Key Idea According to Faraday's second law of electromagnetic induction the induced emf is given by rate of change of magnetic flux linked with the circuit. Here, B=0.04 T and dt−dr=2mms−1 Induced emf, e=dt−dϕ=dt−BdA=−Bdtd(πr2) =−Bπ2rdtdr Now, if r=2 cm e=−0.04×π×2×2×10−2×2×10−3=3.2πμV