Power

Now you know what volts, ohms, and amps are. What about watts? What's the difference between a 60-watt bulb and a 100-watt bulb. Watts have to do with the power output of the bulb, or how much work that bulb can do in a specific amount of time.

The electric power of a light bulb is equal to the product of the current times the voltage in the circuit. The unit of electric power is the watt (W).

Electric Power

$\large\mathsf{P = IV }$

Question

You know that Ohm's Law states that $\mathsf{V = IR }$ . How is power related to the resistance of a circuit?

Since

$\mathsf{V = IR }$ , solving for I gives you

$\mathsf{I = \frac{V}{R} }$ . If you substitute that into the power equation, you get

$\mathsf{P = \frac{V^2}{R} }$ . Power is inversely proportional to the resistance in the circuit. In other words, the higher the resistance, the lower the power; the lower the resistance, the higher the power. You use more power through a circuit with less resistance.

You could also just substitute IR in for V and get yet another version of the power equation:

$\mathsf{P = I^2 R }$ .

Question

Calculate the wattage of a light bulb that carries 0.625 A of current and is connected to a 120 V source?

$\mathsf{P = IV }$

$\mathsf{P = 0.625 \text{ A} \times 120 \text{ V} }$

$\mathsf{P = 75 \text{ W} }$

What is electrical power?

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