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.

1. 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. 1.2 x 10-5 N
2. 2.4 x 10-5 N
3. 3.6 x 10-5 N
4. 4.8 x 10-5 N
5. 7.2 x 10-5 N

2. 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?

1. 45 degrees
2. 90 degrees
3. 135 degrees
4. 225 degrees
5. 315 degrees

3. 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?

1. I only
2. II only
3. III only
4. I and III
5. I, II, and III

4. 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)?

1. (i) clockwise (ii) clockwise
2. (i) clockwise (ii) counterclockwise
3. (i) counterclockwise (ii) clockwise
4. (i) counterclockwise (ii) counterclockwise
5. none of the above

5. 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?

1. 3.8 x 10-6 A
2. 1.0 x 10-5 A
3. 2.5 x 10-3 A
4. 3.8 x 10-2 A
5. 1.0 x 10-1 A

6. 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?

1. (i) clockwise (ii) clockwise (iii) counterclockwise
2. (i) clockwise (ii) counterclockwise (iii) clockwise
3. (i) counterclockwise (ii) clockwise (iii) clockwise
4. (i) counterclockwise (ii) counterclockwise (iii) clockwise
5. (i) counterclockwise (ii) clockwise (iii) counterclockwise

7. 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?

1. 0 N
2. 1 x 10-5 N
3. 2 x 10-5 N
4. 4 x 10-5 N
5. 8 x 10-5 N

8. 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?

1. (i) from A to B (ii) from A to B
2. (i) from A to B (ii) from B to A
3. (i) from B to A (ii) from A to B
4. (i) from B to A (ii) from B to A
5. none of the above

9. Place your name, social security number, and exam number on your bubble sheet -- NOW. Also, print and sign your name on the exam printout.

1. Done correctly.
2. Done incorrectly.
3. Done incorrectly.
4. Done incorrectly.
5. Done incorrectly.

10. 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?

1. 0.03 sec
2. 0.09 sec
3. 0.13 sec
4. 0.17 sec
5. 0.20 sec

11. 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?

1. 0.07 Io
2. 0.13 Io
3. 0.15 Io
4. 0.27 Io
5. 0.36 Io

12. 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?

1. 6 degrees
2. 12 degrees
3. 18 degrees
4. 24 degrees
5. 30 degrees

13. 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. 1.4 cm
2. 2.8 cm
3. 3.3 cm
4. 4.5 cm
5. 6.7 cm

14. 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?

1. real, upright, and larger than the object
2. real, inverted, and larger than the object
3. real, inverted, and smaller than the object
4. virtual, upright, and larger than the object
5. virtual, upright, and smaller than the object

15. Draw a ray diagram to determine the position of the image created by the converging lens shown in Fig. 9.

1. A
2. B
3. C
4. D
5. E

16. Draw a ray diagram to determine the position of the image created by the convex mirror shown in Fig. 10.

1. A
2. B
3. C
4. D
5. E

17. 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.

1. (i) smaller (ii) smaller
2. (i) smaller (ii) larger
3. (i) larger (ii) smaller
4. (i) larger (ii) larger
5. none of the above

18. 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.)

1. II
2. III
3. IV
4. III and IV
5. II, III, and IV

19. 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?

1. x = -4.5 cm
2. x = -3.5 cm
3. x = -2.5 cm
4. x = -1.5 cm
5. x = -0.5 cm

20. In the above problem, what is the overall magnification of the image?

1. -0.33
2. -0.12
3. 0.12
4. 0.21
5. 0.33