Download Physics Ch 20 pp notes

How to Use This Presentation
• To View the presentation as a slideshow with effects
select “View” on the menu bar and click on “Slide Show.”
• To advance through the presentation, click the right-arrow
key or the space bar.
• From the resources slide, click on any resource to see a
presentation for that resource.
• From the Chapter menu screen click on any lesson to go
directly to that lesson’s presentation.
• You may exit the slide show at any time by pressing
the Esc key.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Resources
Chapter Presentation
Transparencies
Visual Concepts
Sample Problems
Standardized Test Prep
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Electromagnetic Induction
Table of Contents
Section 1 Electricity from Magnetism
Section 2 Generators, Motors, and Mutual Inductance
Section 3 AC Circuits and Transformers
Section 4 Electromagnetic Waves
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Objectives
• Recognize that relative motion between a conductor
and a magnetic field induces an emf in the conductor.
• Describe how the change in the number of magnetic
field lines through a circuit loop affects the magnitude
and direction of the induced electric current.
• Apply Lenz’s law and Faraday’s law of induction to
solve problems involving induced emf and current.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Electromagnetic Induction
• Electromagnetic induction is the process of
creating a current in a circuit by a changing magnetic
field.
• A change in the magnetic flux through a conductor
induces an electric current in the conductor.
• The separation of charges by the magnetic force
induces an emf.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Electromagnetic Induction in a Circuit Loop
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Electromagnetic Induction, continued
• The angle between a magnetic field and a circuit
affects induction.
• A change in the number of magnetic field lines
induces a current.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Ways of Inducing a Current in a Circuit
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Characteristics of Induced Current
• Lenz’s Law
The magnetic field of the induced current is in a
direction to produce a field that opposes the
change causing it.
• Note: the induced current does not oppose the
applied field, but rather the change in the applied
field.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Lenz's Law for Determining the Direction of
the Induced Current
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Characteristics of Induced Current, continued
• The magnitude of the induced emf can be predicted
by Faraday’s law of magnetic induction.
• Faraday’s Law of Magnetic Induction
 M
emf  – N
t
average induced emf = –the number of loops in the circuit 
the time rate of change in the magnetic flux
•
The magnetic flux is given by M = ABcosq.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Sample Problem
Induced emf and Current
A coil with 25 turns of wire is wrapped around a
hollow tube with an area of 1.8 m2. Each turn has
the same area as the tube. A uniform magnetic field
is applied at a right angle to the plane of the coil. If
the field increases uniformly from 0.00 T to 0.55 T in
0.85 s, find the magnitude of the induced emf in the
coil. If the resistance in the coil is 2.5 Ω, find the
magnitude of the induced current in the coil.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Sample Problem, continued
Induced emf and Current
1. Define
Given:
∆t = 0.85 s
A = 1.8 m2
N = 25 turns
R = 2.5 Ω
Bi = 0.00 T = 0.00 V•s/m2
Bf = 0.55 T = 0.55 V•s/m2
Unknown:
emf = ?
I=?
q = 0.0º
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Sample Problem, continued
Induced emf and Current
1. Define, continued
Diagram: Show the coil before and after the change
in the magnetic field.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Sample Problem, continued
Induced emf and Current
2. Plan
Choose an equation or situation. Use Faraday’s
law of magnetic induction to find the induced emf in
the coil.
  AB cosq 
 M
emf  – N
 –N
t
t
Substitute the induced emf into the definition of
resistance to determine the induced current in the
coil.
emf
I
R
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Sample Problem, continued
Induced emf and Current
2. Plan, continued
Rearrange the equation to isolate the unknown.
In this example, only the magnetic field strength
changes with time. The other components (the coil
area and the angle between the magnetic field and
the coil) remain constant.
B
emf  – NA cos q
t
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Sample Problem, continued
Induced emf and Current
3. Calculate
Substitute the values into the equation and
solve.

V•s  
0.55
–
0.00
2 

m


emf  –(25)(1.8 m2 )(cos0.0º ) 
 –29 V
(0.85 s)
–29 V
I
 –12 A
2.5 Ω
emf  –29 V
I  –12 A
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Sample Problem, continued
Induced emf and Current
4. Evaluate
The induced emf, and therefore the induced
current, is directed through the coil so that the
magnetic field produced by the induced current
opposes the change in the applied magnetic
field. For the diagram shown on the previous
page, the induced magnetic field is directed to
the right and the current that produces it is
directed from left to right through the resistor.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
Objectives
• Describe how generators and motors operate.
