Measuring Electrical Energy

1. Measuring Electrical Energy 11.2 & 11.4

2. Energy: the ability to do work Electrical Energy: energy transferred to an electrical load by moving electric charges. (symbol is E) Joule (J): unit for measuring energy. Because a joule is so small, energy is also measured in much larger units such as the watt hour and the kilowatt hour.

3. Calculation Electrical Energy = Voltage x Electrical Current x Time Interval E = V x I (amps) x Δt (sec) E = V x I x Δt E = V x I x t

4. Question to try Calculate the energy released from a battery in a flashlight bulb that was switched on for 4.5 hours, in which the voltage drop was 6V and the current flowing through the bulb was 0.35A.

5. Question to try Calculate the energy released from a battery in a flashlight bulb that was switched on for 4.5 hours, in which the voltage drop was 6V and the current flowing through the bulb was 0.35A.

6. Convert hours to seconds 1 hour has 60 minutes 1 minute has 60 seconds 60 x 60 = 3600 So 1 hour has 3600 seconds (1 x 3600). 2 hours would have 7200 sec (2 x 3600).

7. E = ?J V = 6V I = 0.35A T = 4.5 hours x 60 270 x 60 16200 sec E = V x I x Δt E = 6V x 0.35A x 16200sec E = 34020 joules

8. Rate at which Energy is Used! • Electrical power is used by us every day – washer, mp3, toaster, discman, etc… • When you think about power – it means, how rapidly an appliance is using up electrical energy. Ex. A 300W bulb uses up 3 times as much electrical energy as a 100W bulb.

9. The symbol for electrical power is P and the unit for power is the watt (W). Power = Voltage Drop x Current P = V x I P = V x I

10. P = V x I V = P I I = P V P V I

11. P = ?W V = 120v I = 7.9A P = V x I P = 120V x 7.9A P = 948 W Calculate the power of a vacuum cleaner if the operating voltage is 120v, and the current flowing through it when it is used is 7.90A.

12. P = 600W V = ? I = 1.9A The voltage would be 316V. V = P I V = 600W 1.9A V = 316V Calculate the voltage of a computer that has 600W of power and 1.9A flowing into the monitor?

13. E = ?J V = 6V I = 0.35A T = 16200 sec *16200sec ÷ 3600 = 4.5 hours E = V x I x t E = 6V x 0.35A x 16200 sec E = 34020 joules The energy released would be 34020 joules. or E = V x I x t E = 6V x 0.35A x 4.5 hours E = 9.45 Whours The energy released would be 9.45 watt hours. Joules to Watt hours

14. P. 336 • Complete questions # 1, 2 and 3a) and 3b)

15. P. 336 – 1, 2, 3a, 3b • Electrical energy is the energy transferred to an electrical load by moving electrons. SI Unit – Joule symbol – J • Voltage drop (potential difference), electric current, time interval

16. E = ?J V = 6V I = 0.30A T = 45 sec E = V x I x t E = 6V x 0.30A x 45 sec E = 81 joules The energy released would be 81 joules. 3a

17. E = ?J V = 9V I = 0.50A T = 2.5 hours E = V x I x t E = 9V x 0.50A x 2.5 hours E = 11.25 watt hours The energy released would be 11.25 Whours. or E = V x I x t E = 9V x 0.50A x 2.5 (3600) E = 40500 joules The energy released would be 40500 joules. 3b

18. Ch. 11 Review Questions • p. 358 # 4, 12, 14, 15 and 16

19. Suggested Unit 2 Review Questions • p. 390-393 • #1, 2 (except k-p), 3 (except l-o), 4, 6, 7, 11, 12, 16, 17, 18, 19, 20 and 24