SP212/3321&5521
Chapter 30 - Worksheet #2
Question 1: A wire loop with mass m=0.450 kg, total resistance R=12.0 Ω, and width L=0.150 m
is held with its top in a uniform magnetic field of strength B=3.50 T directed into the page. The
loop is dropped, and falls downward due to gravity. (a) As the loop falls downward, what is the
direction (clockwise or counter-clockwise) of the induced current in the loop? (b) What terminal
speed does the loop reach? (i.e. At what constant speed will the loop stop accelerating downward?)
(c) When the loop is falling at its terminal speed, at what rate is the resistor dissipating heat? (i.e.
At what rate is gravitational potential energy being converted into thermal energy?)
0.150 m
~
B
×
~g
12.0 Ω
SP212/3321&5521
Chapter 30 - Worksheet #2
Question 2: The current flowing through the 7.50 mH inductor shown below is given by
i(t) = 2.5t2 − 3.0t + 0.9, where i has units of amperes when t has units of seconds and a
positive current indicates current flowing to the right. What is the potential difference, Vb − Va ,
across this inductor at time t=0.35 s? [Reminder: Vb −Va will be positive if the induced emf points to
the left (opposite the current) and negative if the induced emf points to the right (with the current).]
i
7.50
mH
b
a
Question 3: A solenoid wrapped with N =650 turns is 0.350 m long and has a cross-sectional area
of 0.00150 m2 . (a) What is the inductance of this solenoid? Suppose that a current of 1.25 A flows
through the solenoid. (b) What is the magnitude of the magnetic field inside the solenoid? (c) What
is the average magnitude of the induced emf across the solenoid if the current is increased to 3.25 A
over a time period of 12.0 s?