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1. A hairdryer with a power of 1.5 kW means that it
transforms 1500 joules of electrical
energy each second.
2. Total units used
= 03102 - 02586
Total
units used = 516 kWh
Cost
of electrical energy used = 516 x 9 pence
Cost
of electrical energy used = £46.44
3. The
control variable was the length
of time.
4. Table to find the cost of using
the appliances. The cost is 9 pence per kWh.
| Devices |
Power |
Time |
Cost |
| Electric
cooker |
5 kW |
2
hours |
5 x 2 x 9 = 90 pence |
| Light
bulb |
100 W |
2 hours |
0.1 x 2 x 9 = 1.8 pence |
| Computer |
120 W |
30
minutes |
0.12 x 0.5 x 9 =
0.54 pence |
| Kettle |
2 kW |
15 minutes |
2 x 0.25 x 9 = 4.5 pence |
5. Higher tier only:
Number of kilowatt-hours produced is the energy transferred.
Energy transferred = power x time
Energy transferred = (25/1000 x 1/5) x 24 Hint: Power in kilowatt & time in hour
Energy transferred = 0.12 kWh
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