Question

A circular loop in the plane of the paper lies in a 0.78 T magnetic field pointing into the paper.
If the loop's diameter changes from 17.8 cm to 6.4 cm in 0.22 s, what is the direction of the induced current?
What is the magnitude of the average induced emf?
If the coil resistance is 2.9 Ω, what is the average induced current?

Answer 1

The induced current will be in the dorection that increases the flux through the loop.

The magnitude of the induced emf is
d(Phi)/dt = B*dA/dt
= 0.78T*(pi/4)[(.178^2 -.064)^2]/0.22s
= 0.077 V

Divide by 2.9 ohms for the induced current.

Answer 2

Thank you!