Asignment
1. A 12V battery is connected across a 10 ohm resistor. How many joules of energy will be dissipated in 30 seconds?
(a) 7200 J
(b) 864 J
(c) 432 J
(d) 120 J
(e) 14.4 J
2. A power line is 5 km long and has a resistance of 0.7 ohms. The current flowing is 10 amperes. What is the power dissipated in the line resistance?
(a) 7 W
(b) 14 W
(c) 70 W
(d) 14 kW
Use the following situation to answer questions 5, 6, 7, and 8: A motor is rated to deliver (output) 2.5 hp at 120V DC. (Reminder, input power is always greater than output power, and remember to use a horsepower conversion: 1 horsepower ≈ 746 watts)
3. If the motor runs on 120V and is 75% efficient, how many watts does it draw from the power line (input)?
(a) 2487 W
(b) 2072 W
(c) 1679 W
(d) 1399 W
(e) 3.33 W
4. What is the input current?
(a) 20.7 A at 75% efficiency
(b) 17.3 A at 75% efficiency
(c) 14.0 A at 75% efficiency
(d) 11.7 A at 75% efficiency
(e) 28 mA at 75% efficiency
(f) 28 mA at 90% efficiency
5. What is the input current if the motor is boosted to 90% efficient?
(a) 20.7 A at 75% efficiency
(b) 17.3 A at 75% efficiency
(c) 14.0 A at 75% efficiency
(d) 11.7 A at 75% efficiency
6. Assuming the motor is run 24 hours a day, for 365 days, what is the cost difference for electricity over a year for a motor that is 75% efficient and one that is 90% efficient assuming $0.10 per kWh?
(a) $2175.98
(b) $1818.58
(c) $922.24
(d) $735.20
(e) $357.41
Use the following situation to answer questions 9, 10, 11, 12, and 13: Eight holiday lights, each having the same resistance, are connected in series with 120 V DC supply powering them. Each of the eight bulbs has an internal resistance of 60 ohms.
7. Determine the total resistance of the network.
8. What is the current through the bulbs?
9. Determine the power delivered to each individual bulb (NOT THE SOURCE POWER).
10. Calculated the voltage drop across each bulb.
11. What would happen if one of the bulbs burned out (infinite resistance)?
(a) None of the bulbs would be lit.
(b) The other bulbs would remain lit, but not as bright, since less current flows through each bulb.
(c) The other bulbs would remain lit, but brighter, since more current flows through each bulb.
(d) The other bulbs would remain lit with the same brightness as before.
Use the following situation to answer questions 14, 15, 16, 17, and 18: Eight holiday lights, each having the same resistance, are connected in parallel with 120 V DC supply powering them. Each of the eight bulbs has an internal resistance of 60 ohms.
12. Determine the total resistance of the network.
13. What is the current through the bulbs?
14. Determine the power delivered to each individual bulb (NOT THE SUPPLY POWER).
15. Calculated the voltage drop across each bulb.
16. What would happen if one of the bulbs burned out (infinite resistance)?
(a) None of the bulbs would be lit.
(b) The other bulbs would remain lit, but not as bright, since less current flows through each bulb.
(c) The other bulbs would remain lit, but brighter, since more current flows through each bulb.
(d) The other bulbs would remain lit with the same brightness as before.