Can you explain simply what is a 'black body'?

Question

and what's it got to do with the photoelectric effect?

I choose best answer if one is worthy

thskjs

Answer 1

Black bodies are objects that absorb and and emit all electromagnetic radiation. The black body heats up when exposed to electromagnetic radiation and as it heats up it emits radiation.

As the black body becomes hotter, the wavelength of light that it gives off the most of become higher in frequency and increases in intensity. You can see this as a black body radiation curve.

This is why cooler stars and maybe heaters and stoves you see as red, as you heat something more the colour becomes whiter and whiter and eventually blue and then beyond what we can see, into ultra violet and so on.

The thing with black body radiation was, it couldn't be explained by classical physics. To fix this up, this german dude named max planck hypothesised that light comes in packets which have discrete amounts of energy (multiples of a number we know as Planck's constant). With this hypothesis of his, he was able to predict black body curves that have a higher frequency and get correct results!

By suggesting that light comes in packets, he sort of said photons exist, these photons are particles of light. The more photons there are, the higher the light intensity is and the higher the frequency of light is, the more energy these photons have.

Now to relate this to the photoelectric effect. The photoelectric effect is the phenomena where light (and other electromagnetic radiation) can knock electrons off a metal surface.

The problem with this photoelectric effect was that classical physics couldn't explain it either! there was a minimum frequency of light required to knock electrons off an atom and no matter what the intensity of light was shone on it, if the frequency wasn't high enough the electrons wouldn't get knocked off.

To explain this, einstein used Planck's hypothesis which took light as packets.

Einstein said that a minimum energy was required by a photon to knock electrons off. He also said the intensity of light can only affect the number of electrons that are emitted as there are more photons to cause the photoelectric emission.

I hope i have explained this properly, if you have any questions just message me.

Maybe visit these websites for more info:

http://hyperphysics.phy-astr.gsu.edu/hba...

http://hyperphysics.phy-astr.gsu.edu/hba...

Also, I highly recommend reading the first few sections on the link that maussy sent, its very intresting!

Answer 2

Actually a Black Body is the one which absorbs every radiation and is also able to emit every radiation.

The perfect example of Black Body is the UNIVERSE itself. If you light a torch (or any thing that emits radiation) in the night sky, the light will never come back.

On the other hand, you receive radiation of every frequency from universe including visible light if you are given with right kind of receiver.

Answer 3

Something that absorbs light... like a lake.

Answer 4

A black body absorbs all visible radiation. The best black body will be soot. hen heated a black body emits radaition in the same manner that it absorbs. the emission is triggered by Wien law. Interest of this law is that you can measyre the temperature analyzing the light emitted

Look, at the link