PHY3054 - Exam 2 - Fall 95 - Selman Hershfield
1. Four wires are made of the same material with different lengths and thicknesses. Wire number 1 is 1m long and 1mm in diameter. Wire number 2 is 2m long and 2mm in diameter. Wire number 3 is 2m long and 1mm in diameter. Wire number 4 is 1m long and 0.5mm in diameter. Which wire(s) has the largest resistance?

1. Wire 1
2. Wire 2
3. Wire 3
4. Wire 4
5. Wires 3 and 4

2. What is the effective resistance of the resistors shown in Fig. 1?

1. 1 Ohm
2. 3 Ohms
3. 4.5 Ohms
4. 6 Ohms
5. 7.5 Ohms

3. In Fig. 2 what is the magnitude of the current flowing through the 1 Ohm resistor?

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

4. In Fig. 3 the resistors represent light bulbs which have identical resistances. Which light bulb(s) are the brightest?

1. A
2. B and C
3. D and E
4. A, B, and C
5. All are equal in brightness.

5. You are given a 1 Ohm, a 3 Ohm, and a 6 Ohm resistor. What is the smallest effective resistance one can obtain by combining these resistors in series, in parallel, or some mixture of series and parallel?

1. 0.17 Ohms
2. 0.67 Ohms
3. 1 Ohm
4. 1.5 Ohms
5. 10 Ohms

6. In Fig. 4 what is the current labelled I?

1. -50mA
2. 5mA
3. 10mA
4. 15mA
5. 50mA

7. What is the current labelled I1 in Fig. 5?

1. -0.45 A
2. -0.36 A
3. 0.09 A
4. 0.36 A
5. 0.45 A

8. What is the difference between the voltages, VA - VB, in Fig. 5?

1. -1.91 V
2. -1.64 V
3. -1.55 V
4. 1.55 V
5. 1.64 V

9. The circuit in Fig. 6 consists of two 1.5V batteries connected in series with a 100 Ohm resistor. The batteries each have an internal resistance of 10 Ohms. Which of the following is not true?

1. The 100 Ohm resistor dissipates energy at a rate of 62.5 mW.
2. Each battery dissipates 6.25 mW internally because of the internal resistance.
3. The net power supplied by each battery to the circuit is 31.25 mW.
4. The voltage across the each battery is 1.5V while the current is flowing.
5. All of these statements are true.

10. Figures 7.1 and 7.2 shows two possible connections of a meter in a simple circuit. (i) Which connection is correct for a voltmeter? (ii) Should a voltmeter have a large resistance or a small resistance?

1. (i) Fig. 7.1 (ii) small resistance
2. (i) Fig. 7.1 (ii) large resistance
3. (i) Fig. 7.2 (ii) small resistance
4. (i) Fig. 7.2 (ii) large resistance
5. (i) Either Figs. 7.1 or 7.2 (ii) small resistance

11. 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.

12. A uniform magnetic field goes from left to right as shown in Fig. 8. (i) What is the direction of the force on the wire shown in Fig. 8.1? (ii) What is the direction of the force on the electron in Fig. 8.2, which moves in the same direction as the magnetic field?

1. (i) into the page (ii) no force on the electron
2. (i) into the page (ii) out of the page
3. (i) out of the page (ii) into the page
4. (i) out of the page (ii) no force on the electron
5. (i) no force on the wire (ii) out of the page

13. Two compasses are placed next to a bar magnet as shown in Fig. 9. Which directions do the needles of (i) compass number one and (ii) compass number two point? (The needles point in the direction of the magnetic field.)

1. (i) north (ii) north
2. (i) north (ii) south
3. (i) south (ii) north
4. (i) south (ii) south
5. none of the above

14. A proton travels in a circle perpendicular to a magnetic field. If it completes an orbit in 1 millisecond, what it the magnitude of the magnetic field?

1. 0.1x10-4 Tesla
2. 0.33x10-4 Tesla
3. 0.66x10-4 Tesla
4. 1.0x10-4 Tesla
5. Not enough information given

15. A loop of wire has a current, I, flowing counterclockwise as shown in Fig. 10. Two smaller loops, labelled 1 and 2, are placed in the magnetic field produced by the larger loop. What directions should current flow in these loops to minimize their potential energy?

1. clockwise in loop 1 and clockwise in loop 2
2. clockwise in loop 1 and counterclockwise in loop 2
3. counterclockwise in loop 1 and clockwise in loop 2
4. counterclockwise in loop 1 and counterclockwise in loop 2
5. none of the above

16. What is the magnitude and direction of the magnetic field at point P in Fig. 11?

1. 0 Tesla
2. 4.3x10-7 Tesla into page
3. 4.3x10-7 Tesla out of page
4. 8.6x10-7 Tesla into page
5. 8.6x10-7 Tesla out of page

17. What is the magnitude and direction of the magnetic field at point P in Fig. 12?

1. 0.9x10-6 Tesla into the page
2. 0.9x10-6 Tesla out of the page
3. 1.1x10-6 Tesla into the page
4. 1.1x10-6 Tesla out of the page
5. 2x10-6 Tesla into the page

18. What is the net force per unit length on the wire carrying 2A in Fig. 13?

1. 8x10-7 N/m up
2. 8x10-7 N/m down
3. 16x10-7 N/m up
4. 16x10-7 N/m down
5. 24x10-7 N/m up

19. Two wires carrying 2 amperes of current each are placed in a uniform magnetic field. The wires make an angle of 40 degrees with each other. Neglecting the magnetic fields due to the wires, if there is no net force on one wire and the other wire experiences a force of 5 Newtons/meter, what is the magnitude of the external magnetic field?

1. 0.7 Tesla
2. 1.6 Tesla
3. 2.5 Tesla
4. 3.9 Tesla
5. Not enough information given.

20. What is the net force on the rectangular loop of wire in Fig. 14?

1. 2x10-7 N to the left
2. 2x10-7 N to the right
3. 4x10-7 N to the left
4. 4x10-7 N to the right
5. 0 N

1. Answer = (4) Wire 4
2. Answer = (1) 1 Ohm
3. Answer = (4) 0.8 A
4. Answer = (4) A, B, and C
5. Answer = (2) 0.67 Ohms
7. Answer = (1) -0.45 A
8. Answer = (2) -1.64 V
9. Answer = (4) The voltage across the each battery is 1.5V while the current is flowing.
10. Answer = (4) (i) Fig. 7.2 (ii) large resistance
11. Answer = (1) Done correctly.
12. Answer = (1) (i) into the page (ii) no force on the electron
13. Answer = (2) (i) north (ii) south
14. Answer = (3) 0.66x10-4 Tesla
15. Answer = (3) counterclockwise in loop 1 and clockwise in loop 2
16. Answer = (4) 8.6x10-7 Tesla into page
17. Answer = (2) 0.9x10-6 Tesla out of the page
18. Answer = (2) 8x10-7 N/m down
19. Answer = (4) 3.9 Tesla
20. Answer = (4) 4x10-7 N to the right