The following' precautions' were listed by a student in the experiment on study of 'Dependence of current on potential difference'.
(A) Use copper wires as thin as possible for making connections.
(B) All the connections should be kept tight.
(C) The positive and negative terminals of the voltmeter and the ammeter should be correctly connected.
(D) The 'zero error' in the ammeter and the voltmeter should be noted and taken into consideration while recording the measurements.
(E) The 'key' in the circuit, once plugged in, should not be taken out till all the observations have been completed.

The 'precautions' that need to be corrected and revised are:
(1) (A), (C) and (E)
(2) (C) and (E)
(3) (B) and (E)
(4) (A) and (E)

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Solution

The resistance of a wire is inversely proportional to the area of the cross section of the wire. If a thin copper wire will be used in the experiment then it's resistance would be high, which will generate a lot of heat during the experiment and due to that, observations may vary in the experiment and the student may not get the desired results. so, statement A should be revised and corrected.

Also, if the 'Key' will be kept plugged in for a very long time then there will be some heat generations and due to that, the student may not get the desired results. so, statement E should also be revised and corrected.

Hence, the correct answer is option 4.

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