PHY2054 - Exam 3 - Fall 1997 - Selman Hershfield
To give everyone the benefit of a doubt, I have counted two answers
as correct for three of the problems. These answers are listed
in red below.
- A rectangular loop is placed next to a long wire
as shown in Fig. 1. If the current in the wire is
6A and the current in the loop is 10A, what is the
magnitude of the force on the loop?
- 1.2 x 10-5 N
- 2.4 x 10-5 N
- 3.6 x 10-5 N
- 4.8 x 10-5 N
- 7.2 x 10-5 N
- Four wires are placed at the corners of a
square with currents flowing either in or out of
the page as indicated in Fig. 2. If the magnitude of
the current in each wire is the same, what is the direction
of the magnetic field at the center, C, of the square?
- 45 degrees
- 90 degrees
- 135 degrees
- 225 degrees
- 315 degrees
- Two parallel wires carry currents of 1A and 2A
as indicated in Fig. 3. In which of the three regions,
I, II, or III, is there a point where the magnetic field
is zero?
- I only
- II only
- III only
- I and III
- I, II, and III
- A rectangular loop is placed next to a long wire as
shown in Fig. 1. What is the direction of the induced
current in the loop for the following two cases:
(i) the current, I, in the wire increases and
(ii) the current in the wire is kept constant but the
rectangular loop is moved further away from the wire
(to the right)?
- (i) clockwise (ii) clockwise
- (i) clockwise (ii) counterclockwise
- (i) counterclockwise (ii) clockwise
- (i) counterclockwise (ii) counterclockwise
- none of the above
- A magnetic field of 0.3 Tesla is rotated relative to a loop
of wire from the angle shown
in Fig. 4(a) to the angle shown in Fig. 4(b) in 2 seconds.
If the loop of wire forms a circle with radius 13 cm and
has resistance of 250 Ohms, what is the average current
induced in the loop?
- 3.8 x 10-6 A
- 1.0 x 10-5 A
- 2.5 x 10-3 A
- 3.8 x 10-2 A
- 1.0 x 10-1 A
- As shown in Fig. 5, a loop of wire moves through
successive regions of zero magnetic field, a magnetic field
of 1 Tesla into the page, a magnetic field of 1 Tesla out of
the page, and again zero magnetic field. What is the
direction of the induced current when the loop is at
(i) position A, (ii) position B, and (iii) position C?
- (i) clockwise (ii) clockwise (iii) counterclockwise
- (i) clockwise (ii) counterclockwise (iii) clockwise
- (i) counterclockwise (ii) clockwise (iii) clockwise
- (i) counterclockwise (ii) counterclockwise (iii) clockwise
- (i) counterclockwise (ii) clockwise (iii) counterclockwise
- In the above problem, if the loop is square piece of wire 2 cm on
a side with resistance of 200 Ohms,
and the loop is being pulled at a constant velocity of 5 m/s, what is
the magnitude of the force on the loop at position B due to the
magnetic field?
- 0 N
- 1 x 10-5 N
- 2 x 10-5 N
- 4 x 10-5 N
- 8 x 10-5 N
- A snapshot of a generator which is rotating counterclockwise
is shown in Fig. 6. Which direction is the current, I, flowing
(i) at this point in time and (ii) after the loop
rotates by 90 degrees counterclockwise?
- (i) from A to B (ii) from A to B
- (i) from A to B (ii) from B to A
- (i) from B to A (ii) from A to B
- (i) from B to A (ii) from B to A
- none of the above
- Place your name, social security number, and exam number on
your bubble sheet -- NOW. Also, print and sign your name on the
exam printout.
- Done correctly.
- Done incorrectly.
- Done incorrectly.
- Done incorrectly.
- Done incorrectly.
- A light pulse is sent around the equator in an optical fiber.
Assuming that the fiber is made of glass
with an index of refraction of 1.5 and that the radius of the earth
is 6.38 x 106 m, how long does it take the pulse to go once
around the earth?
- 0.03 sec
- 0.09 sec
- 0.13 sec
- 0.17 sec
- 0.20 sec
- As shown in Fig. 7, light polarized at 130 degrees with
intensity Io is incident
from the left and passes sequentially through polarizers at angles,
160, 0, and 50 degrees. What is the intensity of the light exiting on
the right?
- 0.07 Io
- 0.13 Io
- 0.15 Io
- 0.27 Io
- 0.36 Io
- In Fig. 8 light is incident from the left at 10 degrees relative to the
horizontal. What is the angle of the exiting
light relative to the horizontal?
- 6 degrees
- 12 degrees
- 18 degrees
- 24 degrees
- 30 degrees
- An object of height 1 cm is 5 cm from a spherical convex mirror.
If the image is virtual and 0.4 cm high, what is the radius of
curvature of the mirror?
- 1.4 cm
- 2.8 cm
- 3.3 cm
- 4.5 cm
- 6.7 cm
- An object is placed 18 cm in front of a converging lens with
focal length 36 cm. Which of the following correctly characterizes
the resulting image?
- real, upright, and larger than the object
- real, inverted, and larger than the object
- real, inverted, and smaller than the object
- virtual, upright, and larger than the object
- virtual, upright, and smaller than the object
- Draw a ray diagram to determine the
position of the image created by the converging lens
shown in Fig. 9.
- A
- B
- C
- D
- E
- Draw a ray diagram to determine the position of
the image created by the convex mirror shown in
Fig. 10.
- A
- B
- C
- D
- E
- Determine whether the image will become larger
or smaller when the object moves (i) closer to the
lens in Fig. 9 and (ii) closer to the mirror in Fig. 10.
- (i) smaller (ii) smaller
- (i) smaller (ii) larger
- (i) larger (ii) smaller
- (i) larger (ii) larger
- none of the above
- An object lies in one
of four regions next to the diverging lens
shown in Fig. 11.
List all the regions where the resulting image will be real.
(Note in this problem we are allowing for the the
object to be on the side of the outgoing light,
which can happen if there is another lens to the
left of the lens shown in the figure.)
- II
- III
- IV
- III and IV
- II, III, and IV
- Two lenses are placed on the x-axis. The first lens is a converging
lens with focal length 2 cm placed at x = -4 cm. The second lens
is a diverging lens with focal length 8 cm placed at x = 2 cm. If
an object is placed at x = -17 cm, what is the position of the image?
- x = -4.5 cm
- x = -3.5 cm
- x = -2.5 cm
- x = -1.5 cm
- x = -0.5 cm
- In the above problem, what is the overall magnification of the image?
- -0.33
- -0.12
- 0.12
- 0.21
- 0.33