Answer
Choice C.
Work Step by Step
The magnitude of the induced emf is given by Faraday’s Law.
$$\epsilon=\frac{d\Phi_B}{dt}= A\frac{dB_{av}}{dt}$$
The latter quantity is the slope of a B-versus t graph. The induced emf, and thus the current, is greatest when the slope of a B vs. t is steepest.
The graph in the introduction rises to 4 T in about 0.15 ms.
In Figure P29.73, both graph A and graph B rise to 4 T in less than 0.1 ms. They have steeper slopes.
