Although the evidence is weak, there has been a concern in recent years over possible health effects from the magnetic fields generated by electric transmission lines. A typical high-voltage transmission line is 20 m above the ground and carries a 200 A current at a potential of 110 kV.
a. What is the magnetic field strength on the ground directly under such a transmission line?
b. What percentage is this of the earth's magnetic field of 50 ?T?

a

The magnetic field strength is  

Explanation:

From the question we are told that

             The  length line   above the ground  is  

              The current of the line is  

              The voltage of the line is

Generally magnetic field strength is mathematically represented as

Where   is the permeability of free space  

Earths magnetic field is approximately given as

   So the percentage would be

                          %            

conservation of mass

mass before something happens = mass afterwards