**The right-hand
rule**

The magnitude of the force
felt by a charge **q** moving with velocity
**v** through a magnetic field
**B** is:

As stated previously, the
direction of the force is perpendicular to both **v**
and **B**. One more thing must be said to define
the direction. For example, if both **v** and
**B** point in the plane of the screen,
**F** could point either into or out of the
screen to be perpendicular to both vectors. The
**flat right-hand rule** is used to determine which of these two
directions for **F** is the correct one.

To find the direction of
**F**,

- Use your RIGHT hand (dropping pencil if necessary).
- Extend the fingers and extend the thumb at right angles to them.
- Make your thumb point in the direction of
**I** or
**q v**.
- Make your fingers point in the direction of
**B**.
- The direction of the force is now given by the direction your palm
would push something.

This version of the right hand rule applies directly to finding the direction
of the force on a segment of wire carrying a current
*I*. It also works to find the direction of the
force on a moving charge; you only have to realize that for a positive
charge *I* points in the direction of
*v*, while for a negative charge,
*v* is opposite to
*I*.

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Examples
Magnetic fields and forces index
**Lecture index*

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