Re: [Phys-l] x-ray machine

[chuck britton <cvbritton@embarqmail.com>]

The 'resistance' of a vacuum can be pretty high ;-)

An 'old fashioned' crt color TV set is a rather good x-ray machine.
Maybe 25 kV instead of 60 kV.

The electron beam hits the metal mask that separates the RGB color  
spots on the screen.

Since the early '70's (IIRC) the front glass is heavily laced with Pb  
to shield the viewer.

The current is limited by the circuit that supplies the electrons to  
the cathode.

Ohm's Rule of Thumb is usually applied to devices that are a bit more  
simple that crt circuits.

On Jul 8, 2009, at Jul 8(Wed) 8:20 , Anthony Lapinski wrote:

> I saw a new dentist a few weeks ago. I could easily see the x-ray  
> from the
> chair, and wrote down some information. I often use "real"
> devices/appliances in my classes when discussing electricity, Ohm's  
> Law,
> etc.
>
> x-ray machine:
> 60 kV
> 7 mA
>
> Using Ohm's Law, we get:
>
> R = (60,000 V)/(0.007 A) = 8.57 x 106 ohms
>
> I thought this result was interesting -- either very high or Ohm's Law
> does not apply well in this case. Any ideas?
>
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