# Electricity: Power of Electrical Appliances

## Power of Electrical Appliances

• The power (P) of an electrical appliance is the rate at which it transfers energy.

• Power is measured in watts (W). 1 watt is equivalent to 1 joule of energy transferred per second.

• The power of an appliance can be calculated from the formula P = VI, where V is the voltage across it and I is the current passing through it.

• For an appliance using alternating current (AC), as most household appliances do, this formula can also be written as P = VIcosθ, where cosθ is the power factor.

• A device’s efficiency can also be found by comparing the power output to the power input. The more efficient an appliance is, the less energy is wasted in forms such as heat or sound.

## Energy Consumption of Electrical Appliances

• The total energy an appliance transfers can be calculated with the formula E = Pt. E is energy (in Joules), P is power (in Watts), and t is time (in seconds).

• For everyday purposes, it’s often more practical to work with energy in kilowatt-hours (kWh) and time in hours. 1 kWh is equivalent to 3.6 million joules.

• The number of kilowatt-hours an appliance uses can be found by multiplying its power (in kilowatts) by the time it’s used (in hours).

• An appliance’s energy use can help determine its cost to run. Simply multiply the amount of energy consumed in kilowatt-hours by the cost per kilowatt-hour.

• The energy efficiency of appliances is a critical concern in terms of cost and environmental impact. The more efficient an appliance, the less energy it uses for the same output, and therefore the lower the cost and the smaller the environmental impact.

Mastering these concepts is instrumental in understanding the power and energy consumption of electrical appliances.