Transcript R - BYU Physics and Astronomy

Class 2
Today we will:
• learn the basic characteristics of the electrostatic force
• review the properties of conductors and insulators
• learn what is meant by “electrostatic induction”
• find out why static electrostatic forces are usually attractive
• discuss the problem of force at a distance
• learn the basics of two types of models that explain
why there are forces
Clicker Question 1
When babies are rubbed, they gain a net charge.
Does the ceiling need a net charge for the babies
to stick to it?
A. yes
B. no
Clicker Question 2
If the ceiling has no net charge, is it possible for the
babies to be repelled by the ceiling?
A. yes
B. no
Clicker Question 3
If the virtual particles were uncharged real particles,
the force would be
A. always attractive.
B. always repulsive.
C. either attractive or repulsive.
D. There would be no force.
Answers
1B
2B
3B
Class 3
Today we will:
• learn how the thread model describes the force between
point charges at rest
• construct Coulomb’s law from the thread model
• learn how to use Coulomb’s law to calculate the force
between charges at rest
Clicker Question 1
source charge
field charge
Force
The field particle is
A. positive
B. negative
C. neutral
D. You can’t tell.
Clicker Question 2
 qs q f r
F
40 r 3
+3C
(2, 3)
−4C
(7, 1)
If we wish to find the force on the blue particle,
A. the blue particle is the source particle.
B. the blue particle is the field particle.
C. both particles are source particles.
D. both particles are field particles.
E. none of the above.
Clicker Question 3
 qs q f r
F
40 r 3
+3C
(2, 3)
−4C
(7, 1)

The vector r goes from the source particle to

the field particle.
A. r  7 xˆ  1 yˆ

B. r  2 xˆ  3 yˆ

C. r  5 xˆ  2 yˆ

D. r  5 xˆ  2 yˆ

E. r  5.39
Answers
1A
2B
3D
Class 4
Today we will:
• review the meaning of potential energy
• find the potential energy of point charges at rest
• learn a few basic ideas about relativity
• find out how relativity affects the threads emitted
by a moving source
Clicker Question 1
In a region of space, the force on a positive test
charge is zero. In this region, the potential energy is
A. positive.
B. negative.
C. zero.
D. a constant, but not necessarily zero.

F 0
Clicker Question 2
v

c
The SI units for β are:
A. m/s2
B. m2/s
C. m2/s2
D. β is dimensionless
Clicker Question 3
rest
moving
H
0
L
H'

L'
A. L  L and    0
B. H   H and    0
C. L  L and    0
D. H   H and    0
E. L  L and    0
Answers
1D
2D
3E
Class 5
Today we will:
• learn the meaning of head lines, tail lines, and
ray lines.
• find a force equation for a moving source
charge (like Coulomb’s law, but for a source with
constant velocity).
• learn how stubs can be used to make a
account for the motion of field particles.
Clicker Question 1
P
B
D
E - out of screen
C
S
A
U
A source charge and a field charge are both
positive. The source at S emits threads that arrive
at P when the source has moved to U.
What is the direction of the thread?
Clicker Question 2
P
B
D
E - out of screen
C
S
A
U
A source charge and a field charge are both
positive. The source at S emits threads that arrive
at P when the source has moved to U.
What is the direction of the thread (electric) force?
Clicker Question 3
P
B
D
E - out of screen
C
S
A
U
A source charge and a field charge are both
positive. The source at S emits threads that arrive
at P when the source has moved to U.
What is the direction of the head line?
Clicker Question 4
P
B
D
E - out of screen
C
S
A
U
A source charge and a field charge are both
positive. The source at S emits threads that arrive
at P when the source has moved to U.
What is the direction of the stub?
Clicker Question 5
B
A
P

