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O-Level Practical Electricity

What the O-Level syllabus expects for Practical Electricity, and how to practise it.

What the syllabus expects

Describe how the heating effect of electricity is used in appliances like electric kettles, ovens and heaters.
Recall and use P = VI and E = V It in unfamiliar situations or problem solving.
Work out the cost of running electrical appliances where energy is charged in kW h.
State the electrical hazards arising from damaged insulation, overheating cables, and damp conditions.
Explain the role of fuses and circuit breakers in circuits and of fuse ratings.
Explain why earthing metal casings and double insulation are needed.
State what the terms live, neutral and earth mean.
Describe the wiring inside a mains plug.
Explain why the live wire is the one fitted with switches, fuses and circuit breakers.

How it's examined

Questions on this topic most often ask you to find. About 3% of the past-paper style questions in Rae's bank for this subject sit in this topic.

Worked examples

Example 1 (2 marks)

An electric oven runs on a 220 V supply and contains a heating element whose resistance is 25 ohm. (a) Work out the rate at which the oven uses energy.

Show the worked answer

Rate of energy use is the power dissipated. P = V² / R = 220² / 25 = 48400 / 25 = 1936 W.

Example 2 (2 marks)

An electric oven runs on a 240 V supply. Its heating element has a resistance of 30 ohm. (b) In Singapore, one kWh of electricity costs 32 cents. Find the total electricity cost of running this oven for 3.0 hours every day over one week.