• Explain the energy conversions that take place in
generators and motors.
• Describe how mutual induction occurs in circuits.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
Generators and Alternating Current
• A generator is a machine that converts mechanical
energy into electrical energy.
• Generators use induction to convert mechanical
energy into electrical energy.
• A generator produces a continuously changing emf.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
Induction of an emf in an AC Generator
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
Function of a Generator
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
Generators and Alternating Current, continued
• Alternating current is an electric current that
changes direction at regular intervals.
• Alternating current can be converted to direct
current by using a device called a commutator to
change the direction of the current.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
Comparing AC and DC Generators
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
Motors
• Motors are machines that convert electrical energy
to mechanical energy.
• Motors use an arrangement similar to that of
generators.
• Back emf is the emf induced in a motor’s coil that
tends to reduce the current in the coil of a motor.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
DC Motors
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
Mutual Inductance
• The ability of one circuit to induce an emf in a nearby
circuit in the presence of a changing current is called
mutual inductance.
• In terms of changing primary current, Faraday’s law
is given by the following equation, where M is the
mutual inductance:
M
I
emf  –N
 –M
t
t
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 2 Generators, Motors,
and Mutual Inductance
Mutual Inductance
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Objectives
• Distinguish between rms values and maximum
values of current and potential difference.
• Solve problems involving rms and maximum values
of current and emf for ac circuits.
• Apply the transformer equation to solve problems
involving step-up and step-down transformers.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Effective Current
• The root-mean-square (rms) current of a circuit is
the value of alternating current that gives the same
heating effect that the corresponding value of direct
current does.
• rms Current
Irms 
Imax
2
 0.707 Imax
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Effective Current, continued
• The rms current and rms emf in an ac circuit are
important measures of the characteristics of an ac
circuit.
• Resistance influences current in an ac circuit.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
rms Current
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Sample Problem
rms Current and emf
A generator with a maximum output emf of 205 V is
connected to a 115 Ω resistor. Calculate the rms
potential difference. Find the rms current through the
resistor. Find the maximum ac current in the circuit.
1. Define
Given:
∆Vrms = 205 V R = 115 Ω
Unknown:
∆Vrms = ? Irms = ? Imax = ?
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Sample Problem, continued
rms Current and emf
2. Plan
Choose an equation or situation. Use the equation
for the rms potential difference to find ∆Vrms.
∆Vrms = 0.707 ∆Vmax
Rearrange the definition for resistance to calculate
Irms.
Vrms
Irms 
R
Use the equation for rms current to find Irms.
Irms = 0.707 Imax
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Sample Problem, continued
rms Current and emf
2. Plan, continued
Rearrange the equation to isolate the unknown.
Rearrange the equation relating rms current to
maximum current so that maximum current is
calculated.
Irms
Imax 
0.707
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Sample Problem, continued
rms Current and emf
3. Calculate
Substitute the values into the equation and solve.
Vrms  (0.707)(205 V)  145 V
145 V
Irms 
 1.26 A
115 Ω
1.26 A
Imax 
 1.78 A
0.707
4. Evaluate The rms values for emf and current
are a little more than two-thirds the maximum
values, as expected.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Transformers
• A transformer is a device that increases or
decreases the emf of alternating current.
• The relationship between the input and output emf is
given by the transformer equation.
N
V2  2 V1
N1
induced emf in secondary =
 number of turns in secondary 
 number of turns in primary  applied emf in primary


Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Transformers
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
Transformers, continued
• The transformer equation assumes that no power is
lost between the primary and secondary coils.
However, real transformers are not perfectly efficient.
• Real transformers typically have efficiencies ranging
from 90% to 99%.
• The ignition coil in a gasoline engine is a transformer.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 3 AC Circuits and
Transformers
A Step-Up Transformer in an Auto Ignition System
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 4 Electromagnetic
Waves
Objectives
• Describe what electromagnetic waves are and how
they are produced.
• Recognize that electricity and magnetism are two
aspects of a single electromagnetic force.
• Explain how electromagnetic waves transfer energy.
• Describe various applications of electromagnetic
waves.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 4 Electromagnetic
Waves
Propagation of Electromagnetic Waves
• Electromagnetic waves travel at the speed of light
and are associated with oscillating, perpendicular
electric and magnetic fields.
