Question

A fixed 12.1-cm-diameter wire coil is perpendicular to a magnetic field 0.71 T pointing up. In 0.14 s , the field is changed to 0.15 T pointing down.

What is the average induced emf in the coil?

Answer 1

According to faraday's law, induced EMF= df/dt, where f is magnetic flux and t is time.

Also, f=BA, where B is magnetic field and A is area.

So, EMF= d(BA)/dt = A dB/dt (since area is constant)

Area of circular coil=d2/4 , where d is diameter. Here, d = 12.1 cm =0.121 m. So, area=*0.1212/4=0.011499 m2

Now, initially, magnetic field was 0.71T pointing upwards, and finally, magnetic field was 0.15 T pointing downward. So, change in magnetic field= 0.71-(-0.15) =0.86 T.

Also, time=0.14 s.

So, dB/dt= (change in magnetic field)/time= 0.86/0.14=6.142857 T/s

So,EMF = A dB/dt = 0.011499*6.142857 = 0.070637 V = 0.071 V approximately.