### Re: What is Fleming's Left hand and right hand rule, and what do they do

Date: Mon Jan 22 19:47:19 2001
Posted By: Drew Procyk, Staff, Physicist, Beam Technology R&D, FEI Company
Area of science: Physics
ID: 979396870.Ph
Message:
```
Hello Marianne,
Hopefully I can shed some light on the right and left hand rules.  First,
who _was_ this Fleming guy?  Sir John Ambrose Fleming lived 1849-1945 in
England and was an electrical engineer.  Most of his work was in electric
lighting and telegraphs.  He developed some of the first electric ship
lights, but he is most noted for developing the vacuum diode- a device
that converts an alternating current radio signal to a direct current that
one of the on-line encyclopedias such as www.britannica.com.

Now on with the right and left hand rules.  They are handy ways to
remember the relationship between magnetic field, current, and the
resulting force on the conductor (or motion if it's allowed to move).
Finger positions: for the right-hand rule, if you hold your right hand so
that you point your index finger to something in front of you, have your
thumb pointing toward the ceiling, and second (middle) finger to the left
so that each finger is perpendicular to the other two.  The same finger
finger positions on the left hand are used for the left-hand rule.

An electric motor is very simply a loop or coil of wire that is free to
rotate in a magnetic field.  When there is a current in the wire, a
magnetic field is generated which will want to align itself with the
external magnetic field.  This causes the loop to want to rotate.  For
this we use the LEFT hand rule to determine the direction of the force on
the wire and hence which way the motor will turn.  If your fore finger
points along the magnetic field and the central finger along the direction
of the current, then the thumb points along the direction of motion of the
conductor.

A dynamo or generator is essentially a type of electric motor which has
permanent magnets in it to provide the magnetic field.  Instead of
supplying a current to the coil and getting rotational motion of the shaft
in return, you supply rotational motion and get a current in return.  In
this case the RIGHT hand rule can be used to determine the direction of
the current flow in the wire loop.  If your fore finger points along the
magnetic field and the thumb points along the direction of motion of
conductor, then the central finger would give us the direction of the
induced current.

I checked what my fingers represented in the CRC Handbook of Chemistry and
Physics to make sure I was right (or left?)

Good luck,
Drew

```

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