Reasoning questions give a circuit, a graph or a table and ask you to predict or explain. It is part of SPM Physics electricity and has four lessons and a practice set.
What does this section cover?
Start with predicting what an open branch changes in a conceptual circuit. Then compare potential difference readings without changing the circuit.
The third is explaining a non-linear current-voltage graph from supplied measurements. The last is separating electrical energy from power in a fictional appliance table. The practice set mixes all four.
One circuit, four kinds of question
Take this original example. A 6 V supply feeds two identical lamps in parallel, each of resistance 12 Ω.
| Question type | What you are asked | Key idea |
|---|---|---|
| Open branch | What happens if one lamp is removed? | The other branch still has 6 V |
| Comparing readings | What does each voltmeter show? | Same p.d. across parallel branches |
| Graph from data | Why is V ÷ I not constant for a lamp filament? | Resistance rises with temperature |
| Energy and power | Which appliance uses more energy? | Energy depends on power and time |
Each branch carries 0.5 A, so the supply delivers 1.0 A. Remove one lamp and the supply delivers 0.5 A, while the remaining lamp stays as bright as before.
Who should start where?
If you are unsure what changes when a switch opens, begin with the open-branch lesson. If voltmeter readings confuse you, begin with comparing readings.
If a curved graph shows up in your paper, begin with the non-linear graph lesson. If kWh and watts keep blurring, begin with the energy and power table lesson.
For a teacher to go through your written answers, see online one-to-one Physics tuition or try the one-hour trial class (from RM50).