# Homework Help: Magnitude of magnetic force

1. Jun 28, 2012

### swankymotor16

A rectangular loop of wire measures 1.0 m by 1.0 cm. If a 7.0-A current flows through the wire, what is the magnitude of the magnetic force on the centermost 1.0-cm segment of the 1.0-m side of the loop?

Fm = ILBsin of angle

Fm = Magnetic force

I= Electric current

L= Length of conductor

B= magnetic field intensity

B= (4∏x10^-7)(7.0A)/(2∏)(0.01m) = 1.4x10^-8

Fm= (7.0A)(1.0m)(1.4x10^-8)= 9.8x10_8

2. Jun 28, 2012

### collinsmark

(Don't forget your units.)

That's a pretty good approximation. The formula which you used for B, can be derived using Ampere's law (Edit: or you could use calculus + Biot-Savart law), is only really valid for an infinitely long wire. But since we're dealing with a distance to the wire being much, much shorter than the wire itself, it makes a fine approximation. (If you wanted to get more precise, you'd have some calculus to do. But I'm guessing the approximation is fine for this problem.)
(Again, don't forget your units.)

Hold on, the problem statement said,
"magnetic force on the centermost 1.0-cm segment"​
It's not asking for the force on the entire 1 meter wire. It's just asking for a force on the center-most 1 centimeter segment of the 1 m wire.

Last edited: Jun 28, 2012