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A tester has a bulb that does NOT glow when dipped in a particular liquid. Which of the following could account for this? (I) The liquid is a poor conductor. (II) The current is so small that it does not heat the bulb's filament enough. (III) The bulb is fused / cells are dead.

AAny of I, II or III
BOnly III
COnly I
DOnly II
Answer & Solution
Correct answer: A. Any of I, II or III
All three are valid possibilities. Before concluding the liquid is non-conducting, the tester should be 'self-checked' by short-circuiting its leads. If the bulb glows then, the tester works — and the non-glow with the liquid is genuinely about the liquid (poor conductor or current too small for the bulb). If not, the bulb or cells are at fault.
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