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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:
rateenergy is converted to
scalar
= VI = I2R = V2/R
derived
V·AA2·
V2/
Pt
VIt = I2Rt = V2t/R
solar power
coal power
wind powerflower power
Hint: Read left to right and round down.
“Watt” does this meter read?
An energy meter.
8 4 1 6
kilowatt-hoursan energy unit,just likewatt-seconds
Power Time
energy = power x time
Ex. At what rate is electrical energy converted to heatand 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 A2 = 110 W
b/ How much energy does the resistor convert in the 5.0 s?
W = I2Rt = Pt= (110 W) (5.0 s)
= 550 W·s= 550 J
= 1400 J
I2R
Moses Niagara - 2200 MW = 2.2 GW
RAVENSWOOD2300 MW = 2.3 GW
Nine Mile points 1 and 2620 MW and 1200 MW
9.0 V 50 Ex: How much power is developed in the circuit at right?
P = V2/R = (9.0 V)2/ 50
= 1.6 V2/
= 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
The Flux Capacitor1.21 GW = 1210 MW = 1210 x 106 W
VR2
R1
Ex.
R1 R2V
Power of resistor R1: P1 =
V2I2 =
VI =
or sum up the powers: P =
V1I1 = I12R1 = V12/R1
Power of resistor R2: P2 = I22R2 = V22/R2
All of these equations work ___________________________ .
Total power: P = I2Req = V2/Req
for both types of circuits
series parallel
P1 + P2 + · · ·
5.0 V 20 10
Ex: Find the power in each resistor and the total power.
V1 = I1 = R1 = P1 =
5.0 V
20
10
30 5/30 A
0.17 A
0.17 A3.3 V
1.7 V
0.17 A
V2 = I2= R2 = P2 =
V = I= R = P =
P1 =V1I1
0.57 W
= I12R1
= V12/R1
0.29 W
P = VI = …or P = P1 + P2 + · · ·
0.83 W
5.0 V 20 10
Ex: Find the power in each resistor and the total power.
V1 = I1 = R1 = P1 =
V2 = I2= R2 = P2 =
V = I= R = P =
P1 =V1I1
= I12R1
= V12/R1
P = VI = …or P = P1 + P2 + · · ·
5.0 V
20
10
5/.75
0.50 A
0.25 A5.0 V
5.0 V
0.75 A
1.25 W
2.5 W
3.8 W6.7
Which resistor develops more power in the series circuit?
Notice both circuits above have ____________V, R1 and R2.
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 ______________ Req.
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
R1I voltage
___ b/c both have same ___ but it has more ____________R2 V current
the same
__________________ passed ___________ through a wire that was submerged in __________ and found that the amountof ________ 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 currentwater
heat I2 R
I2R Imuch less heat
VI V
voltages
Power plant:~_____
At your house:_________
The power istransmitted at_____________
A substation cutsthe V to __________
30 kV155-765 kV 7200 V
240-120 V
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.
