1.4.2Electricity, Energy and Waves
Investigating the Cost of Using Appliances — WJEC GCSE Science (Double Award) - Physics Revision Notes & Topical Questions
5 min read 6 parts Lesson 23 of 36
Section 1 of 6Energy rating labels
What they show
- What they show A label states the energy used by the appliance in kWh per year and gives an efficiency band from A (most efficient) to G (least efficient).
- It may also give extra details such as capacity and noise level.
Why they help
- Why they help Two appliances with the same job can cost very different amounts to run, so the label lets buyers compare them fairly.
Changes over time
- Changes over time Older labels used bands such as A+, A++ and A+++,
- but labels have since returned to a simple A to G scale,
- so the details can differ between appliances.
Section 2 of 6Four types of lightbulb
| Bulb | Power rating for similar brightness | Annual cost at 10 p per kWh, left on all year |
|---|---|---|
| LED | 12 W | £10.51 |
| Compact fluorescent (CFL) | 15 W | £13.14 |
| Halogen | 42 W | £36.79 |
| Incandescent | 60 W | £52.56 |
Section 3 of 6Working out an annual cost
1
Convert the power rating to kilowatts by dividing by 1000, so 12 W is 0.012 kW.
2
Find the hours of use in a year; running all day gives 24 × 365 = 8760 hours.
3
Calculate energy used: kWh = power (kW) × time (h), so 0.012 × 8760 = 105.12 kWh.
4
Multiply by the unit price: 105.12 kWh × £0.10 = £10.51.
5
Compare: an LED costs roughly five times less to run than an incandescent bulb giving similar light.
Section 4 of 6Comparing the total cost
Cheapest appliance overall
Running cost
- Running cost Lower power rating for the same output means lower electricity use, so a lower running cost.
Purchase price
- Purchase price Efficient appliances can cost more to buy, so include the buying price when comparing.
Lifetime
- Lifetime An LED can last about 25 000 hours, much longer than other bulbs, so fewer replacements are needed.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Energy label | A label giving an appliance's efficiency band and yearly energy use. |
| Power rating | The rate at which the appliance transfers energy, in watts. |
| Efficiency band | A letter grading, from A (best) to G (worst), of how efficient an appliance is. |
| Lifetime | The average number of hours of use before the device fails. |
| Tariff | The price per kWh charged for electricity. |
Section 6 of 6Exam technique
1
Using watts rather than kilowatts when finding the number of kWh.
2
Using the wrong number of hours in a year; 365 days × 24 hours = 8760.
3
Ignoring purchase price and lifetime when asked which bulb is cheapest overall.
4
Assuming a higher power rating always means better, when it means more energy used.
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