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What About
Watts?
4.2.3B Electrical Power
Power Law
• Moving electrons (current) requires ENERGY
• How much energy gets used depends on:
• Strength of push – VOLTAGE
• Rate of flow – CURRENT
V2
PI VIV
2
P  IV  R  I R
R
Example #1
• A 12 volt battery is connected to a circuit which
allows 10 amperes of current to flow.
– What is the power output of this circuit?
P = IV
P = (12 V)(10 A)
P = 120 W
Example #2
• A 100 watt light bulb is connected to a 120 volt power
supply.
– What amount of current must pass through the light bulb?
P = IV
100 W = (120 V) I
I = 0.833 A
Example #3
• A 2.0 ampere current passes through a circuit with a
300 ohm resistance.
– What is the power generated in this circuit?
P = I2 R
P = (2.0 A)2 (300 Ω)
P = 1200 W or 1.2 kW
End of 4.2.3B – PRACTICE