Example 88: Several lights in Xiaogang's home suddenly went out, check that the fuse was not blown off, and when using electric pen to measure the circuits everywhere, the neon tube glowed. He made the following four judgments on the fault, the correct one is ().
A. All light bulbs are burnt out
B. Neutral line into the house is broken
C. Short circuit occurs in the indoor line
D. Fire line into the house is broken
Analysis: 1 From the question, it can be seen that the fuse of
1.1 has not been burned out, and there will be circuit breaking in the circuit, as shown in the figure:
1.2 When using a test pen to test the circuits in various places, the neon tubes are luminous, indicating that these places are connected to the live wire of the power supply. From the above inference, we can see that options A and D are impossible.
1.3 Because several lights suddenly went out, it indicates that the current cannot pass through the circuit, and the circuit may be broken somewhere. The result of this circuit breaker is that all the lights are turned off. Then the circuit breaker must be on the main road, that is, on the entrance line.
1.4 It is known from the question that when measuring with an electric pen, the neon tubes are illuminated, which means that the live wire circuit in the home is unobstructed and there is no circuit breaker. Therefore, the circuit breaker must occur on the neutral line in the home, so option B is correct.
1.5 In addition, if a short circuit occurs, the current will be too high and the fuse will be immediately blown off, causing the incoming live line to be broken. In this way, when the electric pen tests the circuits everywhere, the neon tube will not emit light, so option C is wrong.
To sum up, correct answer: B.
2 summary: Draw a simplified form of the diagram home circuit , which can visualize the problem. Then imagine that the neon tubes in the test pen test diagram are emitted and the current flows through, and determine the fault.
