# Chapter 25: Electromagnetic Induction

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• 1.
When there is a change in the magnetic field in a closed loop of wire
• A.

a voltage is induced in the wire.

• B.

A current is created in the loop of wire.

• C.

Electromagnetic induction occurs.

• D.

All of these

• E.

None of these

• 2.
Thrust a magnet into a coil of wire and the coil
• A.

Becomes an electromagnet.

• B.

Has a current in it.

• C.

Both of these

• D.

Neither of these

• 3.
When a bar magnet is thrust into a coil of copper wire, the coil tends to
• A.

Attract the magnet as it enters.

• B.

Repel the magnet as it enters.

• C.

Both of these

• D.

Neither of these

• 4.
Electromagnetic induction occurs in a coil when there is a change in
• A.

Electric field intensity in the coil.

• B.

Magnetic field intensity in the coil.

• C.

Voltage in the coil.

• D.

The coil's polarity.

• E.

Electromagnetic polarity.

• 5.
Voltage can be induced in a wire by
• A.

Moving the wire near a magnet.

• B.

Moving a magnet near the wire.

• C.

Changing the current in a nearby wire.

• D.

Choices A, B, and C are all true.

• E.

None of the above choices are true.

• 6.
A wire moving at right angles to a magnetic field has NO induced voltage
• A.

If it is made of copper.

• B.

If it is moving slowly.

• C.

If it is moving very fast.

• D.

If the wire is covered with insulation.

• E.

None of the above choices are correct.

• 7.
The magnetic field strength inside a current-carrying coil will be greater if the coil encloses a
• A.

Vacuum.

• B.

Wooden rod.

• C.

Glass rod.

• D.

Rod of iron.

• E.

None of these

• 8.
If a magnet is pushed into a coil, voltage is induced across the coil. If the same magnet is pushed into a coil with twice the number of loops
• A.

One half as much voltage is induced.

• B.

The same voltage is induced.

• C.

Twice as much voltage is induced.

• D.

Four times as much voltage is induced.

• E.

None of these

• 9.
An electric motor is very similar to
• A.

An electric generator.

• B.

An automobile battery.

• C.

• D.

None of the above choices are correct.

• 10.
A device that transforms electrical energy to mechanical energy is a
• A.

Generator.

• B.

Motor.

• C.

Transformer.

• D.

Magnet.

• E.

None of these

• 11.
A device that transforms mechanical energy into electrical energy is a
• A.

Generator.

• B.

Motor.

• C.

Transformer.

• D.

Magnet.

• E.

None of these

• 12.
If the voltage produced by a generator alternates, it does so because
• A.

Unlike a battery, it produces alternating current.

• B.

The changing magnetic field that produces it alternates.

• C.

Alterations in the mechanical energy input.

• D.

In effect it is an ac motor in reverse.

• E.

The current it produces alternates.

• 13.
A principle difference between an MHD generator and a conventional generator is that the MHD generator
• A.

Has no moving parts.

• B.

Operates more efficiently at high temperatures.

• C.

Choices A and B are both true.

• D.

Choices A and B are both false.

• 14.
A transformer actually transforms
• A.

Voltage.

• B.

Magnetic field lines.

• C.

Generators into motors.

• D.

Non-safe forms of energy to safe forms of energy.

• E.

All of the above choices are correct.

• 15.
The primary of a transformer is the coil connected to
• A.

• B.

The Internet.

• C.

The power line.

• D.

None of these

• 16.
Transformers use ac so there will be the required
• A.

Transfer of energy from coil to coil.

• B.

Voltage for transformation.

• C.

Change in magnetic field for operation.

• D.

Change in input current.

• E.

Magnetic field intensities.

• 17.
Compared to the primary voltage, the secondary voltage may be
• A.

Larger.

• B.

Smaller.

• C.

The same.

• D.

The same or smaller, but not larger.

• E.

Larger, smaller, or the same.

• 18.
The output power of an ideal transformer is
• A.

Greater than the input power.

• B.

Equal to the input power.

• C.

Smaller than the input power.

• D.

May be any of these

• 19.
Disconnect a small-voltage battery from a coil of many loops of wire and a large voltage is produced by
• A.

The sudden collapse in the magnetic field.

• B.

Latent energy in the battery.

• C.

The resistance of the battery to a change in polarity.

• D.

Electrons already in the wire.

• E.

The electric field between the battery terminals.

• 20.
Power is transmitted at high voltages because the corresponding current in the wires is
• A.

Also high to deliver appreciable power to distant places.

• B.

Low so that overheating of the wires is minimized.

• C.

Choices A and B are both true.

• D.

Choices A and B are both false.

• 21.
Rapid change of a magnetic field induces
• A.

A magnetic field of greater magnitude.

• B.

A magnetic field of the same magnitude.

• C.

An electric field.

• 22.
The metal detectors that people walk through at airports operate via
• A.

Ohm's law.

• B.

• C.

Coulomb's law.

• D.

Newton's laws.

• E.

Civil laws.

• 23.
A step-up transformer increases
• A.

Power.

• B.

Energy.

• C.

Both power and energy.

• D.

Neither power or energy.

• 24.
A step-up transformer has a ratio of one to ten. Neglecting slight losses, if 100 W of power go into the primary coil, the power coming from the secondary coil is
• A.

1 W.

• B.

10 W.

• C.

100 W.

• D.

1000 W.

• E.

None of these

• 25.
A certain transformer doubles input voltage. If the primary coil has 10 A of current, then the current in the secondary coil is
• A.

2 A.

• B.

5 A.

• C.

10 A.

• D.

25 A.

• E.

None of these

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