Chapter 22: Magnetic Induction & Lenz’s Law
Example Problems

motional
 vLB
B  A eff B  ABcos 

induced
N
B
t
Example 22.1
A I5-cm-long metal rod is pulled along two frictionless conducting rails at a constant
speed of 3.5 m/s. The rails have negligible resistance, but the rod has a resistance of
0.65Ω.
a. What is the current induced in the rod?
b. What force is required to keep the rod moving at a
constant speed?
Example 22.2
A loop of wire has the shape shown in the drawing. The top part of
the wire is bent into a semicircle of radius r = 0.20 m. The normal
to the plane of the loop is parallel to a constant magnetic field (φ
= 08) of magnitude 0.75 T. What is the change ∆Φ in the
magnetic flux that passes through the loop when, starting with the
position shown in the drawing, the semicircle is rotated through
half a revolution?
Example 22.3
Parts a through f of figure show one or more metal wires sliding on fixed metal rails in a
magnetic field. For each, determine if the induced current is clockwise,
counterclockwise, or is zero.
Example 22.4
The loop in figure has an induced current as shown. The loop
has a resistance of 0.10Ω. Is the magnetic field strength
increasing or decreasing? What is the rate of change of the field
(∆B/∆t)?