Answer
280 T/s
Work Step by Step
The magnitude of the average induced emf is calculated using equation 21–2b. The flux changes because the magnetic field changes.
$$|\epsilon|=N\frac{\Delta \Phi_B}{\Delta t}=N\frac{A \Delta B}{\Delta t}$$
Solve for the rate of change of magnetic field.
$$\frac{\Delta B}{\Delta t}=\frac{\epsilon}{NA} $$
$$=\frac{120V}{(35)\pi (6.25\times10^{-2}m)^2}=280T/s$$
