A neon lamp tester contains a resistor and a small neon lamp. It works by creating a circuit through the body of the person holding it to the ground. - The live wire in an AC mains supply carries the alternating voltage relative to the neutral wire and ground (typically 220-240V in many countries). When the tester touches the live wire, there is a large potential difference between the live wire and the ground (via the person holding the tester). This voltage is sufficient to drive a tiny current (limited by the resistor in the tester) through the neon lamp and the person's body to the ground, causing the lamp to glow. - The neutral wire is connected to the ground at the power source (substation or main distribution panel). Therefore, the neutral wire is ideally at or very close to ground potential (zero voltage relative to ground). When the tester touches the neutral wire, the potential difference between the neutral wire and the ground (via the person) is minimal. This voltage difference is not sufficient to ionize the gas in the neon lamp and make it glow.
In our homes, a tester glows when it touches the live terminal of AC mains but does not glow when it touches neutral terminal. The reason for this is
Asked in KPSC KAS Prelims 2014 · Topic: Electric Current (Ohm's Law, resistance, resistivity, and conductivity)
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Answer: C. the neutral terminal is at the same voltage as the ground.
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