Magnetic Forces on Current-Carrying Wires (Conceptual Question) Is answer correct?

1. Feb 3, 2008

predentalgirl1

Magnetic Forces on Current-Carrying Wires (Conceptual Question)....Is answer correct?

Two straight wires are parallel to each other and carry different currents in the same direction. Do they attract or repel each other? How do the magnitudes of these forces on each wire compare?

The formula used to calculate these attractive or repulsive forces is:

F = BIL

F12 = (μ0I1/2πr)I2L2

F12 = (μ0/2πr) I1I2L2

F12 = (4π X 10-7/2πr) I1I2L2

F12 = (2 X 10-7/r) I1I2L2

F12 represents the force on wire 2 caused by its presence in the magnetic field of wire 1

I1 is the current flowing in wire 1

I2 is the current flowing in wire 2

L2 is the length of the current segment of wire 2 in the field of wire 1

r is the distance between the wires

F21 represents the force on wire 1 caused by its presence in the magnetic field of wire 2

F21 = (μ0I2/2πr)I1L1

F21 = (μ0/2πr) I1I2L1

F21 = (4π X 10-7/2πr) I1I2L1

F21 = (2 X 10-7/r) I1I2L1

If two current carrying wires are parallel to each other, their respective magnetic fields either attract or repel each other.

If two parallel wires have currents traveling in the same direction, the magnetic fields generated by those currents between the wires will both point in opposite directions resulting in the wires attracting each other.

If two parallel wires have currents traveling in opposite directions, the magnetic fields generated by those currents between the wires will both point in the same direction, in this case, into the plane of the page. These wires would repel each other.

2. Feb 3, 2008

Kurdt

Staff Emeritus
Thats a very good explanation. So how do the magnitudes compare and do they attract or repel?

3. Feb 3, 2008

predentalgirl1

How do they compare? I'm not sure..

4. Feb 3, 2008

Kurdt

Staff Emeritus
Well you've pretty much worked them out. The magnitude just means the number associated with it and disregarding the direction. What can you say about the two force equations you've derived?

5. Feb 6, 2008

predentalgirl1

Forces are equal (equal magnitude). And parallel currents attract each other.

6. Feb 6, 2008

Kurdt

Staff Emeritus
Very good.