A lightning bold strikes the ground 200m from a 100-turn coil. Supposed that the

Question

A lightning bold strikes the ground 200m from a 100-turn coil. Supposed that the radius of the coil is .8m and that the current carried by the lightning bolt is 6.0 MA and falls to zero in 10.5 ms. What is the induced emf in the coil if it is oriented with its normal along the magnetic field direction? If the wire has a cross sectional area of 7.85 X 10-7 m2 (diameter of wire is 1 mm), and it is made out of copper                            ( = 1.7 X 10-8 m), what is the magnitude and direction of the induced current in the wire?

Explanation / Answer

the magnitude of magnetic field at the time when the lighting first strikes the ground. B=I*muy0/((2pi*R)*2)=I*muy0/4piR=3e-3(T). so the change in magnetic flux. ?O=3e-3*100*0.8^2*pi=0.603 so the change rate = inducted emf. ?O/?t=-U=57.4(V) the total length of the wire. L=100*0.8*2pi=503(m). resistance R=p*L/S=10.9(ohm) so I=U/R=5.3(A) ---

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