Currents in dc transmission lines can be 100 A or more. Some people have expressed concern that the electromagnetic fields (EMFs) from such lines near their homes could cause health dangers.

Part A

For a line with current 180 A and at a height of 8.0 m above the ground, what magnetic field does the line produce at ground level? Express your answer in teslas.

B=T

Part B

What magnetic field does the line produce at ground level as a percent of the earth's magnetic field, which is 0.50 gauss.

B/Be=%

Explanation:

Current in distribution line

I=100A

EMF at such height from the earth can cause hazard

a. To know how strong the magnetic field are at a height of 8m above the earth

And the line current is 180A

I=180A

Magnetic field is given as

B= μoI /2πa

μo = permeability of free space

I = magnitude of current in the wire

a = perpendicular distance between point P and the straight current carrying conductor.

a=8m from earth

μo is a constant and it value is

μo=4π×10^-7 H/m

Then,

B=μoI /2πa

B= 4π×10^-7 × 180 / (2π ×8)

B= 4.5×10^-6 T

b. Earth magnetic flux is 0.5gauss

Note, 1 gauss = 10^-4 Telsa

Therefore, the magnetic field on earth becomes

Be=0.5gauss = 0.5 × 10^-4

Be=5×10^-5

Then, the percentage of magnetic field due to magnetic on earth is

B/Be ×100

(4.5×10^-6) / (5×10^-5) ×100

0.09×100

9%

The magnetic field produce a 9% percentage on the ground level

the answer is 100. i just did this lesson and got a 100% on it. : )

-fishtank