WEBVTT - How does a Crooke's radiometer work?

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<v Speaker 1>Brand with today's question, how does a Crooks radiometer work?

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<v Speaker 1>A Crooks radiometer has four veins suspended inside a glass bulb.

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<v Speaker 1>The veins are black on one side and silver on

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<v Speaker 1>the other. Inside the bulb, there's a good vacuum. When

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<v Speaker 1>you shine a bright light on the veins in a radiometer,

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<v Speaker 1>they spin. In bright sunlight, they can spin at several

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<v Speaker 1>thousand rotations per minute. The vacuum is important to the

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<v Speaker 1>radiometer's success. If there's no vacuum, that is, if the

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<v Speaker 1>bulb is full of air, the veins don't spin because

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<v Speaker 1>there's too much drag. If there's a near perfect vacuum,

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<v Speaker 1>the veins do not spin unless they are held in

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<v Speaker 1>an absolutely frictionless way. If the veins have a frictionless

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<v Speaker 1>support and the vacuum is complete, then photons bouncing off

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<v Speaker 1>the silver side of the veins push the veins, causing

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<v Speaker 1>them to rotate. However, this force is exceedingly small. If

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<v Speaker 1>there's a good but incomplete vacuum, then a different effect

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<v Speaker 1>called thermal transporation occurs along the edges of the veins.

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<v Speaker 1>The effect looks as though the light is pushing against

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<v Speaker 1>the black faces. The black side of the veins moves

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<v Speaker 1>away from the light. For more on this and thousands

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<v Speaker 1>Jack Dreads is the online shopping destination for dudes. Everything

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