Answer:
induced emf = Â 28.65 mV
Explanation:
given data
diameter = 7.3 cm
magnetic field = 0.61
time period = 0.13 s
to find out
magnitude of the induced emf
solution
we know radius is diameter / 2
radius = 7.3 / 2
radius = 3.65 m
so induced emf is dπ/dt  = Adb/dt
induced emf =  A × ΔB / Δt
induced emf =  πr² × ΔB / Δt
induced emf =  π (0..65)² × ( 0.61 - (-0.28))  / 0.13
induced emf = Â 0.0286538 V
so induced emf = Â 28.65 mV