• Electromagnetic waves are transverse waves; that is,
the direction of travel is perpendicular to the the
direction of oscillating electric and magnetic fields.
• Electric and magnetic forces are aspects of a single
force called the electromagnetic force.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 4 Electromagnetic
Waves
Electromagnetic Waves
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 4 Electromagnetic
Waves
Propagation of Electromagnetic Waves,
continued
• All electromagnetic waves are produced by
accelerating charges.
• Electromagnetic waves transfer energy. The energy
of electromagnetic waves is stored in the waves’
oscillating electric and magnetic fields.
• Electromagnetic radiation is the transfer of energy
associated with an electric and magnetic field.
Electromagnetic radiation varies periodically and
travels at the speed of light.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 4 Electromagnetic
Waves
The Sun at Different Wavelengths of Radiation
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 4 Electromagnetic
Waves
Propagation of Electromagnetic Waves,
continued
• High-energy electromagnetic waves behave like
particles.
• An electromagnetic wave’s frequency makes the
wave behave more like a particle. This notion is
called the wave-particle duality.
• A photon is a unit or quantum of light. Photons can
be thought of as particles of electromagnetic radiation
that have zero mass and carry one quantum of
energy.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 4 Electromagnetic
Waves
The Electromagnetic Spectrum
• The electromagnetic spectrum ranges from very long
radio waves to very short-wavelength gamma waves.
• The electromagnetic spectrum has a wide variety of
applications and characteristics that cover a broad
range of wavelengths and frequencies.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 4 Electromagnetic
Waves
The Electromagnetic Spectrum, continued
• Radio Waves
– longest wavelengths
– communications, tv
• Microwaves
– 30 cm to 1 mm
– radar, cell phones
• Infrared
– 1 mm to 700 nm
– heat, photography
• Visible light
– 700 nm (red) to 400 nm
(violet)
• Ultraviolet
– 400 nm to 60 nm
– disinfection,
spectroscopy
• X rays
– 60 nm to 10–4 nm
– medicine, astronomy,
security screening
• Gamma Rays
– less than 0.1 nm
– cancer treatment,
astronomy
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 4 Electromagnetic
Waves
The Electromagnetic Spectrum
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice
1. Which of the following equations correctly describes
Faraday’s law of induction?
A. emf
B. emf
C. emf
D. emf
( AB tanq )
 –N
t
( AB cos q )
N
t
( AB cos q )
 –N
t
( AB cos q )
M
t
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
1. Which of the following equations correctly describes
Faraday’s law of induction?
A. emf
B. emf
C. emf
D. emf
( AB tanq )
 –N
t
( AB cos q )
N
t
( AB cos q )
 –N
t
( AB cos q )
M
t
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
2. For the coil shown at right, what must be
done to induce a clockwise current?
F. Either move the north pole of a magnet
down into the coil, or move the south pole
of the magnet up and out of the coil.
G. Either move the south pole of a magnet
down into the coil, or move the north pole of
the magnet up and out of the coil.
H. Move either pole of the magnet down
into the coil.
J. Move either pole of the magnet up and
out of the coil.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
2. For the coil shown at right, what must be
done to induce a clockwise current?
F. Either move the north pole of a magnet
down into the coil, or move the south pole
of the magnet up and out of the coil.
G. Either move the south pole of a magnet
down into the coil, or move the north pole of
the magnet up and out of the coil.
H. Move either pole of the magnet down
into the coil.
J. Move either pole of the magnet up and
out of the coil.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
3. Which of the following would not increase the emf
produced by a generator?
A. rotating the generator coil faster
B. increasing the strength of the generator magnets
C. increasing the number of turns of wire in the coil
D. reducing the cross-sectional area of the coil
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
3. Which of the following would not increase the emf
produced by a generator?
A. rotating the generator coil faster
B. increasing the strength of the generator magnets
C. increasing the number of turns of wire in the coil
D. reducing the cross-sectional area of the coil
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
4. By what factor do you multiply the maximum emf to
calculate the rms emf for an alternating current?
F. 2
G.
H.
2
1
2
1
J.
2
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
4. By what factor do you multiply the maximum emf to
calculate the rms emf for an alternating current?
F. 2
G.
H.
2
1
2
1
J.
2
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
5. Which of the following correctly describes the composition
of an electromagnetic wave?
