watt – unit of power, equivalent to one joule of work being done in one second

(pronounced wot)

To remember the meaning of watt, use the following mnemonic:

The watch (watt) required a significant amount of power to move its jewel-encrusted second (joule per second) hand.

Also recall the physics electrical formula mnemonic:

Here you can clearly see the power (watts) is energy (joules) over time (seconds).

The watt is the standard unit of power, which measures the rate at which energy is transferred or work is done per unit of time. One watt is defined as the transfer of one joule of energy per second. The equation for this is: 

Power (w) = energy transferred (j) ÷ time (s)

or alternatively

Power (w) = work done (j) ÷ time (s)

This means a device with a power rating of 100 watts transfers 100 joules of energy every second, whether that energy is being converted from electrical energy to light and heat in a light bulb, or from chemical energy to kinetic energy in a motor.

Common power ratings range from a few watts for LED bulbs and phone chargers, to hundreds of watts for laptops and televisions, to thousands of watts (kilowatts) for household appliances like kettles, ovens, and electrical heaters. 

If a fan heater is known to have an energy output of 120,000 joules per minute, the wattage can be calculated as follows:

`\text(Power)  =  \text(work done)/(\text(time)(\text(seconds))`

`\text(Power)  =  (120,000  \text(J))/60`

`\text(Power)  = 2000\text(w)`

Wattage can also be calculated by multiplying potential difference (voltage) and current (amps), as displayed in the following formula:

Power = voltage (v) x current (amps)

For example, if a light bulb operates at 230 volts and draws a current of 0.5 amp, the power it consumes can calculated using:

Power = 230 volts x 0.5 amps

Power = 115 watts