# Tag Info

### If I stood next to a piece of metal heated to a million degrees, but in a perfect vacuum, would I feel hot?

I'm more so asking about thermal radiation emitted by it. Here's a quantitative estimate. Suppose that the hot plate remained intact long enough to do the experiment. For a rough estimate, we can ...
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### Why do metals only glow red, yellow and white and not through the full range of the spectrum?

The physics of why the heated metal glows like a black body has already been thoroughly covered in the previous answers. However, in order to completely bridge the gap with the physiology of color ...
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### Why don't we use infrared light to heat food?

We do use (near) infrared radiation to heat food – whenever we toast food or grill (UK)/broil (US) by beaming infrared downwards on to food! The point is that the infrared is strongly absorbed by the ...
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### Why doesn't the brightness of a bulb change with time?

Two reasons: An incandescent bulb glows not (directly) because it has electricity going through it, but because it is hot. Even when the power going through the bulb decreases, it takes some time for ...
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### Why doesn't hot charcoal glow blue?

Any black body emits radiation of all frequencies. So a hot charcoal definitely emits some blue light. It doesn't appear blue, because most of its light is red, orange, or yellow. To shift the ...
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### Why doesn't the brightness of a bulb change with time?

We already have great answers, but I'll add an anecdote to this: I once played around with several light sources and a scientific camera. The overall experiment was not overly scientific, and I only ...
Accepted

### Cooling a satellite

Typically, satellites use radiative cooling to maintain thermal equilibrium at a desired temperature. How they do this depends greatly on the specifics of the satellite's orbit around Earth. For ...
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### How many X-rays does a light bulb emit?

The formula you want is called Planck's Law. Copying Wikipedia: The spectral radiance of a body, $B_{\nu}$, describes the amount of energy it gives off as radiation of different frequencies. It ...
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### Why does thermal radiation only occur at infrared and visible frequencies?

You are correct. Thermal radiation can have any frequency at all; it depends on the temperature of the radiating body. However, most bodies in the universe have temperatures that make them emit most ...
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### Why is the color of lightning white or blue rather than nothing?

TL;DR: Air in lightning gets hot. Hot things (like the Sun) emit light in a broad spectrum; including visible. You are right there will be emissions outside the visible - but your eye doesn't pick ...
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### If you were invisible, would you also be cold?

Not necessarily. Glass is transparent and it can be heated with convection, conduction and some radiation. It will maintain any temperature around it.
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### Why don't Wien displacement law curves cross?

Here are two reasons they can't cross, one from statistical mechanics and one from pure thermo. Microscopically, each frequency of light is produced by an independent mode. So asking why the curves ...
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