v
E - out of screen
C
D
S
U
A source charge and a field charge are both
positive. The source at S emits threads that arrive
at P when the source has moved to U.
What is the direction of the stub (magnetic) force?
Answers
1B
2B
3D
4E
5D
Class 6
Today we will:
• learn that threads and stubs can be aligned to
form electric and magnetic field lines.
• derive the Lorentz force law.
• integrate to find the electric and magnetic fields
of a proton beam.
Clicker Question 1
P
B
D
E - out of screen
C
S
A
U
A source charge and a field charge are both
positive. The source at S emits threads that arrive
at P when the source has moved to U.
What is the direction of the stubs?
Clicker Question 2
A proton travels vertically downward through a
region where there is an electric field pointing
to the east.
What is the direction of the force?
A. downward
B. to the east
C. to the south
D. to the north
E. to the west
Clicker Question 3
A proton travels vertically downward through a
region where there is a magnetic field pointing
to the east.
What is the direction of the force?
A. downward
B. to the east
C. to the south
D. to the north
E. to the west
Clicker Question 4
An electron travels vertically downward through a
region where there is a magnetic field pointing
to the east.
What is the direction of the force?
A. downward
B. to the east
C. to the south
D. to the north
E. to the west
Answers
1E
2B
3C
4D
Class 7
Today we will:
• learn how to do problems using the Lorentz force
law.
• learn the meaning of the electric potential and
how it relates to the potential energy.
• learn three ways of representing fields
geometrically.
Clicker Question 1

v  5.00 m/s xˆ.

