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Instructor(s): F.E. Dunnam, G. Mitselmakher
PHYSICS DEPARTMENT
PHY 2054
2nd Exam
Name (print, last first):
22 March 2005
Signature:
On my honor, I have neither given nor received unauthorized aid on this examination.
YOUR TEST NUMBER IS THE 5-DIGIT NUMBER AT THE TOP OF EACH PAGE.
(1) Code your test number on your answer sheet (use 76–80 for the 5-digit number). Code your name on your
answer sheet. DARKEN CIRCLES COMPLETELY. Code your UFID number on your answer sheet.
(2) Print your name on this sheet and sign it also.
(3) Do all scratch work anywhere on this exam that you like. Circle your answers on the test form. At the end of
the test, this exam printout is to be turned in. No credit will be given without both answer sheet and printout with
scratch work most questions demand.
(4) Blacken the circle of your intended answer completely, using a #2 pencil or blue or black ink. Do not
make any stray marks or some answers may be counted as incorrect.
(5) The answers are rounded off. Choose the closest to exact. There is no penalty for guessing.
(6) Hand in the answer sheet separately.
Constants
2
µ0 = 4π × 10−7 Tm
g = 9.80 m/s2
e = 1.6 × 10−19 C
1µC = 10−6 C
A
9
2
2
−31
6
kE = 8.99 × 10 Nm /C
me = 9.11 × 10
kg
M = “mega” = 10
1nC = 10−9 C
mp = mn = 1.67 × 10−27 kg
c = 3 × 108 m/s
²0 = 8.85 × 10−12 C2 /N/m2 1pC = 10−12 C
1. A conducting rod is 0.5 m long and has a mass of 100 kg. What is the minimum current (in A) in the rod that can
cause it to float in a horizontal magnetic field of 1 T?
(1) 1.96
(2) 0.98
(3) 2.18
(4) 0.36
(5) 0.18
2. A particle with a −4.0µC charge and a kinetic energy of 0.18 J moves in a circular path of radius 3 m in a uniform
magnetic field of 1 T. Determine the mass of the particle, in kg.
(1) 4 × 10−10
(2) 2 × 10−12
(3) 3 × 10−8
3. Two long straight wires separated by 0.1 m carry currents of 18A
and 6A in the opposite directions as shown. Determine the magnetic field (in T) at point P.
(4) 1.8 × 10−10
I1
(5) 6 × 10−9
= 18 A
I2
= 6 A
0.1 m
P
0.05 m
(1) 0
(2) 1.2 × 10−3
(3) 0.8 × 10−3
4. A 2.0 kg rod has a length of 1 m and a resistance of 4.0Ω. It slides
with constant speed down a pair of frictionless vertical conducting
rails that are joined at the bottom. A uniform magnetic field of
magnitude 3.0T is perpendicular to the plane formed by the rod
and the rails as shown. Determine the speed of the rod (in m/s).
(1) 8.7
(2) 0.9
(3) 0.38
(5) 2.18 × 10−3
(4) 0.12
1 m
x
x
x
x
v=const
x
x
x
x
x
x
(4) 2.6
m = 2 kg
Ω
R = 4
B = 3 T
(5) 5.6
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5. A uniform 3 T magnetic field is normal to the plane of a conducting, circular loop with a resistance of 1.5Ω and a radius of 0.024 m.
What is the average current, in A, around the loop if the magnetic
field is doubled in 0.4 s?
(1) 9.0 × 10−3 , clockwise
(2) 2.8 × 10−3 , clockwise
−3
(5) 4.5 × 10 , counterclockwise
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
(3) 4.5 × 10−3 , clockwise
B
.
(4) 9.0 × 10−3 , counterclockwise
6. Two conductive loops carry equal currents I in the same direction
as shown. If the current in the upper loop suddenly drops to zero,
what will happen to the current in the bottom loop?
(1)
(2)
(3)
(4)
(5)
the
the
the
the
the
current
current
current
current
current
will
will
will
will
will
I
increase.
decrease.
not change.
also drop to zero.
reverse its direction.
I
S
7. Consider the circuit in the figure, E = 6V, L = 8mH, R = 4Ω.
What is the maximum energy stored in the inductor after the
switch is closed?
L
R
(1) 9 × 10−3
(2) 5 × 10−3
(3) 4 × 10−2
8. A 0.10 m long solenoid has a radius of 0.05 m and 1.5 × 104 turns.
The current in the solenoid changes at a rate of 6.0 A/s. A conducting loop of radius 0.02 m is placed at the center of the solenoid
with its axis the same as that of the solenoid, as shown. Determine
the induced emf in the loop (in V).
(1)
(2)
(3)
(4)
(5)
(4) zero
(5) infinite
loop
I
I
1.4 × 10−3
0.7 × 10−3
2.8 × 10−3
5.6 × 10−3
zero
9. A copper rod with a weight per unit length of 0.04 N/m is suspended directly above a second copper rod. The bottom
rod carries a current of 100 A. The top rod is held in place by magnetic repulsion at a distance of 9 mm from the
bottom rod. What is the current (in A) in the top rod?
(1)
(2)
(3)
(4)
(5)
18 A
30 A
60 A
72 A
100 A
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10. An electromagnetic wave in vacuum has an electric field amplitude of 440 V/m. Calculate the corresponding magnetic
field, in T. (Speed of light c = 3.0 × 108 m/s)
(1) 1.5 × 10−6
(2) 3.0 × 10−6
(3) 0.18 × 10−6
(4) 2.3 × 10−6
(5) 4.5 × 10−6
11. Note the different types of electromagnetic radiation:
1. x-rays
2. radio waves
3. gamma rays
4. visible light
5. infrared radiation
6. ultraviolet radiation
Which list correctly ranks the electromagnetic waves in order of increasing frequency?
(1) 2, 5, 4, 6, 1, 3
(2) 2, 5, 4, 1, 6, 3
(3) 2, 3, 4, 5, 6, 1
(4) 3, 1, 6, 4, 5, 2
(5) 3, 6, 1, 4, 5, 2
12. An underwater scuba diver sees the sun at an apparent angle of 30◦ from the vertical. How far is the sun above the
horizon (in degrees)? (nwater = 1.333)
(1) 41.6
(2) 22.0
(3) 48.2
(4) 51.8
13. Three mirrors are arranged as shown. The light strikes the first
mirror at an angle d = 30◦ with respect to mirror 1. At what
angle β does the light exit after being reflected from mirror 3?
(5) 60.0
α = 30
o
o
110
β=?
o
90
(1) 50◦
(2) 40◦
(3) 60◦
(4) 30◦
14. The current I = 10A is flowing in a clockwise direction in a triangular loop of wire in the plane of the paper as shown. The bottom
side of the triangle is parallel to a magnetic field of 2T directed
from left to right. What is the net magnetic force acting on the
loop (in N)?
(5) 20◦
30
I = 10A
o
I
B = 2T
o
60
1 m
(1) zero
(2) 34
(3) 20
(4) 14
(5) 86
15. An electron traveling due north enters a region that contains both a magnetic field and an electric field. The electric
field lines point due west. It is observed that the electron continues to travel in a straight line due north. In which
direction must the magnetic field point?
(1) up
(2) down
(3) east
(4) west
(5) south