PHY3054 - Final - Fall 1995 - Selman Hershfield
  1. Three charges are arranged in an equilateral triangle as shown in Fig. 1. What is the direction of the force on the +1 micro-Coulomb charge? (Hint: draw a vector diagram.)

    1. -150 degrees
    2. -30 degrees
    3. 30 degrees
    4. 120 degrees
    5. 150 degrees

  2. What is the magnitude of the force on the +1 micro-Coulomb charge in Fig. 1?

    1. 0.5 N
    2. 0.9 N
    3. 1.6 N
    4. 2.1 N
    5. 2.7 N

  3. Two large charged parallel plates produce electric fields E1 and E2 as shown in Fig. 2. The magnitude of E1 is 1 x 106 V/m, and the magnitude of E2 is 2 x 106 V/m. What is the charge density for the right plate?

    1. -26.55 x 10-6 C/m2
    2. -8.85 x 10-6 C/m2
    3. 8.85 x 10-6 C/m2
    4. 17.7 x 106 C/m2
    5. 26.55 x 10-6 C/m2

  4. In Fig. 3 a ball is suspended in a uniform electric field of magnitude 2 x 104 V/m. If the mass of the ball is 25g, and the charge on the ball is 3 micro-Coulomb, what is the angle X? (Assume gravity acts downward; g = 9.8 x m/s2)

    1. 0 degrees
    2. 14 degrees
    3. 22 degrees
    4. 34 degrees
    5. 76 degrees

  5. The electrical potential at a distance R from a point charge is 1V. What is the electrical potential at 2R?

    1. 0.25V
    2. 0.5V
    3. 1V
    4. 2V
    5. 4V

  6. In Fig. 4 a +3 micro-Coulomb charge and a -2 micro-Coulomb charge are placed on the x-axis. In which of the regions on the x-axis is there a point where the electrical potential is zero?

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

  7. If the charge on the 1 micro-Farad capacitor in Fig. 5 is 2 micro-Coulomb, what is the charge on the 2 micro-Farad capacitor?

    1. 0.5 micro-Coulomb
    2. 1.0 micro-Coulomb
    3. 1.5 micro-Coulomb
    4. 2.0 micro-Coulomb
    5. 8.0 micro-Coulomb

  8. Which of the capacitors in Fig. 6 have the largest voltage? Assume that they all have the same capacitance.

    1. A
    2. B and C
    3. D and E
    4. A, B, and C
    5. All have the same voltage.

  9. What is the effective resistance of the circuit shown in Fig. 7? All resistors are 1 Ohm.

    1. 0.2 Ohms
    2. 0.4 Ohms
    3. 0.6 Ohms
    4. 0.8 Ohms
    5. 1.0 Ohms

  10. All the resistors in Fig. 8 have the same value. How does the current labeled I change when the switch is closed?

    1. I goes up by a factor of 3.
    2. I goes up by a factor of 2.
    3. I remains the same.
    4. I goes down by a factor of 2.
    5. I goes down by a factor of 3.

  11. What is R in Fig. 9 in order for the current through the 3 Ohm resistor to be zero?

    1. 0.33 Ohm
    2. 0.67 Ohm
    3. 1 Ohm
    4. 1.33 Ohm
    5. 2 Ohm

  12. A magnetic field goes into the plane of the page. Three particles with charges Q1, Q2, and Q3 travel in the plane of the page. Particle Q1 rotates counterclockwise in a circle, particle Q2 goes in a straight line, and particle Q3 rotates clockwise in a circle. What are the signs of Q1, Q2, and Q3?

    1. Q1 > 0, Q2 = 0, and Q3 < 0
    2. Q1 > 0, Q2 < 0, and Q3 = 0
    3. Q1 = 0, Q2 > 0, and Q3 < 0
    4. Q1 < 0, Q2 > 0, and Q3 = 0
    5. Q1 < 0, Q2 = 0, and Q3 > 0

  13. As shown in Fig. 10 an electron travels parallel to a wire carrying current 5A. If the velocity of the electron is 3 x 105 m/s and it is 2 x 10-6 m from the wire, what is the force on the electron?

