Photons - Sixty Symbols

Why is a photon like a cricket ball? Find out in this video about "light particles". More at http://www.sixtysymbols.com/

Category:

Science & Technology

Tags:

• photon
• light
• sixty
• symbols

[astropixie101]

photons have relativistic momentum.

using einstein's famous energy equation and adding the relativistic momentum term (giving the general energy expression):

E^2 = (m^2) x (c^4) + (p^2) x (c^2)

E is energy, m is rest mass, p is momentum, c is speed of light. photons have zero mass so E = pc. the E of photons exist in distinct packets that only depend on the frequency, f (or wavelength) (the photoelectric effect)... E=hv, h is plancks constant.

so E = pc = hf and finally, p = hf / c

[materiasacra]

Usually I have great admiration for the sixtysymbols videos. But the explanation of Rayleigh scattering at 5:30 makes no sense.

The wavelengths from red down to blue are all much larger than the size of a molecule. In all cases the molecules 'experiences' an effectively uniform electromagnetic field, oscillating very rapidly. It is easy to show that this gives rise to the famous 1/lambda^4 spectrum of Rayleigh scattering.

[wreynolds1995]

@RasmusLastname Hmm. I think I know where this confusion is, and I'll admit I'm partly at fault.

Out of interest, where (or, if it's in the video, when) did you get this idea of a "quantum of energy"? Was it an exact quote or did you paraphrase someone?

[RasmusLastname]

@wreynolds1995 "In physics, a quantum (plural: quanta) is the minimum amount of any physical entity involved in an interaction" (Wikipedia) So, since they're all photons, shouldn't the quantum of light always be a specific energy level? I'm not saying you're wrong, I know you're right, I'm just trying to understand it better. It would be really helpful if you could answer ^^

[wreynolds1995]

@RasmusLastname No. When we say "a quantum of energy," it's the same as when we say "a packet of light", see? It just means a little bundle of the stuff.

In fact, the greater the energy of the light, the greater the frequency of the light. Need proof? Handheld lasers. Red light has a greater wavelength (and so less energy) than green light, and same for green light and blue light; hence why red lasers aren't as dangerous as green lasers, and why green lasers cost more.

[wabs05]

lol "for all us english speakers" good one sixty symbols!

[RasmusLastname]

If a photon is a quantum of energy how can they have different energy values? Isn't quantum sort of a minimum value?

[RustlessPotato]

@UmlautBanana actually you do i think. it's just infintesimally small you don't really feel anything.

[Tatlreach]

this one was really boring for me until learning about the why the sky is blue

[UmlautBanana]

Wait... if photons are particles, why don't you get a recoil force from, say, switching on a flashlight?

[stagedive516]

@QQonmyPP

No, she's from the US so she accidentally called it a flashlight, and he corrected her for the UK viewers who call it a torch.