PHY2054 - Exam 2 - Fall 1997 - Selman Hershfield
1. In Fig. 1 each of the resistors are light bulbs with identical resistance. List the light bulbs from the dimmest to the brightest. Group light bulbs with the same brightness in parentheses.

1. dimmest (ABDE),(CF) brightest
2. dimmest (CF),(ABDE) brightest
3. dimmest (DE),(AB),(CF) brightest
4. dimmest (DE),(ABCF) brightest
5. dimmest (DE),(CF),(AB) brightest

2. In Fig. 1 what is the voltage difference between points P1 and P2, VP1 - VP2 ? Assume that the resistors all have the same resistance.

1. -6 V
2. -3 V
3. 0 V
4. 3 V
5. 6 V

3. What is the effective resistance of the circuit shown in Fig. 2? (Choose the closest answer.)

1. 0.6 Ohms
2. 1.6 Ohms
3. 2.4 Ohms
4. 12 Ohms
5. 16 Ohms

4. In Fig. 3, if the voltage across R2 is 2V, what is the current through R3 ? (Choose the closest answer.)

1. 0.1 A
2. 0.3 A
3. 0.5 A
4. 0.7 A
5. 1.0 A

5. What is the current in the circuit shown in Fig. 4? Give both the magnitude and the direction. (Choose the closest answer.)

1. 0.5 A clockwise
2. 0.5 A counterclockwise
3. 0.6 A counterclockwise
4. 0.7 A clockwise
5. 0.7 A counterclockwise

6. What is the current going from B to E in Fig. 5?

1. -3 A
2. -1 A
3. 0 A
4. 1 A
5. 3 A

7. What is the voltage difference VC - VF in Fig. 5?

1. -8 V
2. -6 V
3. -2 V
4. 2 V
5. 8 V

8. What is the effective capacitance of the circuit shown in Fig. 6? (Choose the closest answer.)

1. 3.4 micro-F
2. 4.8 micro-F
3. 6.7 micro-F
4. 11.1 micro-F
5. 13.9 micro-F

9. In Fig. 7, if the voltage across C2 is 3V, what is the voltage across C4 ? (Choose the closest answer.)

1. 1.3 V
2. 2.4 V
3. 2.7 V
4. 3.0 V
5. 3.5 V

10. An RC circuit is shown in Fig. 8. What is the current through R1 (i) immediately after the switch is closed and (ii) infinitely long after the switch is closed?

1. (i) 0mA, (ii) 2mA
2. (i) 1mA, (ii) 2mA
3. (i) 1mA, (ii) 0mA
4. (i) 2mA, (ii) 0mA
5. (i) 2mA, (ii) 1mA

11. A voltmeter is attached across a resistor as shown in Fig. 9. If the voltage measured is 3.75 V, what is the internal resistance of the voltmeter?

1. 10 kilo-Ohms
2. 25 kilo-Ohms
3. 50 kilo-Ohms
4. 75 kilo-Ohms
5. 100 kilo-Ohms

12. Two charged particles, A and B, are injected into a mass spectrometer through the same electrical potential. The paths of the particles are shown in Fig. 10. Assuming that they have the same charge, what is the ratio of their masses: mA / mB ?

1. 0.25
2. 0.5
3. 1.4
4. 2
5. 4

13. Current carrying wires are placed in uniform magnetic fields as indicated in Figs. 11 (a) and (b). What is the direction of the force on the wires in both cases?

1. (a) into the page, (b) towards the top of the page
2. (a) into the page, (b) towards the bottom of the page
3. (a) out of the page, (b) towards the top of the page
4. (a) out of the page, (b) towards the bottom of the page
5. None of the above

14. A current carrying loop is placed in the y-z plane as shown in Fig. 12. What direction of an applied magnetic field would (i) minimize the potential energy and (ii) maximize the torque?

1. (i) x, (ii) y
2. (i) x, (ii) -z
3. (i) -x, (ii) -x
4. (i) -x, (ii) -z
5. (i) y, (ii) x

15. Two current carrying wires with currents IA and IB respectively are placed next to a bar magnet as shown in Fig. 13. What is the direction of the force, F, on each wire?

1. FA is towards the top of the page and FB is to the right.
2. FA is into the page and FB is zero.
3. FA is out of the page and FB is zero.
4. FA is into the page and FB is to the right.
5. FA is out of the page and FB is to the right.

16. A current carrying wire is placed in the x-y plane as shown in Fig. 14. The magnetic field is in the y-direction. If the force on the wire in Fig. 14 is 2N, what would be the force on the same wire if it is moved so that it makes an angle of 15 degrees with the x-axis? Hint: be careful to use the correct angles.

1. 1.04 N
2. 1.73 N
3. 2.23 N
4. 3.03 N
5. 3.86 N

17. A proton travels perpendicular to a uniform magnetic field. What is the magnitude of the applied magnetic field, if its direction of motion changes by 5 degrees in 10-9 seconds? (Choose the closest answer.)

1. 0.01 Tesla
2. 0.1 Tesla
3. 1 Tesla
4. 10 Tesla
5. 100 Tesla

18. Which of the following is NOT true of charged particles moving in a uniform magnetic field?

1. They always move in circles.
2. They have a constant speed.
3. The field does not do work on them.
4. The force is always perpendicular to the velocity.
5. They can not have a constant velocity.

19. An electric motor is shown in Fig. 15. (i) Which way must the current in the loop be flowing in order for the motor to be rotating counterclockwise? (ii) What is the direction of the magnetic moment of the loop when the motor is rotating counterclockwise?

1. (i) Clockwise, (ii) Down
2. (i) Clockwise, (ii) Up
3. (i) Clockwise, (ii) Right
4. (i) Counterclockwise, (ii) Down
5. (i) Counterclockwise, (ii) Up

20. 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.