PHY3054 - Final Exam - Fall 1996 - Selman Hershfield
1. 2 charges are arranged on an equilateral triangle as shown in Fig. 1. What is the direction of the electric field at P3 ?

1. 16 degrees
2. 134 degrees
3. 150 degrees
4. 164 degrees
5. 344 degrees

2. If a 3 micro-coulomb charge is placed at P3 in Fig. 1, what is the magnitude of the force on that charge?

1. 72 N
2. 89 N
3. 96 N
4. 105 N
5. 118 N

3. 3 charges are arranged on a rectangle as shown in Fig. 2. What is the electrical potential (voltage) at point P2 ?

1. 9x105 V
2. 14x105 V
3. 22x105 V
4. 36x105 V
5. 41x105 V

4. A -2 micro-Coulomb charge is placed at point P2 in Fig. 2. What is the potential energy of the entire charge configuration? (Assume that the potential energy is zero when the charges are infinitely far apart.)

1. -17 J
2. -23 J
3. -27 J
4. 11 J
5. 37 J

5. Two conducting shells surround a conducting sphere as shown in Fig. 3. If the net charge on the sphere is -1 micro-C, the net charge on the inner shell is 2 micro-C, and the electric field at point P is 1000 V/m pointing radially inwards, what is the net charge on the outer shell?

1. -2 micro-C
2. -1 micro-C
3. 0 micro-C
4. 1 micro-C
5. 2 micro-C

6. In the circuit shown in Fig. 4 each of the resistors are light bulbs with identical resistance. List the light bulbs from dimmest to brightest.

1. dimmest (AC),(DEF),(B) brightest
2. dimmest (C),(AB),(DEF) brightest
3. dimmest (C),(B),(DEF),(A) brightest
4. dimmest (C),(DEF),(AB) brightest
5. dimmest (C),(DEF),(B),(A) brightest

7. In Fig. 4, what is the voltage difference, VP1 - VP2 ?

1. -6 V
2. -3 V
3. -1.5 V
4. 1.5 V
5. 3 V

8. In Fig. 5, if the current through the whole network is 3 A, what is the voltage across R2 ?

1. 6 V
2. 7 V
3. 9 V
4. 11 V
5. 18 V

9. In Fig. 6, if the energy stored in C3 is 0.5 micro-J, what is the energy stored in C5 ? (Choose the closest answer.)

1. 0.05 micro-J
2. 0.5 micro-J
3. 5 micro-J
4. 50 micro-J
5. 500 micro-J

10. What is the current labeled I in Fig. 7?

1. -1.5 A
2. -0.75 A
3. 0 A
4. +0.75 A
5. +1.5 A

11. A wire carries current from left to right as shown in Fig. 8. What is the direction of the force on (i) an electron moving towards the wire (Fig. 8.1) and (ii) a proton moving parallel to the wire (Fig. 8.2). Assume that both the electron and the proton move in the plane of the paper. Use the direction conventions shown on the figure sheet.

1. (i) 0 degrees and (ii) 90 degrees
2. (i) 0 degrees and (ii) 270 degrees
3. (i) 90 degrees and (ii) 90 degrees
4. (i) 180 degrees and (ii) 90 degrees
5. (i) 180 degrees and (ii) 270 degrees

12. Two wires carry currents of 2A and 1A as shown in Fig. 9. In which of the three regions (I, II, and III) can the magnetic field be equal to zero?

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

13. Three wires carrying current perpendicular to the plane of the page are situated at the corners of an equilateral triangle as shown in Fig. 10. If the magnitude of the current in each wire is the same, what is the direction of the magnetic field at the center of the triangle?

1. 60 degrees
2. 120 degrees
3. 210 degrees
4. 240 degrees
5. 330 degrees

14. A square loop moves through a region of magnetic field coming out of the plane of the page as shown in Fig. 11. Which of the graphs in Fig. 11 correspond to the force on the loop and the direction of the induced current? Assume that the force is positive to the right and clockwise is positive for the induced current.

1. Fig. 11.1 is the force, and Fig. 11.3 is the current.
2. Fig. 11.1 is the force, and Fig. 11.4 is the current.
3. Fig. 11.2 is the force, and Fig. 11.3 is the current.
4. Fig. 11.2 is the force, and Fig. 11.4 is the current.
5. None of the above.

15. The motor shown in Fig. 12.1 is rotating clockwise. (i) What is the direction of the current flow at point P? The DC generator shown in Fig. 12.2 is also rotating clockwise. (ii) What is the direction of the current flow at point Q?

1. (i) to the right and (ii) to the right
2. (i) to the left and (ii) to the right
3. (i) to the right and (ii) to the left
4. (i) to the left and (ii) to the left
5. none of the above

16. Light is incident from the left at 14 degrees relative to the horizontal in Fig. 13. What is the angle of exiting light relative to the horizontal? (Choose the closest answer.)

1. 11 degrees
2. 12 degrees
3. 13 degrees
4. 14 degrees
5. 15 degrees

17. Two polarizers are placed in between a pair of crossed polarizers (see Fig. 14). How many ways can the middle polarizers be rotated so that no light gets through all four polarizers? (Assume that rotating a polarizer by 180 degrees gives the same result.)

1. 1
2. 2
3. 4
4. 8
5. infinite

18. An object is placed at x = -17 cm, lens A is placed at x = -5 cm, and lens B is placed at x = 5 cm. Are the following statements true or false? (i) If lens A is converging and lens B is diverging, the final image MUST BE virtual. (ii) If lens A is diverging and lens B is converging, the image CAN NOT be virtual.

1. (i) True and (ii) True
2. (i) True and (ii) False
3. (i) False and (ii) True
4. (i) False and (ii) False
5. Blank

19. Two lenses are placed on the x-axis. The first lens is a diverging lens with focal length 10 cm placed at x = -7 cm. The second lens is a diverging lens with focal length 12 cm placed at x = 6 cm. If an object is placed at x = -19 cm, what is the image position? (Choose the closest answer.)

1. -2.5 cm
2. -1.25 cm
3. -0.75 cm
4. 0 cm
5. 1.5 cm

20. Put your name, social security number, and test number correctly on the bubble sheet and the exam printout.

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

1. Answer = (5) 344 degrees
2. Answer = (4) 105 N
3. Answer = (2) 14x105 V
4. Answer = (3) -27 J
5. Answer = (1) -2 micro-C
6. Answer = (5) dimmest (C),(DEF),(B),(A) brightest
7. Answer = (3) -1.5 V
8. Answer = (1) 6 V
9. Answer = (3) 5 micro-J
10. Answer = (1) -1.5 A
11. Answer = (2) (i) 0 degrees and (ii) 270 degrees
12. Answer = (1) I only
13. Answer = (5) 330 degrees
14. Answer = (4) Fig. 11.2 is the force, and Fig. 11.4 is the current.
15. Answer = (2) (i) to the left and (ii) to the right
16. Answer = (2) 12 degrees