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## Homework Statement

At one instant, the two conductors in a long

household extension cord carry equal 1.61 A

currents in opposite directions.

Find the magnetic ﬁeld 2.4 cm away from

the middle of the straight cord, in the plane of

the two wires, if the centers of the two wires

are 2.92 mm apart.

Answer in units of µT.

At what distance is it one tenth as large?

Answer in units of cm.

The center wire in a coaxial cable carries current 1.61 A in one direction, and the sheath

around it carries current 1.61 A in the opposite direction. Consider a point P outside of

the sheath at a distance r from the middle of

the center wire. Assume the center wire without any sheath would create a magnetic ﬁeld

of B at the point P.

What magnetic ﬁeld does the cable and

sheath create at point P?

1. r B

2. None of these

3. More information is needed.

4. 2 B

5. 0.5√r B

6.√r B

7. 0.1 B

8.B/r

9. zero

## Homework Equations

F = (mu/2(PI)*d)*(L)*(I1)*(I2)

B = (mu/2(PI))*(I/(d))

## The Attempt at a Solution

I don't know how to do this problem at all, the equations I have don't even make since using because it is asking for the magnetic field. If I were to do the magnetic fields separately and add them would that give me the correct value? The only thing that matters since they are close together is the force that acts upon them correct? So if I were to do the wires separately:

d1 = 2.4cm - 2.92mm

d2 = 2.4cm + 2.92mm

B1 = (mu/2(PI))*(I/d1)

B2 = (mu/2(PI))*(I/d2)

B(at point A) = B1 + B2

This doesn't seem correct to me( I am studying for a test and this was a practice problem he gave us, hence I don't have the correct answer), is there any place I am going wrong about this?

On the third part I have no idea what it is asking at all...

Using the right hand rule I know that one of the magnetic fields is going into point A and one is going out of point A so would I subtract one from the other? I am lost, help is greatly appreciated.

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