AP Physics 1 U8 FRQShow all work on separate paper. Write formulas used, show substitution, and include units.

1. How many excess electrons does it take to have a charge of -9.4 μC? (5.88x1013 electrons)

2. What is the charge on 8.42 x107 electrons? (-1.35x10 -11 C)

3. Two small, identical metal spheres contain excess charges of -10.0µC and +6.0µC, respectively. The spheres are mounted on insulated stands and placed 0.40 m apart. a) Determine the magnitude and direction of the force between the spheres. b) The spheres are touched together and then returned to their original 0.40 m separation. Determine the magnitude and direction of the force between the spheres.

(a) -3.4 N attraction b) 0.23 N repulsion)

4. Two identical pith balls are suspended from the same point by light strings 1.0 meters long. The balls each have a mass of 0.0020 kg and carry equal amounts of positive charge with the result that the balls are separated by 0.050 meters. Determine the magnitude of the electric charge on each ball.

(1.2 x 10-8 C)5. Which of the following wires would have the least resistance?

a. a copper wire 10 cm in length at 32˚Cb. a copper wire 5 cm in length at 32˚Cc. a copper wire 10 cm in length at 10˚Cd. a copper wire 5 cm in length at 10˚C (D – explain)

6. Josh is going trick-or-treating for Halloween so he puts new batteries in his flashlight before leaving the house. Until the flashlight shuts off, its draws 0.500 A of current, allowing a total of 5400. C of charge to flow through the circuit. How long will Josh be able to use the flashlight before the batteries’ energy is depleted?

(3.0 hours)

7. Debbie’s car radio will run from the 12-V car battery that produces a current of 0.20 A even when the car is turned off. The car battery will no longer operate when it has lost 1.2 x 106 J of energy. If Debbie get gets out of the car and leaves the radio on by mistake, how long will it take for the car battery to go completely dead (that is, lose all energy) (139 hours)

8. While cooking dinner, Marco’s oven uses 220 V and draws 8.00 A of current when heated to its maximum temperature. What is the resistance of the oven when it is fully heated? (27.5 Ω)

9. Jasmine’s hair dryer has a resistance of 9.00 Ω when first turned on. a.) How much current does the hair dryer draw from the 110 V line in Justine’s house? b) What happens to the resistance of the hair dryer as it runs for a long time? (a. 12.2 A) (b. resistance increases as temperature increases)

10. Sarah takes her pocket calculator out of her book bag as she gets ready to do her physics homework. In the calculator, a 0.160 C charge encounters 10.0 Ω of resistance every 2.00 seconds. What is the potential difference of the battery? (0.80 V)

11. How much power is used by a contact lens heating unit that draws 0.070 A of current from a 120-V line? (8.4 W)

12. Leah’s air conditioner uses 2160 W of power as a current of 9.0 A passes through it. a) What is the voltage drop when the air conditioner is running? b) How does this compare to the usual household voltage? c) What would happen if Celeste tried connecting her air conditioner to a usual 120-V line? (a. 240 V) (b. Double) (c. I=18 A….blow a fuse)

13. Which has more resistance when plugged into a 120-V line, 1400-W microwave oven or a 150-W electric can opener? (can opener: 96 Ω)

14. You left a 120 W light bulb turned on in your room & it stayed on for 12 hours. Your parents want you to pay for the wasted energy. If Edison charges $0.17 per kWh, how much do you owe your parents (about 25¢)

15. A pocket calculator draws 5.0 x 10-5 A of a current when connected to a 9.0 V battery. a) What power does the calculator use? (4.5 x 10-4 W)b) How much energy does the calculator use if it is left on for 20.0 minutes? (0.54 J)

16. What is the voltage of the battery if a 0.70 A current flows through a 15Ω light bulb? (10.5 V)

17. A toaster when connected to a 120 V outlet uses electrical energy at the rate of 1500 W. a) what is the current through the toaster? b) What is the resistance of the toaster? (a. 12.5 A) (b. 9.6 Ω)

18. a) How much energy does a 150 W light bulb use in 2.0 hours? b) If the light bulb is 20.0% efficient, how much heat does it generate? (a. 1.08 x 106 J) (b. 8.64 x 105 J)

19. Name two ways to decrease the current in a circuit. (increase ?, decrease ?)

20. In a circuit with a constant resistance, we replace the battery with one that has four times the original voltage. What would be the effect on the current? What would be the effect on the power? (4 x I, 16 x P)

21. Sean is playing with a new electronics kit he has received for his birthday. He takes out four resistors with resistance of 15 Ω, 20 Ω, 20 Ω, and 30 Ω. A) How would Sean have to wire the resistors so that they would allow the maximum current to be drawn? Calculate the total resistance in this current. b) How must he wire the resistors so that they draw a minimum amount of current? Calculate the total resistance in this circuit.

a) Parallel. 5.0 Ω b) Series, 85 Ω

22. Old fashioned holiday lights were connected in series across a 120-V household line. a) If a string of these lights consists of 12 bulbs, what is the potential difference across each bulb? b) If the bulbs were connected in parallel, what would be the potential difference across each bulb? a) 10 V b) 120 V

23. A 10 Ω resistor, a 20 Ω resistor and a 30 Ω resistor are connected in series with 120 V source. a) What is the effective resistance of the circuit? (60 Ω)b) What is the current in the circuit? (2.0 A)c) What is the power drop across the 20 Ω resistor? (80 W)

24. Before going to work each morning, Gene runs his 18 Ω toaster, 11 Ω electric frying pan, and 14 Ω electric coffee maker, all at the same time. The three are connected in parallel across a 120 V line. a) What is the current through each appliance? b) If a household circuit could carry a maximum current of 15 A, would Gene be able to run all of these appliances at the same time.

a) toaster: 6.67A, frying pan:10.91 A, coffee maker: 8.57A b) No, 26.16 A

25. A 10 Ω resistor, a 20 Ω resistor and a 30 Ω resistor are connected in parallel with 120 V source. a) What is the effective resistance of the circuit? (5.45 Ω)b) What is the current through the 20 Ω resistor? (6.0 A)

26. A 15 Ω resistor is connected in series with two 10 Ω resistors in parallel and a 120 V generator. a) What is the total current in the circuit? (6.0 A)b) What is the current through the 10.0 Ω resistor? (3.0 A) c) What is the voltage drop across the 15.0 Ω resistor? (90 V)

27. The following appliances are all connected in parallel with a 120 V source in one of the lines in the electrical system of a house: 15 Ω electric frying pan, a 25 Ω refrigerator, a 20 Ω heater, and a 12 Ω toaster. The fuse in this line melts at 28 A. Will this arrangement of appliances cause the fuse to melt? Justify your answer.

(The fuse will melt. R = 4.17 Ω, so the current will be 28.8 A)

28. A 56 Ω resistor and another resistor are connected in parallel across a 12 V battery. The current in the circuit is 3.21 A. Find the unknown resistance. (4.0 Ω)

29. For each circuit shown on the back, find the effective resistance and the total current through the circuit. Then find I and V for any * resistors

16 Ω 5 Ω* 4 Ω

10 V

18 Ω*

4 Ω

36 Ω

36 V

32 V

15 Ω

6 Ω10 Ω *