A long, straight telephone cable contains six wires, each carrying a current of

Question

A long, straight telephone cable contains six wires, each carrying a current of 0.300 A . The distances between wires can be neglected.

Part A

If the currents in all six wires are in the same direction, what is the magnitude of the magnetic field 2.80 m from the cable?

B1 = ____ T

Part B

If four wires carry currents in one direction and the other two carry currents in the opposite direction, what is the magnitude of the field 2.80 m from the cable?

B2 = ____ T

Part C

Home circuit breakers typically have current capacities of around 8.0 A .

How large a magnetic field would such a current produce 5.6 cm from a long wire?

Express your answer using two significant figures.

B = ____ T

Explanation / Answer

magnetic field at a diatance r from a large current carrying current = B = uo*i/(2*pi*r)

part(A)

B1 = (6*uo*I)/(2*pi*r)

B1 = (6*4*3.14*10^-7*0.3)/(2*3.14*2.8) = 1.28*10^-7 T

+++++++++++++++

B2 = (4-2)*(uo*I)/(2*pi*r)

B2 = (2*uo*I)/(2*pi*r)

B2 = (2*4*3.14*10^-7*0.3)/(2*3.14*2.8) = 4.28*10^-8 T

+++++++++++

part(C)

B = uo*i/2*pi*r

B = (4*3.14*10-7*8)/(2*3.14*0.056) = 198 T

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