    1. 2.4 x 10-14 N up
    2. 2.4 x 10-14 N down
    3. 7.5 x 10-14 N up
    4. 7.5 x 10-14 N down
    5. 0 N

  14. What is the magnetic field at point P in Fig. 11?

    1. 0 T
    2. 6 x 10-7 T out of the page
    3. 6 x 10-7 into the page
    4. 10 x 10-7 out of the page
    5. 10 x 10-7 into the page

  15. In Fig. 12 six wires carry current of equal magnitude perpendicular to the plane of the page. As marked in the figure the direction of the current flow is either into or out of the page. What is the direction of the magnetic field at the center of the hexagon?

    1. 30 degrees
    2. 90 degrees
    3. 150 degrees
    4. 210 degrees
    5. 270 degrees

  16. A square loop of wire 1cm on a side with resistance 4 Ohms travels from a region where the magnetic field is 3T to a region where the magnetic field is 1T (see Fig. 13). If the velocity of the loop is 5m/s, what is the induced current in the loop?

    1. 25mA clockwise
    2. 25mA counterclockwise
    3. 37.5mA clockwise
    4. 50mA clockwise
    5. 50mA counterclockwise

  17. What is the direction of the induced current in the circular loop in Fig. 14 right after the switch is closed?

    1. Clockwise
    2. Counterclockwise
    3. Blank
    4. Blank
    5. Blank

  18. If the distance to the sun is 1.5 x 1011 m, how long does it take light to reach the earth from the sun?

    1. 0.002 sec
    2. 0.5 sec
    3. 4.5 sec
    4. 20 sec
    5. 500 sec

  19. Light travels through the corner of a piece of a glass with index of refraction 1.5 (see Fig. 15). What is the angle X of the transmitted light?

    1. 7 degrees
    2. 10 degrees
    3. 13 degrees
    4. 20 degrees
    5. No light is transmitted.

  20. Three polarizers are arranged in series as shown in Fig. 16. If unpolarized light is incident from the left, what are all the possible orientations for the right most polarizer so that no light gets through on the right?

    1. 22.5 degrees
    2. 90 degrees
    3. 135 degrees
    4. 90 and 135 degrees
    5. 22.5, 90, and 135 degrees

  21. In Fig. 17 an object is placed to the left of glass hemisphere with radius 1m and index of refraction 1.5. Where is the image of this object?

    1. 2m
    2. 4m
    3. 6m
    4. 8m
    5. Infinity

  22. A swimming pool is 3m deep. A mirror is placed at the bottom of the pool. If a fish swims 1m from the bottom of the pool, how far below the surface of the water does the fish's reflection in the mirror appear to be to an observer outside the water? Assume the index of refraction of the water is 1.33.

    1. 1.5 m
    2. 2 m
    3. 2.25 m
    4. 3 m
    5. 5.3 m

  23. What is the position of the image due to the diverging lens in Fig. 18? The focal point is labeled by F. (Draw a ray diagram.)

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

  24. What is the position of the image due to the concave mirror in Fig. 19? The focal point is labeled by F, and the center is labeled by R. (Draw a ray diagram.)

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


Answers
  1. Answer = (5) 150 degrees
  2. Answer = (3) 1.6 N
  3. Answer = (2) -8.85 x 10-6 C/m2
  4. Answer = (2) 14 degrees
  5. Answer = (2) 0.5V
  6. Answer = (5) Regions II and III
  7. Answer = (1) 0.5 micro-Coulomb
  8. Answer = (4) A, B, and C
  9. Answer = (3) 0.6 Ohms
  10. Answer = (1) I goes up by a factor of 3.
  11. Answer = (4) 1.33 Ohm
  12. Answer = (1) Q1 > 0, Q2 = 0, and Q3 < 0
  13. Answer = (2) 2.4 x 10-14 N down
  14. Answer = (2) 6 x 10-7 T out of the page
  15. Answer = (4) 210 degrees
  16. Answer = (1) 25mA clockwise
  17. Answer = (2) Counterclockwise
  18. Answer = (5) 500 sec
  19. Answer = (5) No light is transmitted.
  20. Answer = (3) 135 degrees
  21. Answer = (4) 8m
  22. Answer = (4) 3 m
  23. Answer = (1) A
  24. Answer = (3) C