Chapter 25: electromagnetic induction

D

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.

C

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.

B

3) When a magnet is thrust into a coil of 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.

B

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.

D

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) all of these.

E) none of these.

E

6) A wire moving sidewise in a magnetic field has NO induced voltage if

A) it is moving in the direction of the field..

B) it is moving opposite the direction of the field.

C) it is made of copper.

D) it is moving very fast.

E) two of these.

D

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.

C

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.

A

9) An electric motor and electric generator are

A) very similar devices. B) entirely different devices.

B

10) A device that transforms electrical energy to mechanical energy is a

A) generator.

B) motor.

C) transformer.

D) magnet.

E) none of these.

A

11) A device that transforms mechanical energy into electrical energy is a

A) generator.

B) motor.

C) transformer.

D) magnet.

E) none of these.

B

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.

C

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) both of these.

D) neither of these.

A

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 these.

C

15) The primary of a transformer is the coil connected to

A) the load. B) the Internet. C) the power line. D) none of these.

C

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.

E

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.

B

18) The output power of a 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.

A

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

A) the large 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.

B

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) both of these.

D) neither of these.

A

21) Electric power can be transmitted from one place to another without the need for connecting wires in between. This statement is

A) true. B) false.

C

22) 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.

B

23) The metal detectors that people walk through at airports operate via

A) Ohm's law.

B) Faraday's law.

C) Coulomb's law.

D) Newton's laws.

E) civil laws.

D

24) A step-up transformer increases

A) power. B) energy.

C) both of these. D) neither of these.

C

25) 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.

B

26) 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.

C

27) Metal detectors, like the ones used at airports, are activated by

A) electric fields. B) magnetic fields.

C) electromagnetic induction. D) alternating current.

C

28) The principal advantage of ac power over dc power is that

A) less energy is dissipated during transmission.

B) ac voltage oscillates while dc voltage does not.

C) ac voltage can be transformed via conventional transformers.

D) ac circuits multiply power more easily.

E) ac circuits are safer.

E

29) The major advantage of MHD generators over conventional generators is that MHD generators

A) do not use electromagnetic induction.

B) do not require magnets.

C) require no power input.

D) all of these.

E) none of these.

A

30) Neon signs require about 12,000 volts to operate. If the circuit uses a 120-volt power source, the ratio of primary to secondary turns on the transformer should be

A) 1:100. B) 100:1. C) neither of these.

B

31) The voltage across the input terminals of a transformer is 110 V. The primary has 50 loops and the secondary has 25 loops. The voltage the transformer puts out is

A) 25 V.

B) 55 V.

C) 110 V.

D) 220 V.

E) none of these.

C

32) Four amperes of current exist in the primary coil of a transformer. The voltage across the primary coil is 110 V. What is the power output of the secondary coil?

A) 27.5 W

B) 110 W

C) 440 W

D) 880 W

E) not enough information to say

C

33) Disregarding the effects of friction, a cyclist will coast farther when a lamp powered by a wheel generator is

A) of low wattage. B) of high wattage.

C) burned out. D) none of these.

B

34) As a motor armature turns faster and faster, net current in the motor windings

A) increases. B) decreases. C) remains unchanged.

D

35) If the primary of a transformer were connected to a dc power source, the transformer would have a voltage output

A) at a higher efficiency than with an ac source.

B) the same.

C) that is also dc.

D) only while being connected or disconnected.

E) none of these.