1. Electrical Power is rate at which energy flows
Power (P) is measured in Watts (W)
Power = current x voltage
P = I x V
Divide
Multiply
So, to find Current, we need to DIVIDE power by voltage.
I = P V P
watts I V
And, to find Voltage, we need to DIVIDE power by current.
V = P I
amps
volts

2. Where do Power Units come from?
Power = Voltage x Current
Joules Joules Coulomb
second Coulomb second
(Watts) (volts) (amps) = x

3. Electrical Power Problem
If a CD player uses 4.5 V with 0.2 amps of current, what is the power it uses?
P= I x V
P = ?
P =
0.2 A x 4.5 V
I =
0.2 A
P = 0.9 Watts
V =
4.5 V

4. Do the Practice Problem

5. Is measured in kilowatt-hours Electrical Energy = power x time
Kilo means 1000x
Electrical Energy = power x time
E = P x t
Divide
Multiply
So, to find power, we need to DIVIDE energy by time.
P = E t E
kWhr
And, to find time, we need to DIVIDE energy by power.
t = E P P kW t hr

6. Electrical Energy Problem
You use your hairdryer for 10 minutes everyday. The hairdryer uses watts. How many kilowatt-hours does your hairdryer use in 12 days?
E = P x t
E = 1 kW x 0.17 hr
E =
P =
1000 W = 1 kW
0.17 x 12 days= 2 kWhr
t =
10min / 60 = 0.17 hr

7. Do the Practice Problems