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Scheller
Physics 176
Exam #3
Spring 2016
9 a.m.
Read these instructions carefully. Write your name in the upper right hand corner of this page. Answers
without units are incomplete.
Constants:
1)
μ0=4π x 10-7 Tm/A
vlight=3x108 m/s
vsound= 343m/s
qe= 1.6x10-19 Coulombs
An electron experiences the greatest force as it travels 6.3x106 m/s in a magnetic field when it is
moving northward. The force is 0.7 N and is directed upwards away from the ground. What are the
magnitude and direction of the magnetic field?
6.94x10-11T, East
2)
Two wires carrying currents of 10 A and 12 A are situated as shown.
a) What is the magnitude and direction of the magnetic field at
point P due to these two wires?
12 A
5 cm
10 A
5 cm
3.44x10-5T at 35.80 N of W
p
b) What would be the force on a 2 m wire carrying 7 A into the
page at point P if I placed it there?
4.82x10-4 N at 35.80 E of N
3)
Indicate the direction of the induced current in the square coil as it is moved through the magnetic
field in positions a) – e) as shown.
A
a)
b)
c)
d)
e)
none
CCW
none
CW
none
A
B
C
D
E
4)
A round coil of radius 10 cm has 50 turns and sits perpendicular to a B-field
of 0.8 T as shown. If the coil is removed from the field in 0.05 seconds,
what is the:
a) Change in flux, , in the coil?
b) Induced voltage and current if the resistance is 40?
c) Direction of the induced current?
-.0251 Wb
25.1 V, .628 A
CCW
5)
A coil with 200 turns on a square frame of sides 18 cm sits at an angle of 30 relative to a B-field that
changes from 0.75 T to 0.25 T in 0.8s. The coils resistance is 2 .
a) What is the induced voltage in the coil when the
field changes?
b) What power is dissipated in the coil when the field
300
B
changes?
3.51 V
6.15 W
6)
2.5 A
.35%
600
An AC power generator produces 50 amps of current at 3600 V. The voltage is stepped up to 72,000V
by an ideal transformer and the energy is transmitted through a long-distance power line with a
resistance of 100 .
a) At what current is the power being transmitted?
b) What percentage of the input power is lost in the power line?
c) If there are 30 turns in the primary coil, how many turns are there in the secondary?
7)
A new cordless phone emits 4.0 milliwatts of power at a frequency of 5.8x109 Hz.
a) What is the wavelength of this radiation?
.0517 m
b) If we assume the signal from this phone spreads out evenly in all directions, what is the maximum
electric field strength and maximum magnetic field strength 30 m from the phone?
5.44x10-11 T
.015 V/m