Practice Electrical Power in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

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

Power tells you how quickly a device uses energy — a 100 W bulb converts energy twice as fast as a 50 W bulb.

Showing a random 20 of 50 problems.

Example 1

medium
An electric heater uses 1200 W. How much energy in kJ does it consume over 5 minutes?

Example 2

medium
A 12 V battery drives 6 Ω and 4 Ω in parallel. Find the total power delivered.

Example 3

challenge
A 100 kW load is fed by a transmission line with 0.5 Ω total resistance. Compare line power losses if the supply voltage is (a) 1000 V vs (b) 10,000 V.

Example 4

medium
A 12 V battery drives a 6 Ω resistor in series with a 4 Ω resistor. Find the power dissipated in the 6 Ω resistor.

Example 5

hard
If both the current and resistance through a device double, what factor does the power change by?

Example 6

easy
What is the difference between power (watts) and energy (joules)?

Example 7

easy
A 3 Ω resistor carries 2 A. Find the power dissipated.

Example 8

medium
Two resistors 2 Ω and 4 Ω are in parallel across 8 V. Which dissipates more power?

Example 9

easy
A 6 Ω resistor has 12 V across it. Find the power.

Example 10

easy
Write the three equivalent formulas for electrical power.

Example 11

hard
A heater is rated 1500 W at 230 V. What current does it draw, and what is its resistance?

Example 12

easy
A 20 Ω resistor has 10 V across it. Find the power.

Example 13

hard
A motor runs at 80% electrical efficiency. If it draws 5 A at 240 V, what mechanical power does it deliver?

Example 14

medium
An electric kettle rated at 2000 W operates for 3 minutes. How much energy does it use in kJ?

Example 15

medium
A 1500 W microwave runs on 120 V. Find (a) the current it draws and (b) its resistance.

Example 16

medium
A kettle is rated at 2000 W and operates on a 250 V supply. (a) What current does it draw? (b) What is its resistance? (c) How much energy does it use in 3 minutes?

Example 17

easy
If the voltage across a resistor doubles (resistance constant), what happens to the power dissipated?

Example 18

easy
A 10 Ω resistor carries 3 A. Find the power dissipated.

Example 19

medium
An appliance is rated 0.5 kW. How much energy in kilowatt-hours does it use in 3 hours?

Example 20

challenge
A 12 V battery drives a 4 Ω resistor in series with a 2 Ω resistor. Find the power dissipated in each resistor.
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