This following applet is [b] Current Loop in magnetic field (How motor works!)[/b]
Created by prof Hwang Modified by Ahmed
Original project [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=912.0]Current Loop in magnetic field (How motor works!)[/url]

This simulation shows a current loop in uniform magnetic field.
The brown arrows show the force due to magnetic field on the loop. $\vec{F}= q \vec{v} \times \vec{B} or \vec{F}= I \int d\vec{\ell} \times \vec{B}$
The magnetic field in in the +Z direction if Bz>0.
Then ,torque for the loop is calculated from definition $\vec{\tau}=\vec{r}\times\vec{F}$

Because the current flow in the same counter-clockwise direction.
The force on the loop change sign during each helf cycle.
If we current reverse direction during each helf cycle, the following device can turn into a motor.
A voltage source is needed in the loop to drive the current.

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