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Solve: Magnetic Field on a Compass

Question: A power line is 3.5m off the ground and is carrying 75 amps. A man standing under the power line is holding a compass 1.25m off the ground.

1) How large is the magnetic field produced on the compass by the power line?
2) If the power line runs east and west, how does its magnetic field affect the direction in which the compass points?
3) If the power line runs north-south, how does the magnitic field affect the direction in which the compass points?

Solution Preview

1.)
Because,
Distance/height of the power line from the ground = 3.5 m
Distance/height of the observer from the ground = 1.25 m
Hence,
Distance of the observer from the power line (r)= 3.5-1.25 = 2.25 m
current in the power line (I)= 75 A
Because, magnetic field due to current carrying conductor:
B = k*2*I/r
Here, k= mu_o/4pi = 10^(-7) N/A^2
=> B = 10^(-7)*2*75/2.25 = 6.67*10^(-6) T = 6.67*10^(-2) Gauss
(because 1 Gauss = 10^(-4) T)
=> B = 0.067 Gauss (Answer) ...

Solution Summary

In about 340 words, including explanations and the appropriate calculations, the details for these three problems focused on the concept of magnetism are solved. A jpg document is also attached which corresponds to question two.

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