Advanced Science Primary 5 Systems

Study the circuit. Which switch must be CLOSED for Bulb X to light up, while Bulb Y remains unlit?

A Close S1 and S2
B Close S2 and S3
C Close S1 only
D Close S1 and S3
Show Worked Solution

Worked Solution

Step 1: S1 is on the main path. It must be closed for any current to flow from the battery. Step 2: Bulb X is on the top branch, controlled by S2. So, S2 must be closed. Step 3: Bulb Y is on the bottom branch, controlled by S3. To keep Y unlit, S3 must remain open. Step 4: Therefore, close S1 and S2.

Correct answer: Close S1 and S2

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