Page 301 - Schaum's Outline of Theory and Problems of Applied Physics

286 ELECTRIC CURRENT [CHAP. 24

24.14. What is the resistance of a 750-W, 120-V electric iron?

24.15. How much power is developed by an electric motor that draws a current of 4 A when it is operated at 240 V? How
many horsepower is this?

24.16. What is the current in a 100-W light bulb when it is operated at 120 V?

24.17. A 75-W hall light is left on continuously. At $0.09/kWh, find the cost per week.
6
24.18. A 32-V storage battery has a capacity of 10 J. How long can it supply a current of 5 A?
24.19. The 12-V battery of a car is required to be able to operate the 1.5-kW starting motor for a total of at least 10 min.
(a) What should the minimum capacity of the battery be (in ampere-hours)? (b) How much energy is stored in such
a battery?
24.20. A light bulb whose power is 100 W when it is operated at 240 V is instead connected to a 120-V source. (a) What
is the current in the bulb? (b) How much power does it dissipate?

24.21. Currents of 5 A pass through two resistors, one of which has a potential difference of 100 V across it and the other
of which has a potential difference of 300 V across it. (a) Compare the rates at which charge passes through each
resistor. (b) Compare the rates at which energy is dissipated by each resistor.

Answers to Multiple-Choice Questions

24.1. (c) 24.8. (c)

24.2. (b) 24.9. (c)
24.3. (a) 24.10. (a)

24.4. (c) 24.11. (d)

24.5. (a), (c) 24.12. (a)

24.6. (c) 24.13. (d)

24.7. (d)

Answers to Supplementary Problems

24.1. Bends in a wire have no effect on its electric resistance because the electrons whose motion constitutes an electric
current are extremely small with very little mass and therefore can change direction readily.
18
24.2. 3.9 × 10 electrons
24.3. 0.2 A

24.4. 24