A flat, stationary circular loop of wire of radius \(a\) is placed in a region of uniform magnetic field directed perpendicular to the plane of the loop. The magnitude of the magnetic field decreases exponentially with time according to \(B(t) = B_0 e^{-t/\tau}\), where \(B_0\) and \(\tau\) are positive constants. Which of the following expressions represents the magnitude of the induced electromotive force (EMF) in the loop at time \(t = \tau\)?