Power Rating

Power Rating

  1. Figure above is an example of power rating label.
  2. An electrical appliance which is marked 240V, 1200W means that the electrical appliance will consume 1200J of energy in every second if the potential difference across it is 240V.

A bulb rated 240V/80W is operated from a 120V power source. Find the resistance and the current flows through it.


The current flows through the bulb

Energy Consumption

Calculating the cost of electricity consumption

  1. The amount of electrical energy consumed in a given time:
  2. The larger the power rating in the electrical appliance, the higher energy is used for every second.
  3. The longer the usage time, the higher electrical energy is consumed.
  4. The cost of electricity consumption is based on the number of kilowatt-hours (kWh) of electrical energy used.
  5. The kilowatt-hours are sometimes known as the domestic units of electricity.
  6. The kilowatt-hour (kWh) is the energy used by a device at a rate of 1000 watts in one hour.
    1 kWh = (1000 W) × (60 × 60 s) = 3.6 MJ

If TNB charges 22 cents for each kWh of electrical energy used, calculate the total cost of using a 2kW electric kettle for 15 minutes and a 20 W filament bulb for 8 hours.

Electrical energy consumed by the kettle,

Electrical energy consumed by the bulb,

Total energy consumed,

The Cost
= 0.66×22cent=14.52cent