Advanced Science Primary 5 Systems

Study the mixed circuit diagram below. Switch S1 is closed while Switch S2 is left open. Which bulb(s) will light up?

A Bulb B2 only
B Bulb B1 only
C Neither B1 nor B2
D Both B1 and B2
Show Worked Solution

Worked Solution

Step 1: Switch S1 is on the main series path. Because it is closed, current can flow from the battery to the parallel branches. Step 2: The top branch with Bulb B1 has no open switches, so it forms a closed circuit. B1 lights up. Step 3: The bottom branch has Switch S2, which is open. Current cannot flow through B2. Step 4: Therefore, only B1 lights up.

Correct answer: Bulb B1 only

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