A bar magnet is moved along the common axis of a circular copper coil that is…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A bar magnet is moved along the common axis of a circular copper coil that is connected to a sensitive galvanometer. The coil is kept fixed on a non-magnetic stand.
Answer the following questions in the order given and give clear justification in each case.
(i) State Lenz’s law as applicable to electromagnetic induction.
(ii) If the north pole of the magnet is pushed steadily towards the centre of the coil, identify the polarity produced at the face of the coil nearest to the magnet. Hence indicate the direction of the induced current when viewed from the magnet’s side.
(iii) The magnet is now quickly withdrawn along the same line. Determine the new polarity at the same face of the coil and the corresponding direction of the induced current.
(iv) Explain, with the help of energy considerations, why the directions obtained in parts (ii) and (iii) must be as stated by you.