Anyone have a Crookes radiometer as a kid?

[oldbrownhat]

My gf & I were talking about cats lounging by the window, absorbing the winter sun and that presumably black cats stay warmer than white ones etc., and I remembered I had one of these when I was a kid. Apparently there is still some uncertainty about what makes it work.

I wondered if it could be developed to generate power, but I'd guess that if so, we'd have heard about it by now,

 

[delcrossv]

I had one. Always enjoyed it.

 

[soFlaNative]

Oh yeah, black warms quicker than white but how that energy transfers into motion is beyond me.
I never knew what the gizmo was called but I like a bit of mystery.

 

[lihpster]

I wondered if it could be developed to generate power, but I'd guess that if so, we'd have heard about it by now,

I can't imagine it would be very efficient as a means of generating power, simply from a physics standpoint. It is basically a temperature differential engine and you have to generate energy to cool or heat one side of the equation, if not both. Small size is easier, the sun or even the heat from your hands can do it, but if you want to generate usable power, size goes up and the necessary energy needed to produce it goes up.
But the real stopping point, I think, is the glass vacuum chamber. By the time you make the engine big enough to generate usable power, the glass dome, which needs to transfer radiant energy, has to be soap bubble thin, relatively speaking. And it has to be strong enough to hold a partial vacuum. I don't know what one of those would cost to make, but I sure wouldn't want to pay it.

 

[DWalt]

They are still available. Not exactly a perpetual motion machine. The key to its operation is that the bulb has to contain a vacuum. The forces of the photons hitting the black vane blade surfaces are so minuscule that the vanes could not overcome the air resistance and could not rotate.

 

[ralph7]

I remember seeing them, and may have even had one.
Don't remember that name for it, though.

 

[2ffat]

I got mine from Edmund Scientific. Kept it for years.

 

[oldbrownhat]

I got mine from Edmund Scientific. Kept it for years.

Edmund Scientific - that's a name that brings back memories!
They're still around, now known as Scientifics Direct, and they still sell the Crookes radiometer. $18.95.

 

[Rudi]

Never had one but remember them.