Question

2) A square coil with an initial area of 11 m², is wrapped once and is placed in the x-y plane a magnetic field in the -z direction of 0.5 T. The area of the coil is changed in a time of 0.8 seconds. The resistance of the square coil is 9 Ohms, and when the areas is changed, an induced current of 0.4 amps running clockwise around the coil. What is the final area of the coil in m²?  

Answer 1

Emf induced is given by: change in flux/time taken

Change in flux =   where B is magnetic field and and are final and initial areas respectively.

Current = Induced EMF/Resistance

On solving above equation, Change in area is 5.76.
Since, the induced current is clockwise, direction of magnetic field due to it is along -z. Therefore, the area must be reducing as per Lenz's law which states the current is induced in such a way so as to oppose any flux change.

Therefore, final area = 11 - 5.76 = 5.24m2