2. Electrical Power P is the _________ at which electrical _____________________________ light, heat, mechanical, etc, energy or vice versa. P P is a _____________ The units of P are watts, W (_____________) Electrical work: W = 1 watt = 1 W = = Since W =, you can write: rate energy is converted to scalar = VI = I 2 R = V 2 /R derived V·A A2·A2· V2/V2/ PtPt VIt = I 2 Rt = V 2 t/R

3. solar power coal power wind power flower power

4. Hint: Read left to right and round down. “Watt” does this meter read? An energy meter. 841 6 kilowatt-hours an energy unit, just like watt-seconds Power Time energy = power x time

6. Ex. At what rate is electrical energy converted to heat and light in a 75 W bulb? 75 W = 75 J/s Ex: A 55-W toaster oven is used for 25 seconds. How much electrical energy is converted to heat? W = Pt = (55 W)(25 s) = 1400 W·s Ex. A 12-  resistor carries a current of 3.0 A for 5.0 s. a/ At what rate does the resistor convert energy? rate  power P = = (3.0A) 2 (12  ) =110 A 2  = 110 W b/ How much energy does the resistor convert in the 5.0 s? W = I 2 Rt = Pt = (110 W) (5.0 s) = 550 W·s = 550 J = 1400 J I 2 R

7. Moses Niagara - 2200 MW = 2.2 GW

8. RAVENSWOOD 2300 MW = 2.3 GW Nine Mile points 1 and 2 620 MW and 1200 MW

9. 9.0 V 50  Ex: How much power is developed in the circuit at right? P = V 2 /R = (9.0 V) 2 / 50  = 1.6 V 2 /  = 1.6 W Given: At what rate is energy converted to heat? P = 1.6 W How much energy is converted in one minute? W = Pt V = 9.0 V R = 50  and = (1.6 W)(60 s) = 96 W·s = 96 J

10. The Flux Capacitor 1.21 GW = 1210 MW = 1210 x 10 6 W

11. V R2R2 R1R1 Ex. R1R1 R2R2 V Power of resistor R 1 : P 1 = V 2 I 2 = VI = or sum up the powers:P = V 1 I 1 = I 1 2 R 1 = V 1 2 /R 1 Power of resistor R 2 : P 2 = I 2 2 R 2 = V 2 2 /R 2 All of these equations work ___________________________. Total power: P = I 2 R eq = V 2 /R eq for both types of circuits seriesparallel P 1 + P 2 + · · ·

12. 5.0 V 20  10  Ex: Find the power in each resistor and the total power. V 1 = I 1 = R 1 = P 1 = 5.0 V 20  10  30  5/30 A 0.17 A 3.3 V 1.7 V 0.17 A V 2 = I 2 = R 2 = P 2 = V = I= R = P = P 1 =V 1 I 1 0.57 W = I 1 2 R 1 = V 1 2 /R 1 0.29 W P = VI = … or P = P 1 + P 2 + · · · 0.83 W

13. 5.0 V 20  10  Ex: Find the power in each resistor and the total power. V 1 = I 1 = R 1 = P 1 = V 2 = I 2 = R 2 = P 2 = V = I= R = P = P 1 =V 1 I 1 = I 1 2 R 1 = V 1 2 /R 1 P = VI = … or P = P 1 + P 2 + · · · 5.0 V 20  10  5/.75 0.50 A 0.25 A 5.0 V 0.75 A 1.25 W 2.5 W 3.8 W 6.7 

14. Which resistor develops more power in the series circuit? Notice both circuits above have ____________V, R 1 and R 2. Which of the two circuits would drain a battery faster? parallel because P is greater Which develops more power in the parallel circuit? ___ b/c both have same ___ but it has more ____________ The ____________ circuit has a ______________ R eq. This means it will have ____________ I. Because P = ______ and both circuits have the _____, the _____________ circuit will develop more power. parallel smaller greater VI V parallel R1R1 I voltage ___ b/c both have same ___ but it has more ____________ R2R2 V current the same

15. __________________ passed ___________ through a wire that was submerged in __________ and found that the amount of ________ produced was proportional to ____ and _____. This is called_________ or _____ heating. Less ___ means ______________ electrical energy is converted to _______. Because P = ____, the current can be reduced if ____ is increased. For this reason, power is transmitted at high _____________. joule Prescott Joule current water heat I2I2 R I2RI2R I much less heat VI V voltages Power plant: ~_____ At your house: _________ The power is transmitted at _____________ A substation cuts the V to __________ 30 kV 155-765 kV 7200 V 240-120 V

16. Why does Europe use 440-220 V instead of 220-110 V? Higher V  can transmit longer distances with less energy loss One transformer can supply an entire block.