Energy⏱ 4 min read

Power Formula

P = W / t

What is the Power Formula?

Power is the rate at which work is done or energy is transferred. Two engines can perform exactly the same amount of work, but the more powerful one does it in less time. Power is measured in watts, where 1 watt equals 1 joule per second.

A related version applies to electrical circuits: P = I × V, where power equals current times voltage — the electrical equivalent of the same underlying idea, energy transferred per unit time.

What Each Variable Means

PowerThe rate of energy transfer. (watts (W); 1 W = 1 J/s)

Work / energyThe total energy transferred. (joules (J))

TimeThe time taken to do the work. (seconds (s))

When to Use It

Comparing how quickly different machines or engines can do the same amount of work
Calculating electrical power from current and voltage using P = IV
Estimating energy consumption over time from a known power rating

Step-by-Step Example

Problem: A machine does 600 J of work in 10 seconds. What is its power?

Identify the known values

Work and time are both given.

W = 600 J, t = 10 s

Apply the formula

Divide work by time.

P = 600 / 10

✓

Answer: P = 60 W

Interactive Calculator

W (work/energy) (J)t (time) (s)

Result will appear here

Common Mistakes

Mistake: Confusing power with work or energy.
Fix: Work/energy (Joules) measures the total amount transferred; power (Watts) measures how fast that transfer happens. The same amount of work can correspond to very different power values depending on time.
Mistake: Mixing up P = W/t with the electrical version P = IV.
Fix: Both compute power, but from different quantities — use W/t for mechanical work over time, and IV specifically for electrical circuits with known current and voltage.

Practice Questions

An engine does 5,000 J of work in 25 seconds. Find its power.
A 100 W device runs for 30 seconds. How much energy does it use?
Hint: Rearrange P = W/t to solve for W.