At the equator, the earth\'s field is essentially horizontal; near the north pol

Question

At the equator, the earth's field is essentially horizontal; near the north pole, it is nearly vertical. In between, the angle varies. As you move farther north, the dip angle, the angle of the earth's field below horizontal, steadily increases. Green turtles seem to use this dip angle to determine their latitude. Suppose you are a researcher wanting to test this idea. You have gathered green turtle hatchlings from a beach where the magnetic field strength is 50 ?T and the dip angle is 56 degree. You then put the turtles in a 1.6 m diameter circular tank and monitor the direction in which they swim as you vary the magnetic field in the tank. You change the field by passing a current through a 150-turn horizontal coil wrapped around the tank. This creates a field that adds to that of the earth.

What current should you pass through the coil, to produce a net field in the center of the tank that has a dip angle of 62 degree? Express your answer to two significant figures and include the appropriate units.

Please show detailed solution. Thank you!

Explanation / Answer

apply for Dip magnetic field Bnet = B tan theta

Bnet = 50uT * tan62

Bnet = 1.88uT

now use B = uoNI/2R

so current I = 2BR/uoN

i = 2* 1.88*10^-6 * 0.8 /(4pi*10^-7 * 150)

i = 0.0159 A or 16 mA, current must be in clockwise direction to produce fiedl in downward direction

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