## PSN-L Email List Message

Subject: Re: The Magic
From: ChrisAtUpw@.......
Date: Sat, 7 Jul 2007 18:53:23 EDT

```In a message dated 2007/07/07, tchannel1@............ writes:

> She is often at the computer, by the Sensor, when people visit the museum.
> One question she gets, is "How does it work"  She understands how it is
> built and all the parts, but when the questions focuses on the magnetic field and
> the coil, she can only discuss their interaction, creates a current, like
> "Magic"

Hi Ted,

Movement of a coil in a magnetic changing field does not produce a
current, but a voltage across the ends of the coil. This voltage is proportional
to the number of turns, to the area of the coil and to the rate of change of
the field.
A current flowing in a conductor has a ring magnetic field assocciated
with it. If you use a circular solenoid, the turns add up to give an axial
agnetic field.

I use a school demo system having quad NdFeB magnets on two parallel mild
steel backplates. I use a relay coil on a handle connected to back to back
red and green LEDs. You move the coil one way and the red LED lights, the other
way and the green LED lights. If you move the coil more rapidly, the LEDs glow
a lot brighter. Why not make up a similar model for the museum?

>  I have seen a formula explaining the three factors, The Field, The Coil,
> and The Velocity..........
> Could someone tell me or direct me to an explanation of "The Magic"  which
> is really the basic for this type of sensor.

Regards,

Chris Chapman
In a me=
ssage dated 2007/07/07, tchannel1@............ writes:

She is often at the computer, b=
y the Sensor, when people visit the museum.  One question she gets, is=20=
"How does it work"  She understands how it is built and all the parts,=20=
but when the questions focuses on the magnetic field and the coil, she can o=
nly discuss their interaction, creates a current, like "Magic"

Hi Ted,

Movement of a coil in a magnetic changi=
ng field does not produce a current, but a voltage across the ends of the co=
il. This voltage is proportional to the number of turns, to the area of the=20=
coil and to the rate of change of the field.
A current flowing in a conductor has a=20=
ring magnetic field assocciated with it. If you use a circular solenoid, the=
turns add up to give an axial agnetic field.

I use a school demo system having quad NdFeB magnets=20=
on two parallel mild steel backplates. I use a relay coil on a handle connec=
ted to back to back red and green LEDs. You move the coil one way and the re=
d LED lights, the other way and the green LED lights. If you move the coil m=
ore rapidly, the LEDs glow a lot brighter. Why not make up a similar model f=
or the museum?

I have seen a formula explain=
ing the three factors, The Field, The Coil, and The Velocity..........
Could someone tell me or direct me to an explanation of "The Magic"  w=
hich is really the basic for this type of sensor.

Regards,

Chris Chapman
```