B  3.50 mT xˆ  2.00 mT yˆ.
If we change the magnetic field to

B  7.00 mT xˆ  2.00 mT yˆ.
what happens to the force?
Before:
A.
B.
C.
D.
E.
It doubles.
Its get smaller by a factor of 2.
Its z-component doubles.
Its z-component gets smaller by factor of 2.
Nothing changes.
Clicker Question 2
An electron passes through a 1.0 V battery. The
electron charge is e  1.602 1019 C.
By how much does the energy of the electron
increase?
A. U  1.602 10 19 J.
B. U  3.204 10
19
J.
C. U  0.80110 19 J.
D. U  0 J.
Clicker Question 2
An electron passes through a 1.0 V battery. The
electron charge is e  1.602 1019 C.
Batteries increase the potential energy of electrons
by pushing them closer together.
Clicker Question 3
Two identical spheres have charges +q. They
are separated by a distance d.
At the midpoint between the spheres, the
magnitude of the electric field is:
1 8q
A. E 
40 d 2
1
2q
C. E 
40 d 2
1
4q
B. E 
40 d 2
1
q
D. E 
40 d 2
E. E  0
+q
+q
Clicker Question 4
Two identical spheres have charges +q. They
are separated by a distance d.
At the midpoint between the spheres, the
electric potential is:
1
4q
A. V 
40 d
1
q
C. V 
40 d
1
2q
B. V 
40 d
1
q
D. V 
40 2d
E. V  0
+q
+q
Answers
1E
2A
3E
4A
Class 8
Today we will:
• learn about static electric fields and electric
potentials in conductors.
• learn how charges move in regions where there
are electric and magnetic fields.
• learn about some practical devices that use
electric and magnetic fields.
Clicker Question 1
A net charge of +1.0 mC is placed on a steel ball.
The ball is then placed in the electric field of a
Van de Graaff generator. The total charge on the
surface of the steel ball is:
A. zero
B. + 0.5 mC
C. – 0.5 mC
D. + 1.0 mC
E. – 1.0 mC
Clicker Question 2
After a positive charge is “shot” into a region where
there is a uniform magnetic field, it spirals clockwise
out of the screen. If a negative charge were shot
into this region, it would:
A. spiral clockwise out of the screen
B. spiral clockwise into the screen
C. spiral counterclockwise out of the screen
D. spiral counterclockwise into the screen
Answers
1D
2C
Class 9
Today we will:
• learn about current, voltage, and power in
circuits.
• learn about resistance of materials and how
resistance depends on geometry and temperature.
• introduce Ohm’s law.
Clicker Question 1
What current passes through a 60 W light bulb?
(Line voltage is 120 V.)
A. 0.5 A
B. 1.0 A
C. 2.0 A
D. 7200 A
E. All of the above
Clicker Question 2
One block has resistance R. What is the
resistance when two blocks are joined at the
midpoints as shown:
A.R/2
B.R
C.3R/2
D.5R/4
E.2R
Clicker Question 2
One block has resistance R. What is the
resistance when two blocks are joined at the
midpoints as shown:
A.R/2
B.R
C.3R/2
D.5R/4
E.2R
Hint: Divide the combination into three regions.
Answers
1A
2D
Class 10
Today we will:
• learn how to determine if two resistors are in
series or parallel.
• find out how resistors combine when connected
in series and parallel.
• work examples of series-parallel reduction to
find current, voltage and power in resistance
networks.
Clicker Questions 1-6
Series-Parallel Quiz
Answer the following six questions
to see if you understand what
series and parallel mean.
1. Resistors A and B are in
1. series
2. parallel
3. neither
2. Resistors A and B are in
1. series
2. parallel
3. neither
3. Resistors A and B are in
1. series
2. parallel
3. neither
4. Resistors A and B are in
1. series
2. parallel
3. neither
5. Resistors A and B are in
1. series
2. parallel
3. neither
6. Resistors A and B are in
1. series
2. parallel
3. neither
Quiz Answers
1. series
2. neither
3. neither
4. parallel
5. series
6. parallel
Class 11
Today we will:
• discuss Kirchoff’s loop and node equations.
• learn how to determine the number of loop and
the number of node equations we will need.
• write Kirchoff’s equations for a sample circuit.
Clicker Question 1
A. I1  I 2  I 3
The junction equation for junction A is:
B. I 3  I1  I 6
C. I 3  I 6  I1
A
I1
D. I 3  I1  I 6
I3
E. I1  I 6  I 3  0
B
I6
D
I4
I5
I2
C
Clicker Question 2
The loop equation for loop 2 is:
A
I1
A.  I 6  I 3  6  I 5  I 6  0
+
B.  3I 6  2 I 3  6  6 I 5  7 I 6  0
I3
++
1
C.  3I 6  2 I 3  6  6 I 5  7 I 6  0
B
D.  3I 6  2 I 3  6  6 I 5  7 I 6  0 +
+
E.  3I 6  2 I 5  6 I 5  6 I 5  7 I 6  I04
I2
+
2
D
3
+
C
I5
+
I6
Answers
1C
2D
Class 12
Today we will:
• discuss test policies.
• review Lessons 1 – 4 to prepare for the exam.
Clicker Question 1
Your answer is 0.00467. What is the first
significant digit?
A: 0
B: 4
C: 5
Clicker Question 2
Your answer is 1.38×103. What is the
exponent?
A: 1
B: 2
C: 3
D: 4
Answers
1B
2C
Class 13
Today, we will:
• review characteristics of field lines and contours
• learn more about electric field lines and
contours of point charges
• learn more about magnetic fields and contours
of long, straight wires
Clicker Question 1
The strength of a field is given in terms of field
lines by:
A. the number of lines per unit length.
B. the number of contours per unit length.
C. the number of lines per unit area.
D.the number of contours per unit area.
Clicker Question 2
The wire law for magnetic fields is represented
geometrically by
A. the magnetic field lines.
B. the magnetic field contours.
C. the electric field lines.
D.the electric field contours.
Answers
1C
2B
Class 14
Today, we will:
• learn how to draw the total electric field of two
point charges.
• find that the electric field is like a single point in
the near field and the far field.
• use symmetry to find the electric field lines of
charged spheres, cylinders, and planes.
Clicker Question 1
Is this picture OK?
A – yes B -- no
+1
–1
Clicker Question 1
Is this picture OK?
A – yes B -- no
+1
–1
•Field lines can not cross.
•The near field is incorrect.
Clicker Question 2
Is this picture OK?
A – yes B -- no
+2
–1
Clicker Question 2
Is this picture OK?
A – yes B -- no
+2
–1
•The far field is incorrect.
•The near field isn’t drawn well.
Answers
1B
2B
Class 15
Today, we will:
• learn to visualize magnetic field lines for two
wires.
• learn to visualize electric and magnetic field
contours for two charges or wires.
Clicker Question 1
In three dimensions, the closed, blue lines are deformed:
A. loops
B. spheres
C. cylinders
D. disks
Clicker Question 2
In three dimensions, the elements of the field contour are
sections of:
A. loops
B. spheres
C. cylinders
D. disks
Answers
1B
2C
Class 16
Today, we will:
• learn what a capacitor is.
• learn the definition of capacitance.
• find the electric field and voltage inside a
parallel-plate capacitor.
• find the capacitance of the capacitor.
• learn that a dielectric is a material with polar
molecules.
• learn how dielectrics increase capacitance.
• find the energy stored in a capacitor and in the
electric field.
Clicker Question 1
A 4μF capacitor with a plate separation d is charged
by connecting it to a 6 V battery. The battery is
disconnected and the plates separated to 2d. The
new capacitance and voltage are:
A.
B.
C.
D.
E.
8 μF and 12 V.
8 μF and 3 V.
2 μF and 12 V.
2 μF and 3 V.
Nothing changes.
Q
E
0 A
C
0 A
d
Clicker Question 2
When compared to a capacitor with
no dielectric, adding a dielectric
A. always increases capacitance.
B. sometimes increases capacitance.
C. never increases capacitance.
Answers
1C
2A
Class 17
Today, we will:
• learn how to combine capacitors in series and
parallel
• find that circuits RC circuits have charges and
currents that depend on exponential functions
• learn the meaning of the exponential time
constant
• find that the exponential time constant for an RC
circuit is τ=RC
Clicker Question 1
What is the equivalent
capacitance of these
three capacitors?
3F
3F
A. 1F
B. 3F
C . 6 F
D. 9 F
E . 12 F
3F
3F
3F
3F
Clicker Question 2
What is the equivalent
capacitance of these
three capacitors?
A. 1F
B. 3F
C . 6 F
D. 9 F
E . 12 F
Clicker Question 3
What is the time constant of the
green (middle) curve?
A. 1 s B. 2 s C. 3s D. 4s E. 5 s
1
e
Answers
1A
2D
3C
Class 18
Today, we will:
• learn the definition of a Gaussian surface
• learn how to count the net number of field lines
passing into a Gaussian surface
• learn Gauss’s Law of Electricity
• learn Gauss’s Law of Magnetism
Clicker Question 1
What is the net number of field lines
passing through the Gaussian surface?
A. -8
B. -4
C. 0
D. +4
E. +8
Clicker Question 2
What is the net number of field lines
passing through the Gaussian surface?
A. -8
B. -4
C. 0
D. +4
E. +8
Clicker Question 3
What is the net number of field lines
passing through the Gaussian surface?
A. -8
B. -4
C. 0
D. +4
E. +8
Clicker Question 4
What is the net number of field lines
passing through the Gaussian surface?
A. -8
B. -4
C. 0
D. +4
E. +8
Clicker Question 5
What is the net number of field lines
passing through the Gaussian surface?
A. -8
B. -4
C. 0
D. +4
E. +8
Clicker Question 6
What is the net number of field lines
passing through the Gaussian surface?
A. -8
B. -4
C. 0
D. +4
E. +8
Answers
1E
2E
3A
4A
5C
6C
Class 19
Today, we will:
• learn how to use Gauss’s law and symmetry to
find the electric field inside a shperical charge
distribution
• show that all the static charge on a conductor
must reside on its outside surface
• learn that why cars are safe in lightning but cows
aren’t
Clicker Question 1
The magnitude of the electric field E(r) outside a
uniformly charged sphere (that means ρ is a constant) of
radius a is best represented by which of the following
graphs?
E(r)
E(r)
A.
B.
a
r
E(r)
E(r)
C.
D.
a
r
a
r
a
r
Clicker Question 2
The magnitude of the electric field E(r) inside a
uniformly charged sphere of radius a is best represented
by which of the following graphs?
E(r)
E(r)
A.
B.
a
r
E(r)
E(r)
C.
D.
a
r
a
r
a
r
Answers
1B
2A
Class 20
Today, we will:
• learn how integrate over linear, surface, and
volume charge densities to find the total charge on
an object
• learn that flux is the mathematical quantity that
tells us how many field lines pass through a
surface
Clicker Question 1
A cylinder of length L and radius R has a charge
density    z where  is a constant and z is
the distance from one end. Find the total charge on
the cylinder.
4
How do you slice the cylinder?
A. into cylindrical shells
B. into discs
C. into wedges
D. into rectangles
E. into rectangular prisms
Clicker Question 2
A cylinder of length L and radius R has a charge
density    z where  is a constant and z is
the distance from one end. Find the total charge on
the cylinder.
4
What is the volume of each slice?
A. dV  2rdz
B. dV  2Rdz
C. dV  2rLdr
D. dV  r dz
2
E. dV  R dz
2
Clicker Question 3
A cylinder of length L and radius R has a charge
density    z where  is a constant and z is
the distance from one end. Find the total charge on
the cylinder.
4
What are the limits of integration?
A. 0 to z
B. -z to +z
C. 0 to L
D. -L to +L
E. 0 to r
Clicker Question 4
A sphere of radius R has a charge density    r
where  is a constant. Find the total charge on the
sphere.
How do you slice the sphere?
A. into discs, sliced in the x-direction.
B. into discs, sliced in the y-direction.
C. into discs, sliced in the z-direction.
D. into spherical shells.
E. into wedges.
Clicker Question 5
A sphere of radius R has a charge density    r
where  is a constant. Find the total charge on the
sphere.
What is the volume of each slice?
A. dV  2rdr
B. dV  4R 2 dr
C. dV  4r dr
2
D. dV  r 2 dz
4 3
E. dV  r dr
3
Clicker Question 6
A sphere of radius R has a charge density    r
where  is a constant. Find the total charge on the
sphere.
What are the limits of integration?
A. 0 to R
B. 0 to r
C. –R to +R
D. –r to +r
E. all of the above
Answers
1B
2E
3C
4D
5C
6A
Class 21
Today, we will:
• learn how to use Gauss’s law to find the electric
fields in cases of high symmetry
• insdide and outside spheres
• inside and outside cylinders
• outside planes
Clicker Question 1
Gauss’s law states:
  EA 
qenc
0
The Gaussian surface we choose:
A.
B.
C.
D.
can be any surface
can be any closed surface
can be only an element of a field contour
can be only an element of a field contour
where the magnitude of the E field is the same
everywhere on the surface.
Clicker Question 2
Gauss’s law states:
  EA 
qenc
0
In this equation, A represents:
A. the surface area of the charged object.
B. the surface area of the Gaussian surface.
C. the surface area of Mars.
Clicker Question 3
Gauss’s law states:
  EA 
qenc
0
In this equation, qenc always represents:
A. the total charge of the object.
B. only the charge enclosed within the Gaussian
surface.
C. the charge of an electron.
D. the charge off an electron.
Answers
1D
2E
3C
Class 22
Today, we will:
• learn the meaning of an Amperian loop
• learn how to count the number of perpendicular
surfaces pierced by a line
• learn Ampère’s law: the net number of
perpendicular surfaces pierced by an Amperian
loop is proportional to the current passing
through the loop
• find how Ampère’s law and symmetry show that
the magnetic field inside a hollow wire is zero
• learn that the number of pierced surfaces is
mathematically represented by the line integral.
Clicker Question 1
What is the net number of surfaces pierced by this
Amperian loop?
A. -16
B. -8
C. 0
D. +8
E. +16
Clicker Question 2
What is the net number of surfaces pierced by this
Amperian loop?
A. -16
B. -8
C. 0
D. +8
E. +16
Answers
1E
2C
Class 23
Today, we will use Ampere’s law to find the
magnetic fields
• inside and outside a long, straight wire with
radial charge density
• of a plane of wires
• of a solenoid
• of a torus
Clicker Question 1
A wire of radius R has current density j   r.2 Find
the magnetic field inside the wire.
What is the correct expression for the ℓ in the line
integral?
A.    r
2
B.    R
C.   2 r
D.   2 R
2
E. None of the above.
Clicker Question 2
A wire of radius R has current density j   r.2 Find
the magnetic field inside the wire.
What is the correct expression for ienc ?
r
A. ienc    r 2 rdr
2
R
B. ienc    r 2 rdr
0
0
r
R
C. ienc    r 4 r dr
2
2
2
D. ienc    r 4 r dr
0
0
E. None of the above.
2
2
Clicker Question 3
A wire of radius R has current density j   r 2. Find
the magnetic field inside the wire.
A. B(r )  0
r
3
4
3
r
C. B(r )  0
3
B. B(r )  0
R
4
4r
3
R
D. B(r )  0
3
E. None of the above.
Clicker Question 4
A wire of radius R has current density j   r 2. Find
the magnetic field outside the wire.
A. B(r )  0
r
3
4
3
r
C. B(r )  0
3
B. B(r )  0
R
4
4r
3
R
D. B(r )  0
3
E. None of the above.
Answers
1C
2A
3A
4B
Class 24
Today, we will use direct integration to find
• electric fields of charged rods and loops
• electric potentials of charged rods and loops
• magnetic fields of current-carrying wire
segments and loop segments (Biot-Savart law)
Clicker Question 1
Are you here?
A.Yes
B. No
Clicker Question 2
Are you still here?
A.Yes
B. No
Answers
1A
2A
Class 25
Today, we will:
• learn the definition of divergence in terms of
flux.
• learn the definition of curl in terms of the line
integral.
•
• find the gradient, divergence, and curl in terms
of derivatives (differential operators)
• write Gauss’s laws and Ampere’s law in
differential form
• work several sample problems
Clicker Problem 1
You know both the electric and magnetic fields
in a region of space. If you wish to find the
volume charge density, you could use the
differential form of
A. Gauss’s law of electricity
B. Gauss’s law of magnetism
C. Ampere’s law
D. Faraday’s law
E. Coulomb’s law
Clicker Problem 2

12xy
j ( x, y )  
zˆ
0
Which picture best describes the current?
Take red to be out of the screen and blue
to be into the screen.
y
y
x
A
y
x
B
y
x
C
x
D
Answers
1A
2B
Class 27
Today we will:
• learn the definitions of electric and magnetic
dipoles.
•find the forces, torques, and energies on dipoles
in uniform fields.
•learn what happens when we put dipoles in
nonuniform fields.
Clicker Question 1
At what angle θ is the torque on the dipole
maximum?
A. 0° B. 45° C. 90° D. 135° E. 180°

B

A

Clicker Question 2
At what angle θ is the potential energy of
the dipole maximum?
A. 0° B. 45° C. 90° D. 135° E. 180°

B

A

Answers
1C
2E
Class 28
Today we will:
• define magnetization and magnetic susceptiblity
• learn about paramagnetic, diamagnetic, and
ferromagnetic materials
• learn about the opposing effects of domain
alignment and thermal disalignment
• learn how to understand hysteresis curves
• characterize ferromagnetic materials in terms of
residual magnetization and coercive force
Clicker Question 1
If this sphere is
uniformly charged,
it must be
N
A. positive
B. negative
C. neutral
S
Answers
1A
Class 29
Today we will:
•learn about threads and stubs of accelerating
point charges.
• learn that accelerating charges produce
radiation (except in quantum mechanics).
• learn the characteristics of radiation fields.
Clicker Question 1
If a charged particle has velocity in the +x
direction, but acceleration in the –x direction:
A.the threads get smaller in time
B.the threads get larger in time
C. I don’t want to think about it, it’s almost
Thanksgiving.
Clicker Question 2
If a charged particle has velocity in the +x
direction, but acceleration in the –x direction:
A.the threads become perpendicular to the head
line
B.the threads become parallel to the head line
Clicker Question 3
If a charged particle has velocity in the +x
direction, but acceleration in the –x direction:
A.the direction of the thread is the same as when
the particle’s acceleration is in the +x direction
B.the direction of the thread is in the opposite
direction to that when the particle’s acceleration
is in the +x direction
Answers
1B
2A
3B
Class 30
Today we will:
•learn how accelerating charges affect circuits in
significance ways
•learn about induced electric fields
•learn about induced magnetic fields and
displacement current
•learn Faraday’s Law
•learn Maxwell’s Term of Ampere’s Law
Clicker Problem 1
What is the direction of the electric
acceleration field?
A.right
P
B.left

C.in
R
D.out
E.up

a
i
Clicker Problem 2
What is the direction of the magnetic
acceleration field?
A.right
P
B.left

C.in
R
D.out
E.up

a
i
Clicker Problem 3
 
What is the direction of E  B ?
A. right
B. left
P
C. in

D. out
R
E. up

a
i
Answers
1B
2D
3E
Class 31
Today we will:
• learn about EMF
• learn how Faraday’s law works
• learn Lenz’s Law and how to apply it
Clicker Question 1
What happens if all sides
of the loop move
together?
A. Current flows.
B. Current doesn’t flow.

B

v

v
Clicker Question 2
• The external B is into the screen and is constant.
• A copper wire is placed in the field and rotated
about the axis shown. In what direction is the
induced current?
A. cw
B. ccw
C. depends on the
direction of rotation
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Bexternal
Answers
1B
2A
Class 32
Today we will:
• work several Faraday’s law problems
• learn about Eddy currents
Class 32
No new questions…
Class 33
Today we will:
•learn how motors and generators work
•learn about split commutators and their use in
DC motors and generators
Clicker Question 1
The flux through the loop is:
A.  B  BA
B.  B  B cos 
C.  B  A cos 
D.  B  AB cos 

B


A
Clicker Question 2
If we rotate the handle with angular speed  ,
A.   t
B.    / t
C.   t / 

B


A
Clicker Question 3
If we rotate the handle with angular speed  ,
the EMF is:
A.   BA cos t
B.   BA  sin t
C.    BA  sin t
D.  
BA

