PHY3054 - Final - Fall 1994 - Selman Hershfield
1. Three charges are arranged on the corners of a square as shown in Figure 1. What is the magnitude of the force on the charge Q1?

1. 4.5 x 109 N
2. 6.5 x 109 N
3. 9 x 109 N
4. 11.5 x 109 N
5. 13.5 x 109 N

2. Three charges are arranged on the corners of a square as shown in Figure 1. What is the direction of the force on the charge Q1?

1. -60 degrees
2. -30 degrees
3. 0 degrees
4. 30 degrees
5. 60 degrees

3. A conducting sphere is enclosed by two different conducting shells as shown in Fig. 2. The charge on the sphere is 1C, the charge on the inner shell is -2C, and the charge on the outer shell is 3C. What is the net charge on the inside surface of the outer shell?

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

4. (Qualitative) Six charges are arranged on the corners of a hexagon as shown in Figure 3. Which of the following is true of the electric field, E, and the electrical potential, V, at the center of the hexagon?

1. V is zero, and E is zero.
2. V is not zero, and E is zero.
3. V is zero, and E is not zero.
4. V is not zero, and E is not zero.
5. Not enough information is given.

5. What is the potential energy of the charge configuration shown in Figure 1? (Assume that the potential energy is zero when the charges are infinitely far apart.)

1. -5.4 x 1010 J
2. -2.3 x 1010 J
3. -1.8 x 1010 J
4. 1.8 x 1010 J
5. 4.9x1010 J

6. An electron is released from rest 1 mm from a point charge of 10-15C. The point charge is not allowed to move. What is the distance of the electron from the point charge when the electron's velocity is 105 m/s?

1. 0.24 mm
2. 0.32 mm
3. 0.46 mm
4. 0.58 mm
5. 0.75 mm

7. (Qualitative) Which of the following is not true?

1. Two capacitors in series have the same charge.
2. The net voltage drop around a closed loop is zero.
3. Two resistors in parallel have the same voltage drop.
4. Capacitors store charge.
5. Resistors store energy.

8. In Figure 4 all capacitors have capacitance 1 micro-Farad. If the charge on the left most capacitor is 1 micro-Coulomb, what is the charge on the right most capacitor?

1. 0.2 micro-Coulomb
2. 0.4 micro-Coulomb
3. 1 micro-Coulomb
4. 2 micro-Coulomb
5. 4 micro-Coulomb

9. (Qualitative) Which of the circuits in Fig. 5 are different?

1. Figure 5.1
2. Figure 5.2
3. Figure 5.3
4. Figure 5.4
5. Figure 5.5

10. Using Kirchoff's point rule determine the current labelled I in Figure 6.

1. I = 1 A
2. I = 2 A
3. I = 3 A
4. I = 4 A
5. I = 5 A

11. What is the resistance of the circuit shown in Figure 7?

1. 1.5 Ohms
2. 2.3 Ohms
3. 4.7 Ohms
4. 6 Ohms
5. 9.5 Ohms

12. (Qualitative) For a uniform magnetic field coming out of the plane of the page what is (i) the direction of circular motion of an electron and (ii) the direction of the force on a wire with current moving from left to right? Assume that both the particle and the wire are in the plane of the page.

1. (i) Clockwise, (ii) towards the top of the page.
2. (i) Clockwise, (ii) towards the bottom of the page.
3. (i) Counter-clockwise, (ii) towards the top of the page.
4. (i) Counter-clockwise, (ii) towards the bottom of the page.
5. None of the above.

13. An electron moves in a circle perpendicular to a magnetic field. If the time it takes the electron to complete one revolution is 10-11 seconds, what is the magnitude of the magnetic field?

1. 0.6 Tesla
2. 1.8 Tesla
3. 2.4 Tesla
4. 3.6 Tesla
5. Not enough information given.

14. (Qualitative) If all three wires in Figure 8 carry the same current, what is the direction of the force on the top, middle, and bottom wires, respectively.

1. top: up; middle: down; bottom: up.
2. top: up; middle: down; bottom: down.
3. top: down; middle: up; bottom: up.
4. top: down; middle: up; bottom: down.
5. None of these.

