School of science and Engineering
Al Akhawayn University
Test 2 (B)
Phy1402, Fall 2001
Instructor: Dr. H. Darhmaoui
Date: November 30, 2001
1. When two unknown resistors are connected in series with a battery, 250 W is dissipated with a total
current of 5.00 A. For the same total current, 60.0 W is dissipated when the resistors are connected in
parallel. Determine the values of the two resistors.
2. A magnetic field passes through a stationary wire loop of 150 turns, an area of 0.15 m2 and a resistance
of 0.50 Ω. The magnitude of the field changes in time according to the graph in Figure 1. The direction
of the field remains constant, however. There are three time intervals in the figure: 0 -3.0 s, 3.0-5.0 s,
and 5.0-6.0 s.
a. For each interval of time, determine the magnitude of the induced emf and the induced current in
the loop.
b. If the field is directed in the positive z-axis and the loop is at rest in the x-y plane, what is the
direction of the induced current during each interval? In all cases, provide a reason for your
answers.
B(T)
0.6
0
t (s)
0
3.0
5.0
6.0
Figure 1
3. Two parallel rails having negligible resistance are 20.0 cm apart and are connected by a 2.00 Ω
resistor. A uniform 0.01 T magnetic field is applied perpendicular to the plane of the rails. Find the
magnitude and direction of the current in the 2.00 Ω resistor in each of the following cases:
a) A metallic rod of resistance 15.0 Ω is sliding to the left at a constant speed 2.00 m/s as in Figure
2-a.
b) A metallic rod of resistance 10.0 Ω is sliding to the right at a constant speed 4.00 m/s as in Figure
2-b.
c) Both rods are sliding along the rails and moving away from the resistor at the constant velocities
shown as in Figure 2-c.
x 15.0 Ω
x
2.00 m/s
x
x
x
Figure 2
x 2.00 Ωx
x
x
x
x
x
x
x
B
B
x
x
x
x
x
x
(a)
x
x
2.00 m/s
x
x
x
x
x
x
x
x
15.0 Ω
x 2.00 xΩ
x
x
x
x
B
x
x
x
x
(c)
x
x
x
x
x
x 2.00 Ω x
x
x
x
x
B
B
x
x
x
x
(b)
x 10.0 Ω x
x
x
4.00 m/s
x
x
B
x
x
x
x
10.0 Ω
x
x
x
x
x
x
x
4.00 m/s
x
x
x