A bolt of lightning strikes 100 m from a moonshiner’s still. There are 8 loops i

Question

A bolt of lightning strikes 100 m from a moonshiner’s still. There are 8 loops in the “condensing pipe” of the still. Each loop has a radius of 0.20 m. The length of the coiled part of the condensing pipe is 1.20 m. Treat lightning bolt as if it were a long vertical wire conducting electrons from cloud to ground. Assume the current in the lightning bolt drops from 5.00 x 106 A to zero in 10.0 microseconds.

A) Draw in the magnetic field due to the lightning bolt into the leftmost picture.

B) The arrow in the rightmost illustration represents the magnetic field of the lightning bolt. If the magnetic field of the lighting strike threads through the condensing pipe parallel to its long axis (as in the picture to the right_ calculate the emf ? generated in the condensing pipe.

C) Assuming the still has a resistance of 2000 ? what is the induced current?

D) Carefully draw in the rightmost picture the induced current in the condensing pipe.

Note: Please show your work, so I can compare and comprehend my answers. Thanks!

Explanation / Answer

A) Lightning bolt is conducting electrons from cloud to the ground means it is flowing current from ground to the cloud.

Using right hand rule we can say that magnetic fields are in the leftside picture from left to right.

B) If we have to find initial magnetic field due to lightning bolt

Bi = 0*I/4r = (8.85*10^-12*5*10^6)/(4*3.14*100) = 3.5*10^-8 T

Bf = 0 T

t = 10*10^-3 s

d/dt = (3.5*10^-8 – 0)/( 10*10^-3) = 3.5*10^-6 T/s

By Faraday’s law,

|e| = Nd/dt = NA*dB/dt = 8*3.14*0.20^2*3.5*10^-6 = 3.5*10^-6 volt

C) I = |e|/R = (3.5*10^-6)/2000 = 1.75*10^-9 = 1.75nA

D) By Lenz law induced magnetic field will oppose the external magnetic field which is decreasing, thus south pole induced magnetic field will be directed to left. Again right hand rule we can show that current in the loops flows anticlockwise.

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