Electrical Power Physics Example 2

Follow the full solution, then compare it with the other examples linked below.

Example 2

medium
A 60 W60 \text{ W} light bulb operates at 120 V120 \text{ V}. What is its resistance and the current it draws?

Solution

  1. 1
    Current: I=PV=60120=0.5 AI = \frac{P}{V} = \frac{60}{120} = 0.5 \text{ A}
  2. 2
    Resistance: R=VI=1200.5=240 ΩR = \frac{V}{I} = \frac{120}{0.5} = 240 \text{ } \Omega
  3. 3
    Or directly: R=V2P=1440060=240 ΩR = \frac{V^2}{P} = \frac{14400}{60} = 240 \text{ } \Omega.

Answer

I=0.5 A,R=240 ΩI = 0.5 \text{ A}, \quad R = 240 \text{ } \Omega
Electrical power can be expressed in multiple forms: P=VI=I2R=V2/RP = VI = I^2R = V^2/R. These are all equivalent and useful in different situations.

About Electrical Power

The rate at which electrical energy is converted to other forms of energy (heat, light, motion). Measured in watts (W).

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More Electrical Power Examples

Example 1 easy

A device draws [formula] from a [formula] outlet. What is the electrical power consumed?

Example 3 medium

An electric kettle rated at [formula] operates for [formula]. How much energy does it use in kJ?

Example 4 medium

A kettle is rated at [formula] and operates on a [formula] supply. (a) What current does it draw? (b

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