Question

In the circuit given below, identify the lamp (L1, L2, L3 or L4) whose failure would not interrupt the power supply to the other lamps.

• A. L1
• B. L2
• C. L3
• D. L4

Hint:

In a combined series-parallel circuit, the failure of a component in a parallel branch only affects that branch. The failure of a component in the main series part affects the entire circuit.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
We need to analyze the given electrical circuit and determine which single lamp's failure (becoming an open circuit) would still allow current to flow to the other lamps in the circuit.
Step 2: Detailed Explanation:
Let's analyze the circuit configuration:
- Lamp L1 is in series with the rest of the circuit. - The rest of the circuit consists of two parallel branches. - Branch 1 contains only lamp L2. - Branch 2 contains lamps L3 and L4 connected in series.
Now let's consider the failure of each lamp one by one:
- If L1 fails: It is in series with the entire combination. An open circuit at L1 would break the main path for the current from the power supply. No current would flow to L2, L3, or L4. All other lamps would go out.
- If L2 fails: The parallel branch containing L2 would become an open circuit. Current would stop flowing through this branch. However, the main circuit is still complete. Current would flow from the supply, through L1, and then through the other parallel branch containing L3 and L4. So, L1, L3, and L4 would remain lit. The power supply to these lamps is not interrupted.
- If L3 fails: The series combination of L3 and L4 would become an open circuit. No current would flow through this branch, so L4 would also go out. However, current would still flow from the supply, through L1, and then through the parallel branch containing L2. So, L1 and L2 would remain lit. The power supply to L4 is interrupted.
- If L4 fails: This is similar to L3 failing. The series branch containing L3 and L4 would open. L3 would go out. Current would still flow through L1 and L2. The power supply to L3 is interrupted.
Step 3: Final Answer:
The failure of L2 is the only case where all the other lamps (L1, L3, and L4) continue to receive power and stay lit. Therefore, the failure of L2 does not interrupt the power supply to the other lamps.