The method and the results are on the electrical power lab. Do the analysis yourself first, then check the answers below.
Quick answer: Electrical power is the rate at which an appliance transfers energy, measured in watts. These answers go with the grade 8 science lab on electrical power: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
Model answers use the sample table. Your own values will differ a little, but the trends should match: power rises with voltage, and it rises faster than the voltage because the filament heats up.
2.0 V: 0.40 W 4.0 V: 1.24 W 6.0 V: 2.28 W 8.0 V: 3.52 W 10.0 V: 4.80 W 12.0 V: 6.24 W The 12 V value is close to the lamp’s 6 W rating.
Question 2 Graph of power against voltage
The points rise in a curve that gets steeper: the power increases by 0.84 W between 2 and 4 V but by 1.44 W between 10 and 12 V. Power rises faster than the voltage, so the graph is not a straight line.
Question 3 Energy in one minute
E = P × t = 6.24 W × 60 s = 374.4 J, so 374 J to 3 significant figures.
Question 4 Running cost
E = 0.00624 kW × 5 h = 0.0312 kWh. Cost = 0.0312 × 20 p = 0.624 p, so about 0.62 p.
Question 5 Voltage and current ratios
I rose from 0.20 A to 0.52 A, a factor of 0.52 ÷ 0.20 = 2.6. The filament gets hotter and hotter, and a hot filament lets less current through for the same voltage, so the current rises more slowly than the voltage.
Switch the lamp off between readings so the filament always starts cold, and read the meters straight away; also use meters with a finer scale. Any two sensible changes earn full credit.
