Paying For Electricity
This lesson covers:
- How electricity usage is measured in kilowatt-hours (kWh)
- Calculating the energy usage and cost for electrical appliances
- The importance of saving energy to reduce environmental impacts
- Energy efficient technologies like LED bulbs and appliances with energy ratings
Electricity usage is measured in kilowatt-hours
Electricity companies charge for units of energy called kilowatt-hours (kWh).
The energy used by an appliance depends on its power and time used:
E = P x t
Where:
E = energy used (kWh)
P = power (kW)
t = time (h)
For example, a 1,500 W hairdryer used for 10 minutes uses 0.25 kWh or 900,000 J.
Calculating energy usage and costs
The cost of electricity can be calculated using:
cost = energy used x price
Where:
cost = cost of electricity used (£)
number of kilowatt hours used = energy used (kWh)
price = price per kWh (£)
Worked example - Calculating the energy usage and cost of a television
Calculate the energy usage in kWh and cost of running a 120 W television for 5 hours if electricity costs 20p per kWh.
Step 1: Formula
energy used = power × time
Step 2: Calculate the energy used
Energy used = 0.12 kW × 5 h = 0.6 kWh
Step 3: Formula for cost of electricity
cost = energy used × price
Step 4: Calculate the cost
cost = 0.6 × 0.20 = £0.12
Saving energy is important
Producing electricity has environmental impacts including:
- Carbon dioxide emissions
- Air pollution
- Radioactive waste
- Large land use
Using energy efficient appliances helps reduce these impacts and save money.
Examples include:
- LED lightbulbs - More efficient and longer-lasting than traditional bulbs.
- Energy rated appliances - Washing machines/ovens with rating to indicate efficiency.