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Question:

In a coil of resistance 100Ω, a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude of change in flux through the coil is:

200Wb

225Wb

275Wb

250Wb

Solution:

Induced emf E=dΦ/dt ∴dΦ=Edt=iRdt
ΔΦ=∫iRdt
From the graph, current is given by i= -60t+10
ΔΦ=∫₀⁰·⁵(-60t+10)×100dt = -6000[t²/2]₀⁰·⁵ + 1000[t]₀⁰·⁵ = -6000×0.25 + 1000×0.5 = 250 Wb