106 practice exam 1 - byu physics and astronomy · physics 106 practice exam 1 there are 25...

Physics 106 Practice Exam 1 There are 25 questions, worth 4 points each. Your exam will have 20 questions. 1. Of the following substances, which one contains the highest density of free

electrons? a. hard rubber b. iron c. amber d. glass

2. If body M, with a positive charge, is used to charge body N by induction, what

will be the nature of the charge left on the latter? a. must be equal in magnitude to that on M b. must be negative c. must be positive d. must be greater in magnitude than that on M

3. Two point charges, separated by 1.5 cm, have charge values of +2.0 and −4.0

µC, respectively. What is the value of the mutual force between them? a. 320 N b. 3.6 × 10−8 N c. 8.0 × 10−12 N d. 3.1 × 10−3 N

4. An uncharged conductor is supported by an insulating stand. I pass a

positively charged rod near the left end of the conductor, but do not touch it. The right end of the conductor will be:

a. negative. b. positive. c. neutral. d. attracted.

5. In a thundercloud there may be an electric charge of +40 C near the top of the cloud and −40 C near the bottom of the cloud. These charges are separated by about 2.0 km. What is the electric force between these two sets of charges?

a. 3.6 × 104 N b. 3.6 × 105 N c. 3.6 × 106 N d. 3.6 × 107 N

6. Two identical spheres each carry a charge of −40.0 µC. The spheres are

separated by a distance of 1.00 m. What is the electric force between the spheres?

a. 28.8 N (repulsive) b. 14.4 N (repulsive) c. 7.19 N (attractive) d. 43.2 N (attractive)

7. A uniform electric field, with a magnitude of 600 N/C, is directed parallel to the positive x-axis. If the potential at x = 3.0 m is 1 000 V, what is the change in potential energy of a proton as it moves from x = 3.0 m to x = 1.0 m?

a. 8.0 × 10−17 J b. 1.9 × 10−16 J c. 0.80 × 10−21 J d. 500 J

8. An electron is released from rest at the negative plate of a parallel-plate

capacitor. If the distance across the plate is 5.0 mm and the potential difference across the plate is 5.0 V, with what velocity does the electron hit the positive plate? (me = 9.1 × 10−31 kg,)

a. 2.6 × 105 m/s b. 5.3 × 106 m/s c. 1.0 × 106 m/s d. 1.3 × 106 m/s

9. Two point charges of values +3.4 and +6.6 µC, respectively, are separated by

0.20 m. What is the potential energy of this 2-charge system?

a. +0.34 J b. −0.75 J c. +1.0 J d. −3.4 J

10. A point charge of +3.0 µC is located at the origin of a coordinate system and a

second point charge of −6.0 µC is at x = 1.0 m. At what point on the x axis is the electrical potential zero?

a. −0.25 m b. +0.25 m c. +0.33 m d. +0.75 m

11. What is the equivalent capacitance between points a and b? All capacitors are

1.0 µF.

a. 4.0 µF b. 1 7 µF c. 0.60 µF d. 0.25 µF

a b

12. A 10.0-µF capacitor is attached to a 20-V power supply. How much energy is

stored in the capacitor?

a. 2.0 × 10−3 J b. 1.2 × 10−3 J c. 2.0 × 10−4 J d. 5.2 × 10−4 J

13. A wire carries a steady current of 0.1 A over a period of 20 s. What total

charge passes through the wire in this time interval?

a. 200 C b. 20 C

c. 2 C d. 0.005 C

14. When you flip a switch to turn on a light, the delay before the light turns on is

determined by:

a. the number of electron collisions per second in the wire. b. the drift speed of the electrons in the wire. c. the speed of the electric field moving in the wire. d. none of these, since the light comes on instantly.

15. If a 500-W heater carries a current of 4.00 A, what is the resistance of the

heating element?

a. 85.7 Ω b. 42.8 Ω c. 31.3 Ω d. 11.2 Ω

16. A light bulb has resistance of 240 Ω when operating at 120 V. Find the current in the light bulb.

a. 2.0 A b. 1.0 A c. 0.50 A d. 0.20 A

17. A high-voltage transmission line carries 1 000 A at 700 000 V. What is the

power carried by the line? a. 700 MW b. 370 MW c. 100 MW d. 70 MW

18. A 500-W heater carries a current of 4.0 A. How much does it cost to operate

the heater for 30 min if electrical energy costs 6.0 cents per kWh?

a. 1.5 cents

b. 9.0 cents c. 18 cents d. 36 cents

19. The two ends of a 3.0-Ω resistor are connected to a 9.0-V battery. What is the

current through the resistor?

a. 27 A b. 6.3 A c. 3.0 A d. 0.33 A

20. When a 24.0-Ω resistor is connected across a 12.0-V battery, a current of 482 mA flows. What is the power output delivered by the emf of the battery?

a. 0.21 W b. 5.57 W c. 5.78 W d. 6.00 W 21. When a light bulb is turned on, its resistance increases until it reaches

operating temperature. What happens to the current in the bulb as it is warming up?

a. It stays constant. b. It increases. c. It decreases. d. It increases at first and then decreases. 22. Three resistors, with values of 2.0, 4.0 and 8.0 Ω, respectively, are connected

in parallel. What is the overall resistance of this combination? a. 0.58 Ω b. 1.1 Ω c. 7.0 Ω d. 14.0 Ω

23. Two resistors of values 6.0 and 12.0 Ω are connected in parallel. This combination in turn is hooked in series with a 2.0-Ω resistor and a 24-V battery. What is the current in the 2-Ω resistor?

a. 2.0 A b. 4.0 A c. 6.0 A d. 12 A

24. What is the current flowing

through the 2-Ω resistor? a. 2 A

b. 3 A c. 4 A d. 6 A 8 Ω

2 Ω

16 V

8 V

25. A 10-V-emf battery is

connected in series with the following: a 2-µF capacitor, a 2-Ω resistor, an ammeter, and a switch, initially open; a voltmeter is connected in parallel across the capacitor. After the switch has been closed for a relatively long period (several seconds, say), what are the current and capacitor voltage readings, respectively?

2.0 Ω

10 V 2µF

A

V

a. zero A, 10 V b. zero A, zero V c. 5 A, zero V d. 5 A, 10 V