15. Four wires carrying current I = 2 A are arranged as shown in Figure 9. What is the magnitude and direction of the magnetic field at point P?

1. 0 Tesla
2. 0.75 x 10-6 Tesla out of the page
3. 0.75 x 10-6 Tesla into the page
4. 1 x 10-6 Tesla out of the page
5. 1 x 10-6 Tesla into the page

16. A square loop of side 5 cm is pulled from a region of magnetic field B = 2 Tesla out of the page to region of zero magnetic field (see Fig. 10). If the loop has resistance 25 Ohms and velocity 1 m/s, what is the magnitude and direction of the induced current?

1. 0 mA
2. 0.8 mA Clockwise
3. 0.8 mA Counter-clockwise
4. 4 mA Clockwise
5. 4 mA Counter-clockwise

17. (Qualitative) In Figure 11.1 the current, I1, increases. What is the direction of the induced current in the inner loop? In Figure 11.2 the current, I2, decreases. What is the direction of the induced current in the other loop?

1. Clockwise in Fig. 11.1 and clockwise in Fig. 11.2.
2. Clockwise in Fig. 11.1 and counterclockwise in Fig. 11.2.
3. Counterclockwise in Fig. 11.1 and clockwise in Fig. 11.2.
4. Counterclockwise in Fig. 11.1 and counterclockwise in Fig. 11.2.
5. None of the above.

18. (Qualitative) Which of the following is not an electromagnetic wave?

1. Sound waves
2. X-rays
3. Microwaves
4. Ultraviolet light

19. A light ray traveling in a vacuum hits the surface of a material with refractive index n1 greater than unity. It continues until it hits another surface which has a refractive index n2 greater than unity (see Figure 13). Is it possible for the light ray to be totally internally reflected at the second surface?

1. Yes
2. No
3. Blank
4. Blank
5. Blank

20. (Qualitative) You are given 4 polarizers, which are to be arranged in series. If unpolarized light of incoming intensity I0 is shined on the polarizers, what is the maximum possible intensity of the light emerging after passing through all four polarizers?

1. 0
2. I0 /16
3. I0 /4
4. I0 /2
5. I0

21. A concave mirror has radius 9 cm. The image of an object in the mirror is 2.5 times the size of the object and inverted. What is the distance of the object from the mirror?

1. 6.3 cm
2. 12.6 cm
3. 15.75 cm
4. 20.4 cm
5. 31.5 cm

22. (Qualitative) Which of the principle rays for the convex mirror in Figure 12 is incorrect?

1. Ray 1
2. Ray 2
3. Ray 3
4. Ray 4
5. All the rays are correct.

23. (Qualitative) True or False: A converging lens always produces a real image, and a diverging lens always produces a virtual image.

1. True
2. False
3. Blank
4. Blank
5. Blank

24. Two lenses with focal lengths 1 cm and 9 cm are separated by 10 cm. An object is 2 cm from the lens with the 1 cm focal length as shown in Fig. 14. What is the position of the final image in the coordinate system of Fig. 14?

1. -72 cm
2. -8 cm
3. -2.6 cm
4. 1.6 cm
5. 4.2 cm

1. Answer = (2) 6.5 x 109 N
2. Answer = (1) -60 degrees
3. Answer = (4) +1 C
4. Answer = (2) V is not zero, and E is zero.
5. Answer = (2) -2.3 x 1010 J
6. Answer = (1) 0.24 mm
7. Answer = (5) Resistors store energy.
8. Answer = (1) 0.2 micro-Coulomb
9. Answer = (4) Figure 5.4
10. Answer = (2) I = 2 A
11. Answer = (1) 1.5 Ohms
12. Answer = (4) (i) Counter-clockwise, (ii) towards the bottom of the page.
13. Answer = (4) 3.6 Tesla
14. Answer = (4) top: down; middle: up; bottom: down.
15. Answer = (5) 1 x 10-6 Tesla into the page
16. Answer = (5) 4 mA Counter-clockwise
17. Answer = (1) Clockwise in Fig. 11.1 and clockwise in Fig. 11.2.
18. Answer = (1) Sound waves