, as shown below.

How will the period and maximum induced voltage change if the speed of rotation of the coil in the generator is doubled?

• Period: 5 s, Maximum voltage: 2 V

• Period: 5 s, Maximum voltage: 8 V

• Period: 20 s, Maximum voltage: 2 V

• Period: 20 s, Maximum voltage: 8 V

The electricity delivered to our homes from power stations is transmitted at high voltages and low currents because

• it is safer for engineers to repair the overhead cables.

• it is cost effective in terms of energy lost.

• electricity can travel faster along the cables.

• it reduces the resistance of the cables.