Power Rating
- Figure above is an example of power rating label.
- 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.
Example
A bulb rated 240V/80W is operated from a 120V power source. Find the resistance and the current flows through it.
Answer:
The current flows through the bulb
Energy Consumption
Calculating the cost of electricity consumption
- The amount of electrical energy consumed in a given time:
- The larger the power rating in the electrical appliance, the higher energy is used for every second.
- The longer the usage time, the higher electrical energy is consumed.
- The cost of electricity consumption is based on the number of kilowatt-hours (kWh) of electrical energy used.
- The kilowatt-hours are sometimes known as the domestic units of electricity.
- 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
Example:
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.
Answer:
Electrical energy consumed by the kettle,
Electrical energy consumed by the bulb,
Total energy consumed,
The Cost
= 0.66×22cent=14.52cent