Electromagnetic Induction

1
Chapter 25

• Electromagnetic Induction

2
Voltage will be induced in a wire loop when a
magnetic field within that loop

1. changes.
2. aligns with the electric field.
3. is at right angles to the electric field.
4. converts to magnetic energy.

3
Voltage will be induced in a wire loop when a
magnetic field within that loop

1. changes.
2. aligns with the electric field.
3. is at right angles to the electric field.
4. converts to magnetic energy.

4
When you thrust a bar magnet to and fro into a
coil of wire, you induce

1. direct current.
2. alternating current.
3. neither dc nor ac.
4. alternating voltage only, not current.

5
When you thrust a bar magnet to and fro into a
coil of wire, you induce

1. direct current.
2. alternating current.
3. neither dc nor ac.
4. alternating voltage only, not current.

Explanation Indeed alternating voltage is
induced, which produces alternating current, so
we can say that current as well as voltage is
induced in a metal coil. Hence b is correct.
6
When a magnet is moved into a wire coil, an
induced current in the coil produces a magnetic
field that

1. resists motion of the magnet.
2. attracts the magnet.
3. has negligible effect on the magnet.
4. interferes with the electric field.

7
When a magnet is moved into a wire coil, an
induced current in the coil produces a magnetic
field that

1. resists motion of the magnet.
2. attracts the magnet.
3. has negligible effect on the magnet.
4. interferes with the electric field.

Comment This is shown in Figure 25.4.
8
Faradays law is the law

1. of energy conservation.
2. of charge conservation.
3. of electromagnetic induction.
4. that connects voltage and resistance to magnetic
   fields.

9
Faradays law is the law

1. of energy conservation.
2. of charge conservation.
3. of electromagnetic induction.
4. that connects voltage and resistance to magnetic
   fields.

Comment Answer a has merit, but answer c is
central. Answer d is gibberish.
10
The underlying physics of an electric motor is
that

1. electric and magnetic fields repel each other.
2. a current-carrying wire experiences force in a
   magnetic field.
3. like magnetic poles repel each other.
4. ac voltage is induced by a changing magnetic
   field.

11
The underlying physics of an electric motor is
that

1. electric and magnetic fields repel each other.
2. a current-carrying wire experiences force in a
   magnetic field.
3. like magnetic poles repel each other.
4. ac voltage is induced by a changing magnetic
   field.

Comment Answer c is indirect, but answer b is
more direct.
12
The essential physics concept in an electric
generator is

1. Coulombs law.
2. Ohms law.
3. Faradays law.
4. Newtons second law.

13
The essential physics concept in an electric
generator is

1. Coulombs law.
2. Ohms law.
3. Faradays law.
4. Newtons second law.

14
Within both a conventional ammeter and voltmeter
you will find a

1. diode.
2. capacitor.
3. galvanometer.
4. tiny motor.

15
Within both a conventional ammeter and voltmeter
you will find a

1. diode.
2. capacitor.
3. galvanometer.
4. tiny motor.

16
Both a motor and a generator operate via

1. similar concepts.
2. quite different concepts.
3. idealized transformers.
4. independent energy sources.

17
Both a motor and a generator operate via

1. similar concepts.
2. quite different concepts.
3. idealized transformers.
4. independent energy sources.

18
The major difference between a motor and
generator is

1. input and output.
2. direction of windings of coils.
3. that one uses ac, and the other dc.
4. primarily cosmetic.

19
The major difference between a motor and
generator is

1. input and output.
2. direction of windings of coils.
3. that one uses ac, and the other dc.
4. primarily cosmetic.

Explanation The main difference between a motor
and a generator is the roles of input and output,
which is opposite for each.
20
When a generator is used to light a lamp, the
energy of the lit lamp originates in the

1. coils of wire in the generator.
2. magnet inside the generator.
3. lamp itself.
4. work done to turn the coils in the generator.

