A wire of irregular shape in figure (a) and a circular loop of wire in figure (b) are placed in different uniform magnetic fields as shown in the figures below. In figure (a), the magnetic field is perpendicular into the plane. In figure (b), the magnetic field is perpendicular out of the plane.
The wire in figure (a) is turning into a circular loop and that in figure (b) into a narrow straight wire. The direction of induced current will be ________________.
Fill in the blank with the correct answer from the options given below.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → anticlockwise in both (a) and (b)
By Lenz's law, the induced current flows so as to oppose the change in magnetic flux through the loop. The field is uniform, so the flux \( \Phi = BA \) changes only because the enclosed area changes.
Figure (a): for a given length of wire, a circle encloses the largest area. As the irregular wire opens out into a circle, the enclosed area grows, so the flux into the plane increases. The induced current must set up a field out of the plane inside the loop, and a current that gives an outward field inside a loop flows anticlockwise.
Figure (b): as the circular loop is squeezed into a narrow straight wire, the enclosed area falls towards zero, so the flux out of the plane decreases. The induced current must make up for this loss by producing a field out of the plane inside the loop, so again it flows anticlockwise.
NCERT (2026-27):
Lenz’s Law and Conservation of Energy – “… The statement of the law is: The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it.”
Exercises – “… 6.2 Use Lenz’s law to determine the direction of induced current in the situations described by Fig. 6.16: (a) A wire of irregular shape turning into a circular shape; (b) A circular loop being deformed into a narrow straight wire.”