Question

A) Use Lenz’s law to determine the direction of induced current in a wire of irregular shape turning into a circular shape.


B) Use Lenz’s law to determine the direction of induced current in the situation described by Fig. A circular loop being deformed into a narrow straight wire.

Answer 1

A) The wire is expanding to form a circle and magnetic field is acting in the normal to the plane of loop away from the reader. Since, area of loop increases, the magnetic flux linked also increases. The direction of induced current should be such that it will produce magnetic field in opposite direction (normal to the plane and towards the reader).
Hence induced current will be flowing in anticlockwise direction in the loop along adcb (flux through the surface increases during shape change, so induced current produces opposing flux).
Final answer: Along adcb

B) When circular loop is transformed into a narrow straight wire, then the area of the loop will be decreasing with time, leading to decrease in magnetic flux. The induced current should be such that it opposes the decrease in the magnetic flux. Therefore, the current flow will be along a' d' c' b' which produces the induced magnetic field normal to the plane of loop and towards the reader.
Final answer: Along a'd'c'b'