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deborahcurrie
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Homework Statement
A researcher would like to perform an experiment in a zero magnetic field, which means that the field of the Earth must be cancelled. Suppose the experiment is done inside a solenoid of diameter 1.0{\rm m} , length 5.0{\rm m} , with a total of 9000 turns of wire. The solenoid is oriented to produce a field that opposes and exactly cancels the field of the earth.
What current is needed in the solenoid's wires?
Homework Equations
We use this for B=μ0*I*(N/L) for solenoids.
Bearth=5E-5T
μ0=1.257E-6
N=9000
L=5.0 m
The Attempt at a Solution
I=(B*L)/μu0*N)=(5E-5*5)/(9000*5) = 0.02209=2.2E-2
Mastering Physics says this is incorrect. What did I miss?