WATT INTO JOULE

JOULE (J) AND WATT (W)

ENERGY • POWER • TIME

Joule and Watt are two closely related units in physics, but they measure different quantities.

1. Joule (J) — Energy

The joule (J) is the SI unit of energy, work, and heat.

• Measures the amount of energy transferred or used.
• Example: 100 joules of energy.
• Symbol: J

2. Watt (W) — Power

The watt (W) is the SI unit of power, which describes the rate at which energy is transferred or used over time.

• Measures how quickly energy is used.
• Example: a light bulb rated at 10 watts.
• Symbol: W

THE RELATIONSHIP

1 Watt = 1 Joule per Second

P = E / t

P = Power (W)
E = Energy (J)
t = Time (s)

E = P × t

Energy = Power × Time

CALCULATION EXAMPLE

Suppose an electrical device has a power rating of 100 watts and operates for 10 seconds.

E = 100 × 10

E = 1,000 J

The device uses 1,000 joules of energy in 10 seconds, assuming constant power.

JOULE–WATT CALCULATOR

Use these formulas to calculate energy, power, or time.

Calculate Energy

Formula: E = P × t

Multiply power in watts by time in seconds to obtain energy in joules.

Calculate Power

Formula: P = E / t

Divide energy in joules by time in seconds to obtain power in watts.

Calculate Time

Formula: t = E / P

Divide energy in joules by power in watts to obtain time in seconds. Power must be greater than zero.

COMPARISON TABLE

Aspect	Joule (J)	Watt (W)
Physical quantity	Energy	Power
Meaning	How much energy	How quickly energy is used
Water analogy	Total volume of water	Water flow rate
Electrical example	Energy consumed	Device power rating

WHAT IS A KILOWATT-HOUR?

Electricity consumption on utility bills is commonly measured in kilowatt-hours (kWh), rather than in watts alone.

1 kWh = 3,600,000 J

One kilowatt-hour is the energy used by a 1,000-watt device operating for one hour.

KEY TAKEAWAY

Joule measures the amount of energy.

Watt measures the rate at which energy is transferred or used.

Time connects the two quantities.

PHYSICS FUNDAMENTALS | ENERGY • POWER • TIME