Recitation ch 31
Answers at the end

Question 1
A square loop of wire lies in the plane of the page.
A decreasing magnetic field is directed into the page.
The induced current in the loop:

      a   is counterclockwise.
      b   is clockwise in two of the loop sides and counterclockwise
         in the other two.
      c   depends upon whether or not B is decreasing
         at a constant rate
      d   is clockwise.
      e   is zero.
Question 2
A rectangular loop of wire is placed midway between two long
straight parallel conductors as shown in figure (11). The
conductors carry currents i1 and i2 as indicated. If i1 is
increasing and i2 is constant, then the induced current in
the loop is:

      a   depends on i1 + i2.
      b   counterclockwise.
      c   zero.
      d   depends on i1 - i2.
      e   clockwise.
Question 3
A 200-turn coil has a cross sectional area of 0.20 m**2
and a resistance of 20 ohms. The coil is placed in a
magnetic field perpendicular to the plane of the coil.
The magnitude of the magnetic field decreases from
1.6 milli-T to zero in 0.020 seconds.
What is the current induced in the coil ?

      a   32.0 mA
      b   3.20 mA
      c   16.0 mA
      d   160 mA
      e   0.800 mA
Question 4
A long straight wire is in the plane of a rectangular
conducting loop as shown in Figure 8. The straight
wire carries an increasing current i in the direction
shown. The current in the rectangular is:

      a   counter clockwise in the left side and clockwise
         in the right side.
      b   zero.
      c   counter clockwise.
      d   clockwise.
      e   clockwise in the left side and counter clockwise in
         the right side.
Question 5
The circuit shown in figure 9 is in a uniform magnetic field
that is into the page and is decreasing in the magnitude
at the rate of 150 T/s. The current in the circuit is:

      a   0.15 A.
      b   0.22 A.
      c   0.18 A.
      d   0.62 A.
      e   0.40 A.
Question 6
Figure 12 shows a conducting loop consisting of a half circle of
radius 0.20 m and three straight sections. The loop lies in a
uniform magnetic field that is directed as shown in the figure
and is given by: B = (4.5*t**2) - (10*t) , with B in tesla and t
in seconds.
What is the magnitude of the induced emf at t = 10 s ?

      a   10 V
      b   5.0 V
      c   4.1 V
      d   6.3 V
      e   8.2 V
Question 7
A 2.0-T uniform magnetic field (in the x-y plane) makes an angle
of 30 degrees with the y-axis. The magnetic flux through
a 4.0-m**2 portion of the xz plane is:

      a   6.9 Wb
      b   4.0 Wb
      c   12 Wb
      d   3.0 Wb
      e   8.0 Wb
Question 8
Figure 10 shows a bar moving to the right on two conducting
rails. To make an induced current in the direction
indicated, a constant magnetic field in region A should
be in what direction?

      a   Left.
      b   Impossible; this cannot be done with a constant
         magnetic field.
      c   Right.
      d   Out of the page.
      e   Into the page.
Question 9
The square coil shown in figure(12) is 20 cm on a side and
has 15 turns of wire on it. It is moving to the right at
2 m/s. Find the induced emf in it at the instant shown,
and the direction of the induced current in the coil. (The
magnetic field is 0.2 T and its direction is out of the page.)

      a  3.6 V, counter-clockwise
      b  zero
      c  1.2 V, clockwise
      d  1.2 V, counter-clockwise
      e  3.6 V, clockwise
Question 10
A metal rod of resistance 12 ohms is forced to move with
constant velocity along two parallel metal rails as shown
in figure 13. A magnetic field of magnitude 0.35 T is
directed as shown in the figure. The separation between the
rails is 25.0 cm and the speed of the rod is 45.0 cm/s.
What is the current in the rod ?
Neglect the resistance of the rails.

      a   1.43 mA counterclockwise
      b   1.43 mA clockwise
      c   3.28 mA clockwise
      d   2.32 mA clockwise
      e   3.28 mA counterclockwise
Question 11
A long straight wire is parallel to one edge and is in the plane
of a rectangular conducting loop as shown in figure 11.
The straight wire carries a constant current. While the wire is
being moved toward the loop, the current induced in the loop is

      a   clockwise.
      b   decreasing.
      c   always equal to the current in the wire.
      d   zero.
      e   counterclockwise.

1     d
2     b
3     d
4     c
5     b
6     e
7     a
8     e
9     c
10     c
11     e