1. Electric Circuits
Part 2:
power
With
Ms. Box

2. Important Terms:
Power (P) is measured in watts.
Power is the rate at which electrical energy is transferred by way of a circuit.
You may be more familiar with the term “wattage” to mean the amount of electrical power, in watts.
𝑃=𝐼×𝑉

3. Recall from last time…
If any two of the variables in Ohm’s Law are known, the third value can be found.
Cover up the variable you need to find and you will see the operation of the other two variables that you need to use.

4. Power works similarly, but notice the formula for power (P=IxV) does not include resistance.
If I or V are not given and you need to find the power in a circuit, you will have to use the resistance with Ohm’s law first.

5. Example: If we know that the current is 3 amps and the voltage is 6 volts, what is the power?
𝑃=𝐼×𝑉 𝑃=3×6 𝑃=18 𝑤𝑎𝑡𝑡𝑠

6. Example: If we know that the current is 4 amps and the resistance is 2 ohms, what is the power?
Step 1
Step 2
𝑉=𝐼×𝑅 𝑉=4×2 𝑉=8 𝑣𝑜𝑙𝑡𝑠
𝑃=𝐼×𝑉 𝑃=4×8 𝑃=32 𝑤𝑎𝑡𝑡𝑠

7. What is the power? V = 3 volts Answer: 3 watts I = 1 amp
𝑃=𝐼×𝑉 𝑃=1×3 𝑃=3 𝑤𝑎𝑡𝑡𝑠
V = 3 volts
Answer: 3 watts
I = 1 amp

8. What is the power? V = 426.5 volts Answer: 2021.61 watts I = 4.74 amps
𝑃=𝐼×𝑉 𝑃=4.74× 𝑃= 𝑤𝑎𝑡𝑡𝑠
V = volts
Answer: watts
I = 4.74 amps

9. What is the power? R = 3 Ω Answer: 12 watts I = 2 amps
𝑉=𝐼×𝑅 𝑉=2×3 𝑉=6 𝑣𝑜𝑙𝑡𝑠
R = 3 Ω
𝑃=𝐼×𝑉 𝑃=2×6 𝑃=12 𝑤𝑎𝑡𝑡𝑠
Answer: 12 watts
I = 2 amps

10. BASIC CIRCUIT CHALLENGE
Complete Electrical Power I & II