A. a transverse electric wave and a magnetic transverse
wave that are parallel and are moving in the same
direction
B. a transverse electric wave and a magnetic transverse
wave that are perpendicular and are moving in the same
direction
C. a transverse electric wave and a magnetic transverse
wave that are parallel and are moving at right angles to
each other
D. a transverse electric wave and a magnetic transverse
wave that are perpendicular and are moving at right
angles to each other
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
5. Which of the following correctly describes the composition
of an electromagnetic wave?
A. a transverse electric wave and a magnetic transverse
wave that are parallel and are moving in the same
direction
B. a transverse electric wave and a magnetic transverse
wave that are perpendicular and are moving in the same
direction
C. a transverse electric wave and a magnetic transverse
wave that are parallel and are moving at right angles to
each other
D. a transverse electric wave and a magnetic transverse
wave that are perpendicular and are moving at right
angles to each other
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
6. A coil is moved out of a magnetic field in order to induce
an emf. The wire of the coil is then rewound so that the
area of the coil is increased by 1.5 times. Extra wire is
used in the coil so that the number of turns is doubled. If
the time in which the coil is removed from the field is
reduced by half and the magnetic field strength remains
unchanged, how many times greater is the new induced
emf than the original induced emf ?
F. 1.5 times
G. 2 times
H. 3 times
J. 6 times
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
6. A coil is moved out of a magnetic field in order to induce
an emf. The wire of the coil is then rewound so that the
area of the coil is increased by 1.5 times. Extra wire is
used in the coil so that the number of turns is doubled. If
the time in which the coil is removed from the field is
reduced by half and the magnetic field strength remains
unchanged, how many times greater is the new induced
emf than the original induced emf ?
F. 1.5 times
G. 2 times
H. 3 times
J. 6 times
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
Use the passage below to
answer questions 7–8.
A pair of transformers is
connected in series, as
shown in the figure below.
7. From left to right, what are
the types of the two
transformers?
A. Both are step-down
transformers.
B. Both are step-up
transformers.
C. One is a step-down
transformer; and one is a
step-up transformer.
D. One is a step-up
transformer; and one is a
step-down transformer.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
Use the passage below to
answer questions 7–8.
A pair of transformers is
connected in series, as
shown in the figure below.
7. From left to right, what are
the types of the two
transformers?
A. Both are step-down
transformers.
B. Both are step-up
transformers.
C. One is a step-down
transformer; and one is a
step-up transformer.
D. One is a step-up
transformer; and one is a
step-down transformer.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
Use the passage below to
answer questions 7–8.
A pair of transformers is
connected in series, as
shown in the figure below.
8. What is the output
potential difference from
the secondary coil of
the transformer on the
right?
F. 400 V
G. 12 000 V
H. 160 000 V
J. 360 000 V
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
Use the passage below to
answer questions 7–8.
A pair of transformers is
connected in series, as
shown in the figure below.
8. What is the output
potential difference from
the secondary coil of
the transformer on the
right?
F. 400 V
G. 12 000 V
H. 160 000 V
J. 360 000 V
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
9. What are the particles that can be used to describe
electromagnetic radiation called?
A. electrons
B. magnetons
C. photons
D. protons
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
9. What are the particles that can be used to describe
electromagnetic radiation called?
A. electrons
B. magnetons
C. photons
D. protons
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
10. The maximum values for the current and potential
difference in an ac circuit are 3.5 A and 340 V,
respectively. How much power is dissipated in this
circuit?
F. 300 W
G. 600 W
H. 1200 W
J. 2400 W
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Multiple Choice, continued
10. The maximum values for the current and potential
difference in an ac circuit are 3.5 A and 340 V,
respectively. How much power is dissipated in this
circuit?
F. 300 W
G. 600 W
H. 1200 W
J. 2400 W
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Short Response
11. The alternating current through an electric toaster
has a maximum value of 12.0 A. What is the rms
value of this current?
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Short Response, continued
11. The alternating current through an electric toaster
has a maximum value of 12.0 A. What is the rms
value of this current?
Answer:
8.48 A
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Short Response, continued
12. What is the purpose of a commutator in an ac
generator?
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Short Response, continued
12. What is the purpose of a commutator in an ac
generator?
Answer:
It converts ac to a changing current in one
direction only.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Short Response, continued
13. How does the energy of one photon of an
electromagnetic wave relate to the wave’s
frequency?
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Short Response, continued
13. How does the energy of one photon of an
electromagnetic wave relate to the wave’s
frequency?
Answer:
The energy is directly proportional to the wave’s
frequency (E = hf ).
