rateat which electrical Electrical Power P is the

rateat which electrical Electrical Power P is the _____ energy is converted to _______________ light, heat, mechanical, etc, energy or vice versa. scalar P is a _______ P = VI = I 2 R = V 2/R The units of P are watts, W (_______) derived 1 watt = 1 W = V·A = A 2·W = V 2/W Since W = Pt , you can write: Electrical work: W= VIt = I 2 Rt = V 2 t/R

coal power solar power flower power wind power

An energy meter. “Watt” does this meter read? Hint: Read left to right and round down. 8 4 1 6 kilowatt-hours an energy unit, just like watt-seconds Power Time energy = power x time

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 = 1400 J Ex. A 12 -W resistor carries a current of 3. 0 A for 5. 0 s. a/ At what rate does the resistor convert energy? rate power P = I 2 R = (3. 0 A)2(12 W) =110 A 2 W = 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

Moses Niagara - 2200 MW = 2. 2 GW

RAVENSWOOD 2300 MW = 2. 3 GW Nine Mile points 1 and 2 620 MW and 1200 MW

Ex: How much power is developed in the circuit at right? Given: V = 9. 0 V P = V 2/R 50 W 9. 0 V and R = 50 W = (9. 0 V)2/ 50 W = 1. 6 V 2/ W = 1. 6 W At what rate is energy converted to heat? P = 1. 6 W How much energy is converted in one minute? W = Pt = (1. 6 W)(60 s) = 96 W·s = 96 J

The Flux Capacitor 1. 21 GW = 1210 MW = 1210 x 106 W

Ex. series parallel R 1 V V R 2 Power of resistor R 1: P 1 = Power of resistor R 2: P 2 = Total power: or sum up the powers: P = P= R 2 R 1 V 1 I 1 = I 12 R 1 = V 2 I 2 = I 22 R 2 = VI = I 2 Req = V 12/R 1 V 22/R 2 V 2/Req P 1 + P 2 + · · · for both types of circuits. All of these equations work ______________

Ex: Find the power in each resistor and the total power. 20 W 5. 0 V P 1 =V 1 I 1 10 W = V 12/R 1 = I 12 R 1 V 1 = 3. 3 V I 1 = 0. 17 AR 1 = V 2 = 1. 7 V I 2= 0. 17 A V = 5. 0 V I= 5/30 A 0. 17 A P 1 = 20 W 0. 57 W R 2 = 10 W P 2 = 0. 29 W R= 30 W P= 0. 83 W P = VI = … or P = P 1 + P 2 + · · ·

Ex: Find the power in each resistor and the total power. 20 W 5. 0 V 10 W P 1 =V 1 I 1 = V 12/R 1 = I 12 R 1 20 WP 1 = V 1 = 5. 0 V I 1 = 0. 25 AR 1 = V 2 = 5. 0 V I 2= 0. 50 A R 2 = 10 W P 2 = 2. 5 W V = 5. 0 V I= 0. 75 A R= 5/. 75 6. 7 W P= 3. 8 W 1. 25 W P = VI = … or P = P 1 + P 2 + · · ·

the same 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 smaller Req. parallel The ______ circuit has a _______ greater I. Because This means it will have ______ V P = ______ VI and both circuits have the _____ , the parallel _______ circuit will develop more power. Which resistor develops more power in the series circuit? R 1 b/c both have same ___ but. I it has more ______ voltage ___ Which develops more power in the parallel circuit? R 2 b/c both have same ___ but. Vit has more ______ current ___

Prescott Joule current through a wire that _________ passed ______ water and found that the amount was submerged in _____ heat produced was proportional to ____ and. I 2_____. R of ____ joule or _____ I 2 Rheating. Less ___ means I This is called_____ much less _______ electrical energy is converted to _______. heat Because P = ____VI, the current can be reduced if ____ is V increased. For this reason, power is transmitted at high voltages _______. At your house: 240 -120 V _____ Power plant: 30 k. V ~_____ The power is transmitted at 155 -765 k. V _______ A substation cuts 7200 V the V to _____

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.