A wire in the form of a circular loop of radius r lies with its plane normal to a magnetic field B. If the wire is pulled to take a square shape in the same plane in time t, the emf induced in the loop is given by
The correct option is D πBr2t(1−π4)
Induced emf (e)=magnetic field×change in areatime
Since the circumference of the circular loop =2πr.
the side of the square loop l=2πr4=πr2. Therefore,
Hence, the correct choice is (d).