Answer
Please see the work below.
Work Step by Step
(a) We know that
$\epsilon=-NA(\frac{\Delta B}{\Delta t})$
$\epsilon=-N(\pi r^2)(\frac{\Delta B}{\Delta t})$
We plug in the known values to obtain:
$\epsilon=-(155)(\frac{\pi(0.0375m}{4})^2)(0)$
$\epsilon=0V $
(b) As $\epsilon=-N(\pi r^2)(\frac{\Delta B}{\Delta t})$
We plug in the known values to obtain:
$\epsilon=(-155)(\pi\frac{(0.0375m)^2}{4})(\frac{-0.01T-0.02T}{5\times 10^{-3}s})$
$\epsilon=1.0V $
(c) At time $ t=15ms $ the induced emf is zero because the rate of change of the magnetic field is zero.
As $\epsilon=-N(\pi r^2)(\frac{\Delta B}{\Delta t})$
We plug in the known values to obtain:
$\epsilon=-(155)\frac{\pi(0.0375m)^2}{4}(0)$
$\epsilon=0V $
(d) We know that
$\epsilon=-N(\pi r^2)(\frac{\Delta B}{\Delta t})$
We plug in the known values to obtain:
$\epsilon=-(155)(\frac{\pi(0.375m)^2}{4})(\frac{0.01T-(-0.01T)}{10\times 10^{-3}s})$
$\epsilon=-0.3V $