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Short Response, continued
14. A transformer has 150 turns of wire on the primary
coil and 75 000 turns on the secondary coil. If the
input potential difference across the primary is 120 V,
what is the output potential difference across the
secondary?
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Short Response, continued
14. A transformer has 150 turns of wire on the primary
coil and 75 000 turns on the secondary coil. If the
input potential difference across the primary is 120 V,
what is the output potential difference across the
secondary?
Answer:
6.0  104 V
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Extended Response
15. Why is alternating current used for power
transmission instead of direct current? Be sure to
include power dissipation and electrical safety
considerations in your answer.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Extended Response, continued
15. Answer:
For electric power to be transferred over long
distances without a large amount of power
dissipation, the electric power must have a high
potential difference and low current. However, to
be safely used in homes, the potential difference
must be lower than that used for long-distance
power transmission. Because of induction, the
potential difference and current of electricity can
be transformed to higher or lower values, but the
current must change continuously (alternate) for
this to happen.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Extended Response, continued
Base your answers to questions
16. Why must the current enter
16–18 on the information below.
the coil just as someone
comes up to the table?
A device at a carnival’s haunted
house involves a metal ring that
flies upward from a table when a
patron passes near the table’s
edge. The device consists of a
photoelectric switch that activates
the circuit when anyone walks in
front of the switch and of a coil of
wire into which a current is
suddenly introduced when the
switch is triggered.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Extended Response, continued
Base your answers to questions
16. Why must the current enter
16–18 on the information below.
the coil just as someone
comes up to the table?
A device at a carnival’s haunted
house involves a metal ring that
flies upward from a table when a Answer: The change in current
in the coil will produce a
patron passes near the table’s
changing magnetic field,
edge. The device consists of a
which will induce a current in
photoelectric switch that activates
the ring. The induced current
the circuit when anyone walks in
produces a magnetic field
front of the switch and of a coil of
that interacts with the
wire into which a current is
magnetic field from the coil,
suddenly introduced when the
causing the ring to rise from
switch is triggered.
the table.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Extended Response, continued
Base your answers to questions
17. Using Lenz’s law, explain
16–18 on the information below.
why the ring flies upward
when there is an increasing
A device at a carnival’s haunted
current in the coil?
house involves a metal ring that
flies upward from a table when a
patron passes near the table’s
edge. The device consists of a
photoelectric switch that activates
the circuit when anyone walks in
front of the switch and of a coil of
wire into which a current is
suddenly introduced when the
switch is triggered.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Extended Response, continued
Base your answers to questions
17. Using Lenz’s law, explain
16–18 on the information below.
why the ring flies upward
when there is an increasing
A device at a carnival’s haunted
current in the coil?
house involves a metal ring that
flies upward from a table when a
Answer: According to Lenz’s
patron passes near the table’s
law, the magnetic field
edge. The device consists of a
induced in the ring must
photoelectric switch that activates
oppose the magnetic field
the circuit when anyone walks in
that induces the current in
front of the switch and of a coil of
the ring. The opposing fields
wire into which a current is
cause the ring, which can
suddenly introduced when the
move freely, to rise upward
switch is triggered.
from the coil under the
table’s surface.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Extended Response, continued
Base your answers to questions
18. Suppose the change
16–18 on the information below.
in the magnetic field is
A device at a carnival’s haunted
0.10 T/s. If the radius of
house involves a metal ring that
the ring is 2.4 cm and
flies upward from a table when a
the ring is assumed to
patron passes near the table’s
consist of one turn of
edge. The device consists of a
wire, what is the emf
photoelectric switch that activates
induced in the ring?
the circuit when anyone walks in
front of the switch and of a coil of
wire into which a current is
suddenly introduced when the
switch is triggered.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Extended Response, continued
Base your answers to questions
18. Suppose the change
16–18 on the information below.
in the magnetic field is
A device at a carnival’s haunted
0.10 T/s. If the radius of
house involves a metal ring that
the ring is 2.4 cm and
flies upward from a table when a
the ring is assumed to
patron passes near the table’s
consist of one turn of
edge. The device consists of a
wire, what is the emf
photoelectric switch that activates
induced in the ring?
the circuit when anyone walks in
front of the switch and of a coil of
wire into which a current is
Answer: 1.8  10–4 V
suddenly introduced when the
switch is triggered.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Section 1 Electricity from
Magnetism
Ways of Inducing a Current in a Circuit
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.