C
CraftExam
medium importancemedium difficulty5 min

Electric Power

Electric power is the rate at which electrical energy is used or converted in a circuit.

In one line: Power is how fast energy is used.

Practice This Concept

Understand it

Power tells how fast an appliance consumes electrical energy. A device with higher power uses energy more quickly. This is why wattage matters on bulbs, heaters, and other appliances.

Example

A 60 W bulb uses electrical energy faster than a 40 W bulb.

Formula and rule

P = VI, P = I2R, and P = V2/R.

Power is measured in watt.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

  1. 1If a heater works at 220 V and draws 2 A, then P = VI = 220 × 2 = 440 W.
  2. 2So the power is 440 watt.

Method you can reuse

  1. 1See whether voltage and current, or energy and time, are given.
  2. 2Choose the correct power formula.
  3. 3Substitute values carefully.
  4. 4Write the answer in watt.

Sketch it in your answer

Show an appliance label such as a bulb or heater with its wattage written clearly on the device.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

A bulb uses 600 J of electrical energy in 10 s. What is its power?

Think first, then show answer
The power is 60 W because power equals energy divided by time, so 600 divided by 10 gives 60 watt.

Common wrong answer

A common wrong answer is to treat power and energy as the same quantity. Power is the rate of using energy, not the energy itself.

Don't mix this up

Students often confuse power with total energy or think a larger power value means more electricity stored.

Exam tip

Always write power in watt and use the correct relation based on the values given.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Asked as numerical problems, appliance rating questions, or comparisons between two devices.
  1. 1

    Enough for 1 mark

    Electric power is the rate at which electrical energy is used or converted in a circuit.

  2. 2

    Add for 2 marks

    Example: A 60 W bulb uses electrical energy faster than a 40 W bulb.

  3. 3

    Add for 3 marks

    Power tells how fast an appliance consumes electrical energy.

MCQ Quiz

Practice this concept with focused MCQs

Open the concept quiz intro first, review the test details, and then start a focused MCQ set from this concept only. Instant score and answer review are live now.

10 MCQs5 MinutesInstant Results
Practice This Concept

Help improve this page

Found something confusing, incorrect, or missing?

Practice This Concept