Edexcel iGCSE Physics -4.16–4.17 Power, Energy, and Time- Study Notes- New Syllabus

Power: Rate of Energy Transfer

Power describes how quickly energy is transferred or how quickly work is done. Two devices may transfer the same amount of energy, but the one that does it in a shorter time has a greater power.

Definition of Power

Power is defined as the rate of transfer of energy or the rate of doing work.

Power = energy transferred ÷ time taken

\( \mathrm{P = \dfrac{E}{t}} \)

Since work done equals energy transferred:

\( \mathrm{P = \dfrac{W}{t}} \)

• \( \mathrm{P} \) = power (watt, W)
• \( \mathrm{E} \) = energy transferred (joule, J)
• \( \mathrm{W} \) = work done (joule, J)
• \( \mathrm{t} \) = time taken (second, s)

1 watt is defined as 1 joule per second.

Understanding Power

• High power means energy is transferred quickly.
• Low power means energy is transferred slowly.
• Power depends on both energy and time.

Example: A powerful motor lifts an object faster than a less powerful motor, even if both do the same work.

Power and Energy Transfer

• Lifting objects → power depends on how fast the object is lifted.
• Electrical appliances → power shows how quickly electrical energy is used.
• Engines → higher power means faster acceleration or higher speed.

Key Idea

• Power measures speed of energy transfer.
• Same energy in less time means greater power.
• Measured in watts.

Important Points to Remember

• Power is not energy.
• Always use joules and seconds.
• Energy transferred = power × time.