These six original questions increase in difficulty. Write each answer on paper before you open its explanation.
The set belongs to SPM subjects and learning resources. The structured answer self-review tool helps you check your working.
Questions
Question 1: A circuit has a battery, a closed switch and a lamp in one loop. Describe the path of conventional current (2 marks).
Answer
Current flows from the positive terminal of the battery, through the closed switch, then the lamp, and back to the negative terminal. The loop is complete, so the lamp lights.
Question 2: The switch in Question 1 is opened. Explain what happens to the lamp (2 marks).
Answer
The open switch is a gap in the loop, so there is no complete path for current. The current is zero everywhere in the loop, and the lamp goes out.
Question 3: A 12 V supply is connected across a 3.3 kΩ resistor. Find the current in mA (3 marks).
Answer
Convert: 3.3 kΩ = 3 300 Ω.
I = 12 ÷ 3 300 = 0.003 636 A, which is about 3.64 mA.
Sense check: a few volts across a few kilo-ohms gives a few milliamps.
Question 4: A 5 V supply powers an LED that drops 2 V and needs 15 mA. Find the series resistor (3 marks).
Answer
Voltage across the resistor = 5 − 2 = 3 V.
Current = 15 mA = 0.015 A.
R = 3 ÷ 0.015 = 200 Ω.
Check: 200 × 0.015 = 3 V.
Question 5: Explain the role of the resistor in Question 4 (2 marks).
Answer
The resistor limits the current, so the LED receives a safe 15 mA. Without it, the current would rise too high and the LED could be damaged.
Question 6: Two identical 4 Ω lamps are connected to an 8 V ideal battery, first in series and then in parallel. Compare the total current (4 marks).
Answer
Series: total resistance = 4 + 4 = 8 Ω, so current = 8 ÷ 8 = 1 A.
Parallel: each branch carries 8 ÷ 4 = 2 A, so the total is 2 + 2 = 4 A.
The parallel arrangement draws four times the current, because each lamp receives the full 8 V instead of sharing it.
If you got these wrong
- Questions 1 and 2: review tracing a circuit on paper.
- Questions 3 and 4: review checking units and assumptions.
- Question 5: review explaining the role of labelled components.
- Question 6: review comparing two circuit diagrams fairly.
For a teacher to go through your attempts, see online one-to-one Electrical and Electronic Engineering Studies tuition.