Transcript Electric Power

Electric Power
2
V
P  IV  I R 
R
2
Example: Electric Heater
An electric heater draws 15.0 A on a 120-V line. How much
power does it use and how much does it cost per month (30 days)
if it operates 3.0 h per day and the electric company charges 10.5
cents per kWh? (For simplicity, assume current flowing in one
direction).
Lightning Bolt
Typical lightning bolt can transfer 109 J of energy across a
potential difference of perhaps 5x107 V during a time interval of
about 0.2 s. Use this information to estimate the total amount of
charge transferred, the current, and the average power over the
0.2 s.
Power in Household Circuits
Will a Fuse Blow?
Define the total current drawn by all devices in the
circuit shown in the next slide.
Alternating Current
V  V0 sin 2ft
V V0
I   sin 2ft
R R
2
2
2
P  I R  I 0 R sin 2ft
Average Power
1 2
P  I0 R
2
2
1 V0
P
2 R
Root-Mean-Square Values (RMS)
I rms
Vrms
I0
 I 
 0.707 I 0
2
V0
2
 V 
 0.707V0
2
2
Stereo Power
Each channel of stereo receiver is capable of an average
power output of 100 W into a 8-W loudspeaker. What is the
rms voltage and rms current fed to the speaker at the
maximum power of 100 W?