In a standard Post Office Box experiment, which of the following statements is correct?

The null point reading implies the position of jockey for which reading of galvanometer is zero.
The null point reading means consecutive readings at which the galvanometer deflects in the opposite direction
The key connected to Galvanometer is switched on after switching on the key connected to battery.
The key connected to Galvanometer is switched on after switching off the key connected to battery.

Correct answer: The key connected to Galvanometer is switched on after switching on the key connected to battery.

Solution

Standard laboratory procedure for Post Office Box: first close the battery key, then press the galvanometer key. This protects the sensitive galvanometer from inductive transients. Option C correctly states this sequence.

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