Question

A lightning bolt may carry a current of 1.00 × 10⁴ A for a short time. What is the resulting magnetic field 190 m from the bolt in μT? Suppose that the bolt extends far above and below the point of observation.  

(1) 10.5 

(2) 20.00 

(3) 120 

(4) 66.1 

(5) none of these  

Answer 1

Correct option: (1) 10.5

Explanation

The B field at a distance r from a long straight wire, which is what the lightning bolt essentially is, is given by B μoi / 2πr = ( 2x 10^-7) (10⁴)/ 190 = 1.05 x 10^-5 T =10.5 μT.