6 2 electromagnetic induction

Electromagnetic induction is the effect of inducing e.m.f. in a conductor due to the relative motion between a conductor and a magnetic field.

A voltage can be induced in a wire by moving it through a magnetic field.

False. A voltage can also be induced by placing a stationary conductor in a changing magnetic field.

The direction of an induced e.m.f. can be reversed by:

False. When the north pole of a bar magnet is pushed towards a coil, the end of the coil begins to act as a north pole. As a result, the two like poles repel in order to oppose the motion of the magnet.

The size of the induced potential difference in the wire in the diagram is determined by:

The size of the induced potential difference in the coil in the diagram is determined by:

An A.C. generator is a device which converts energy from a mechanical store to an electrical store.

The output of an A.C. generator is alternating current.

A simple A.C. generator consists of:

The purpose of slip rings is to provide a connection between the rotating coil and the external circuit.

The direction of the current reverses every half rotation of the coil in the A.C. generator.

False. A maximum value of current is induced when the coil is perpendicular to the magnetic field.

True. No current is induced when the coil is parallel to the field.

For an A.C. generator, the shape of the graph of output current against time is a sine or cosine curve.

The frequency of an A.C. output is the number of complete cycles it makes each second e.g. 1 cycle per second = 1 Hz.

In an A.C. generator, the size of the induced current can be increased by:

The function of a transformer is to change the value of an alternating potential difference or current.

A simple transformer consists of:

A step-up transformer increases the potential difference of a power source.

A step-down transformer decreases the potential difference of a power source.

True. When an alternating current is supplied to the primary coil of a transformer, it produces a changing magnetic field in the iron core.

False. A step-down transformer has fewer turns on the secondary coil than the primary coil.

True. When a changing magnetic field is produced in the iron core of a transformer, it induces a changing potential difference in the secondary coil.

A step-down transformer has fewer turns on the primary coil than the secondary coil.

A step-up transformer has fewer turns on the primary coil than the secondary coil.

True. To increase potential difference, a step-up transformer must have more turns on the secondary coil than on the primary coil.

The type of transformer in the diagram is a step-down transformer.

The primary voltage of the transformer in the diagram is 300 V.

The purpose of transformer calculations is to determine the output potential difference (voltage) of a transformer based on:

True. The equation for the ratio of potential differences across the primary and secondary coils of a transformer is .

The equation for calculating the output potential difference of a transformer is Where: