Physics 4U
Unit 3 Test (Chapters 6, 7 and 8)
Kitty Wu
TEST Verson1
TOTAL:
/40
Multiple Choices (2 points each; 20 points total): Please choose the best answer for each of the
following questions.
1. If both the radius and mass of a planet were to double, the magnitude of the gravitational field
strength at its surface would become
a) Halved
b) Unchanged
c) Doubled
d) Depends on the mass of the object on the surface
e) Four times as much
2. If the mass of the Sun were to become half its current value, with Earth maintaining its same
orbit, the time interval of one Earth year would
a) Remain the same
b) Decrease by a factor of √2
c) Increase by a factor of √2
d) Increase by a factor of 2
e) Decrease by a factor of 2
3. A satellite in geosynchronous orbit has a period of revolution of
a) 1.5 h
b) 1.0 h
c) 24 h
d) 365.26 d
e) None of these
4. Satellite S1 is moving around Earth in a circular orbit of radius four times as large as the radius of
the orbit of satellite S2. The speed of S1, v1 in terms of v2 equals
a) 16v2
b) v2
c) 2v2
d) 0.5v2
e) None of these
5.
The magnitude of the magnetic field 20cm from a straight wire with a current of 12A is
a) 1.8×10−5
b) 2.4×10−6
c) 1.8×10−7
d) 1.2×10−6
e) 1.2×10−5
f) None of these
6. A 1nC positive point charge is located at point A. The electric potential at point B is
Physics 4U
a)
b)
c)
d)
e)
Unit 3 Test (Chapters 6, 7 and 8)
Kitty Wu
9V
9V·sin 30°
9V·cos 30°
9V·tan 30°
None of these
7. An electron is released from rest at point B, where the potential is 0 V. Afterward, the electron
a)
b)
c)
d)
e)
Moves toward C with increasing speed.
Moves toward A with increasing speed.
Moves toward C with steady speed.
Remains at rest at B.
Moves toward A with steady speed.
8. Two charges, –2Q and +Q, are located on the x–axis, as shown. Point P, at a distance of 3D from
the origin O, is one of two points on the positive x–axis at which the electric potential is zero.
How far from the origin O is the other point?
a)
b)
c)
d)
e)
2/3 D
D
3/2 D
5/3 D
2D
9. There are 5 balls labelled A, B, C, D, and E. A and B repel each other. A and C attract each other.
D and E attract each other. Which of the following is impossible?
a) B repels D and C repels E.
b) Several of the other situations are impossible.
c) A attracts D and B attracts E.
d) A repels D and B repels E.
e) A attracts D and C repels E.
Physics 4U
Unit 3 Test (Chapters 6, 7 and 8)
Kitty Wu
10. A wire carries current in the plane of this paper toward the top of the page. The wire
experiences a magnetic force toward the right edge of the page. What is the direction of the
magnetic field causing this force?
a) Upward out of the page
b) Downward into the page
c) In the plane of the page and toward the left edge
d) In the plane of the page and toward the bottom edge
e) In the plane of the page and toward the right edge
f) None of above
Problem solving (15 points total):
1. A coil 8.0 cm long, with 400 turns, produces a magnetic field of magnitude 1.4 x 10–2 T in its
core. Calculate the current in the coil. ( o=4x10-7 T m / A ) (7 points)
2. A uniform magnetic field B, with magnitude B = 1.2 x 10-3 T, points vertically upward throughout
the volume of a laboratory chamber. A proton with a velocity v = 3.2 x 107 m/s enters the
laboratory moving horizontally from south to north. Find (a) the magnitude and (b) the direction
of magnetic force on the proton. ( proton charge q=1.6x10-19C) (8 points)
(a) F = q v B = (1.6x10-19C )•( 3.2 x 107 m/s )•( 1.2 x 10-3 T) =6.14 x10-15 N
(b) Direction would be east by right hand rule
Word problem (5 points):
Suppose that electric field E=0V/m through some region of space. Can you conclude that the electric
potential V=0V in this region? Explain.
No, we cannot conclude V=0V.
Electric field E is equal to the change in V, V could be some non-zero constant in a region to have E=0
Physics 4U
Unit 3 Test (Chapters 6, 7 and 8)
Kitty Wu
TEST Verson2
TOTAL:
/40
Multiple Choices (2 points each; 20 points TOTAL): Please choose the best answer for each of the
following questions.
1. Two isolated electrons starting from rest move apart. Which of the following statements is true
as the distance between the electrons increase?
a) The velocity increases and the acceleration is constant
b) The velocity increases and the acceleration decreases
c) The velocity decreases and the acceleration is constant
d) The velocity increases and the acceleration increases
e) The velocity is constant and the acceleration is constant
2. Pictured below are two charges. Assume they are both on the x-axis. At what location(s) a finite
distance away, along the x-axis, is/are the electric field zero?
a)
b)
c)
d)
e)
Somewhere between the two charges.
There are multiple such locations.
Somewhere to the right of both charges.
Somewhere to the left of both charges.
There are no such locations.
3. A horizontal wire carries a current straight toward you. From your point of view, the magnetic
field caused by this current
a) Points directly away from you.
b) Points toward you
c) Points to the left.
d) Circles the wire in a clockwise direction.
e) Circles the wire in a counter-clockwise direction.
4. A pair of disks of radius R and a small distance d apart from a capacitor. One plate is given a
charge of +Q and the other plate is given a charge of -Q. If the charge is unchanged, but both R
and d are doubled, what happens to the magnitude of the electric field inside the capacitor?
a) It decreases by a factor of 2.
b) It increases by a factor of 2.
c) It decreases by a factor of 8.
d) It remains the same.
e) It decreases by a factor of 4.
5. An electron moves in the plane of this paper toward the top of the page. A magnetic field is also
in the plane of the page and directed toward the right. What is the direction of the magnetic
force on the electron?
a) Toward the top of the page
b) Toward the bottom of the page
c) Toward the left edge of the page
d) Toward the right edge of the page
e) Upward out of the page
f) Downward into the page
Physics 4U
Unit 3 Test (Chapters 6, 7 and 8)
Kitty Wu
6. A wire carries current in the plane of this paper toward the top of the page. The wire
experiences a magnetic force toward the right edge of the page. What is the direction of the
magnetic field causing this force?
a) In the plane of the page and toward the left edge
b) In the plane of the page and toward the bottom edge
c) Upward out of the page
d) Downward into the page
e) In the plane of the page and toward the right edge
f) None of above
7. For the capacitor shown in the figure below, the potential difference ΔVab between points
a and b is,
a)
b)
c)
d)
e)
f)
6 sin30°V
6V
6 cos30° V
6 /cos30° V
6 tan30° V
6 /sin30° V
8. An electron travels from just beside a positively charged plate to a location just beside a
negatively charged plate. What happened?
a) It's electric potential increased while its speed increased.
b) None of the other answers are correct.
c) It's electric potential increased while its speed decreased.
d) It's electric potential decreased while its speed increased.
e) It's electric potential decreased while its speed decreased.
9. Satellite S1 is moving around Earth in a circular orbit of radius four times as large as the radius of
the orbit of satellite S2. The speed of S1, v1 in terms of v2 equals
a) 16v2
b) v2
c) 2v2
d) 4v2
e) None of these
10. A positive electric charge is moved at a constant speed between two locations in an electric
field, with no work done by or against the field at any time during the motion. This situation can
occur only if the
a) Charge is moved in the direction of the field
Physics 4U
b)
c)
d)
e)
f)
Unit 3 Test (Chapters 6, 7 and 8)
Kitty Wu
Charge is moved opposite to the direction of the field
Charge is moved perpendicular to an equipotential line
Charge is moved along an equipotential line
Electric field is uniform
Not possible
Problem solving (14 points TOTAL):
1. Calculate the magnitude of the magnetic field strength in the core of a coil 10.0 cm long, with
420 turns and a current of 6.0 A. ( o=4x10-7 T m / A) (6 points)
2. A proton has a speed of 3.0X106 m/s in a direction perpendicular to a uniform magnetic field,
and the proton moves in a circle of radius 0.20 m. What is the magnitude of the magnetic field?
( proton charge q=1.6x10-19C) (8 points)
qvB=
𝑚𝑣 2
𝑟
B=
𝑚𝑣 2
𝑞𝑣𝑟
=
𝑚𝑣
𝑞𝑟
= 0.16 𝑇
Word problem (6 points TOTAL):
Suppose that the electric potential V=0V through some region of space. Can you conclude that
electric field E=0V/m in this region? Explain. What about if V=2V?
Yes. If V has any constant value throughout a region of space, then electric field e is 0.