IG Revision :Electromagnetic induction

Which graph shows the output voltage from a simple a.c. generator?

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A transformer has 50 turns on its primary coil and 100 turns on its secondary coil. An a.c. voltage

of 25.0 V is connected across the primary coil.

What is the voltage across the secondary coil?

• A 12.5V

• B 50V

• C 175V

• D 200V

The diagram shows an electrical device.

What is this electrical device?

• A a d.c. motor

• B an a.c. generator

• C a magnetising coil

• D a transformer

The graph shows the voltage input to a step-down transformer.

Which diagram shows the voltage output from the transformer?

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The diagram shows an a.c. generator.As the coil passes through the position shown, the output voltage is +10 V. When does the output voltage become –10 V?

• A when the coil has turned through 90°

• B when the coil has turned through 180°

• C when the coil has turned through 270°

• D when the coil has turned through 360°

A wire is placed in a strong magnetic field. When a current is passed through the wire it moves upwards, as shown.

The current is reversed.

In which direction does the wire move?

• A downwards

• B towards the north pole

• C towards the south pole

• D upwards

The diagram shows a coil of wire between the poles of a magnet.

The coil consists of 20 turns of insulated wire.

The coil is connected to a variable resistor and a power supply. How can the turning effect on the coil be increased?

• A by moving the poles of the magnet closer to the coil

• B by reducing the number of turns on the coil while keeping the current constant

• C by increasing the resistance of the variable resistor

• D by reversing the terminals of the power supply

step-down transformer is used to light a 12 V lamp from a 240 V mains supply. The lamp lights at normal brightness. The primary coil has 600 turns.

How many turns are in the secondary coil?

• A 12

• B 20

• C 30

• D 50

When a wire is moved upwards between the poles of a magnet, an electromotive force (e.m.f.) is

induced across the ends of the wire.

Which device uses a moving wire to induce an e.m.f.?

• A a cathode-ray tube

• B a generator

• C a transformer

• D an electromagnet

he diagram shows cables used in the transmission of electrical energy. High voltages are used for the transmission.

• A Fear of high voltages stops people from interfering with the cables.

• B Heat loss in the cables is smaller than if low voltages are used.

• C High voltages increase the current in the cables.

• D High voltages produce large magnetic fields, so less insulation is needed.