21
When a generator is used to light a lamp, the
energy of the lit lamp originates in the

1. coils of wire in the generator.
2. magnet inside the generator.
3. lamp itself.
4. work done to turn the coils in the generator.

22
The purpose of a transformer is to transform

1. and create energy.
2. power at one voltage to the same power at another
   voltage.
3. current from one place to another.
4. voltage to useful applications.

23
The purpose of a transformer is to transform

1. and create energy.
2. power at one voltage to the same power at another
   voltage.
3. current from one place to another.
4. voltage to useful applications.

Explanation Answers c or d are not the best
choices, as is b, the more direct answer. If you
answered a, OUCH! no device creates energy!
24
A transformer works by way of

1. Coulombs law.
2. Ohms law.
3. Faradays law.
4. Newtons second law.

25
A transformer works by way of

1. Coulombs law.
2. Ohms law.
3. Faradays law.
4. Newtons second law.

26
A step-up transformer in an electrical circuit
can step up

1. voltage.
2. energy.
3. Both of these.
4. None of these.

27
A step-up transformer in an electrical circuit
can step up

1. voltage.
2. energy.
3. Both of these.
4. None of these.

Explanation Stepping up energy is a big no-no in
energy conservation!
28
A step-down transformer has a greater number of
coils on the

1. input side.
2. output side.
3. side with lower power.
4. None of the above.

29
A step-down transformer has a greater number of
coils on the

1. input side.
2. output side.
3. side with lower power.
4. None of the above.

Comment The fewer number of coils on the output
side steps voltage down.
30
The workings of a transformer are consistent
mainly with

1. Newtons second law.
2. Coulombs law.
3. the conservation of momentum.
4. the conservation of energy.

31
The workings of a transformer are consistent
mainly with

1. Newtons second law.
2. Coulombs law.
3. the conservation of momentum.
4. the conservation of energy.

32
To minimize heat losses for power transported
across the countryside, it is best that current
in the wires is

1. low.
2. high.
3. not too low and not too high.
4. replaced with voltage.

33
To minimize heat losses for power transported
across the countryside, it is best that current
in the wires is

1. low.
2. high.
3. not too low and not too high.
4. replaced with voltage.

Comment High amperage produces large heat
losses. So power at low current (and
correspondingly high voltage) means less heat
loss.
34
Lighting a lamp via electromagnetic induction

1. bypasses the need of work input.
2. requires work input.
3. may or may not require work input depending on
   efficiency.
4. produces a low-heat lamp.

35
Lighting a lamp via electromagnetic induction

1. bypasses the need of work input.
2. requires work input.
3. may or may not require work input depending on
   efficiency.
4. produces a low-heat lamp.

Comment Never forget an important fundamental of
physics Work is necessary to transform energy,
whether the means of doing so is electromagnetic
induction or otherwise.
36
A changing electric field can induce a changing

1. current loop.
2. voltage.
3. resonance that produces radio.
4. magnetic field.

37
A changing electric field can induce a changing

1. current loop.
2. voltage.
3. resonance that produces radio.
4. magnetic field.

Comment This was Maxwells generalization of
electromagnetic induction.
38
If you change the magnetic field in a closed loop
of wire, you induce in the loop a

1. current.  
2. voltage.  
3. electric field.  
4. All of these.  

39
If you change the magnetic field in a closed loop
of wire, you induce in the loop a

1. current.  
2. voltage.  
3. electric field.  
4. All of these.  

Explanation Recall how Maxwell generalized
Faradays law to include induction of an electric
field.
40
The fact that electric and magnetic fields
regenerate each other is important in

1. burglar alarms.
2. radio broadcasting.
3. metal detectors.
4. All of these. 

41
The fact that electric and magnetic fields
regenerate each other is important in

1. burglar alarms.
2. radio broadcasting.
3. metal detectors.
4. All of these. 

Explanation A general answer would be
electromagnetic waves, of which only radio
broadcasting qualifies.