Question

A student performs an experiment to study the magnetic effect of current around a current carrying straight conductor. He reports that:
(i) the direction of deflection of the north pole of a compass needle kept at a given point near the conductor remains unaffected even when the terminals of the battery sending current in the wire are interchanged.
(ii) for a given battery, the degree of deflection of a N-pole decreases when the compass is kept at a point farther away from the conductor.
Which of the above observations of the student is incorrect and why?

Answer 1

Observation (i) is wrong because the deflection of a compass needle by the current-carrying straight conductor depends upon the magnetic field around it. So, it is the magnetic field produced by the current-carrying conductor which deflects the compass needle. Therefore, if we reverse the direction of current flowing in the conductor then the deflection of the magnetic needle would also be in the opposite direction.

Observation (ii) is correct because magnetic field strength decreases as we move away from the conductor. So, the deflection would decrease too.