E.   
sin t
BA

sin t

B


A
Answers
1D
2A
3B
Class 34
Today we will:
•learn about inductors and inductance
•learn how to add inductors in series and parallel
•learn how inductors store energy
•learn how magnetic fields store energy
•learn about simple LR circuits
Clicker Question 1
The direction of induced current will be
A.always opposite the direction
of the current from the battery.
B. always in the direction of
the current from the battery.
V

C. possibly in either direction.
N
L
R
Clicker Question 2
The inductive time constant will be proportional to
A. LR
B. L/R
C. R/L
D. 1/(LR)
Answers
1C
2B
Class 35
Today we will:
•learn more about LR circuits
•learn the LR time constant
•learn about LC circuits and oscillation
•learn about phase angles
Clicker Question 1
The voltage around the circuit loop at any
given time must be:
A. positive
B. negative
C. zero

V



L
R


Clicker Question 2
If the current is decreasing, the
inductor will
V
A. cause the current to
decrease faster
B. cause the current to
R
decrease more slowly
C. not affect the rate the
current decreases
1

2
L
Answers
1C
2B
Class 36
Today we will:
•learn about phasors
•define capacitive and inductive reactance
•learn about impedance
•apply Kirchoff’s laws to AC circuits
Clicker Question 1
The phasor to the right represents:
A.
B.
C.
D.
E.
1.5 sin 60
2.7 sin 30
3 sin 30
3 cos 30
None of the above
Clicker Question 2
Which of the following is a phasor diagram for a
capacitor, and inductor, and a resistor in series?
Blue is voltage, red is current.
A.
B.
C.
D.
Answers
1C
2C
Class 37
Today we will:
• study the series LRC circuit in detail.
• learn the resonance condition
• learn what happens at resonance
• calculate power in AC circuits
Clicker Question 1
What is the same for each element in the
circuit?
0
A. The magnitude of the voltage
B. The magnitude of the current
C. The current phasor
D.The voltage phasor

R
i
L
C
Answers
1C
Class 38
Today we will:
• find out how transformers work
• learn about how electrical power is generated
and delivered to our homes.
Clicker Question 1
A transformer has 100 turns in its
primary coil and 200 turns in its
secondary coil. The voltage across the
primary coil is 12.0 V. The voltage across
the secondary coil is:
A. 3.0 V
B. 6.0 V
C. 12.0 V
D. 24.0 V
E. 48.0 V
Clicker Question 2
A step up transformer provides greater
voltage in the primary and the secondary.
This implies that
A. energy is not conserved in electrical
circuits.
B. energy is not conserved in transformers.
C. the secondary cannot provide as much
current as the primary.
D. the secondary can provide more current
than the primary.
Answers
1D
2C
Class 39
Today we will:
• learn about wires used in homes
• learn how switches and outlets are wired
• learn how to wire a 3-way switch
• find out about safety devices: grounds, GFCI’s,
and AFCI’s
Clicker Question 1
If one switch is up and the other is down:
A. the light is off.
B. the light is on.
C. It depends on which switch is up and which is down.
down
down
Clicker Question 2
Most of the current flows:

big
resistance
A. through the ground wire
B. through you
C. through the toast
D. you are toast
small
resistance
Answers
1A
2A
Class 40
Today we will:
• review basic characteristics of waves
• introduce definitions of wave terminology
• show how Maxwell’s Equations predict
electromagnetic waves
• discuss the spectrum of electromagnetic
radiation
• learn how radio antennas send and receive
signals
Clicker Question 1
If a wave has a wavenumber of k=4,
what is its wavelength?
A.
B.
C.
D.
E.
π/4
π/2
π
2π
4π
Clicker Question 2
What is the wavelength of an FM radio
wave that has a frequency of 100 MHz?
A. 3 m
B. 3 cm
C. 3 mm
D. 3 μm
E. 3 nm
Answers
1B
2A
Class 41
Today we will:
• learn how digital information is transmitted on
electromagnetic waves
• learn the meaning of polarization
• learn about polarized light and its applications
Clicker Question 1
Which figure best represents the wave along the z axis?
C
A
B
D
Red is E, blue is B.
Clicker Question 2
Unpolarized light passes through
1)a polarizing filter
2)a second polarizing filter at 45° with respect
to 1.
3)a third polarizing filter at 45° with respect to 2.
Does any light emerge?
A. yes
B. no
Answers
1C
2A