Question

which experiment shows that light is a particle ?

Answer 1

I think the double-slit experiment showed light as a particle...

Answer 2

the double slit experiment show light is waves

the photoelectric effect shows light is particles

Answer 3

how photoelectric effect showed the light is a particle ? @Unklerhaukus

Answer 4

You know characteristics of the effect @chmvijay?

Answer 5

To fast go over the characteristics we can try think like Einstein did:
1. No electrons are ejected, regardless of the intensity of the radiation, unless the frequency of the radiation exceeds a threshold value characteristic of the metal.

2. The kinetic energy of the ejected electrons increases linearly with the frequency of the incident radiation but is inde- pendent of the intensity of the radiation.

3. Even at low light intensities, electrons are ejected if the frequency is above the threshold.

Okay the way Einstein explained this way to suggest that the photoelectric effect depends on the ejection of an electron when it is in some kind of collision with a "particle-like" projectile, that carry enough energy to eject the electron from the tested metal.

Okay to put a litte more math to it we get to understand everything:
Assume that the projectile is a photon, a particle of electromagnetic radiation, with the energy \(hv\) (the Planck relation), where \(v\) is the frequency of the radiation. It most then follow from the conservation of energy that the Planck relation is equal to the kinetic energy of the ejected electron.
\[\Large \frac{ 1 }{ 2 }mv ^{2}=hv-\Phi\]
Where \(\Phi\) (uppercase phi) is the "work function for the specific metal" which is the energy required to move the electrons from the metal to infinity. A good illustration could be the following:


The double slit experiment show light behave like waves or subatomic particles, like the electron, show wave-like nature (The reason I say "wave-like nature" is due to the fact we still see the electrons as dots!!) just as UnkleRhaukus say.

Answer 6

is photon a particle ? LOL

Answer 7

Everyime you say "photon" you choose to consider light (electromagnetic radiation) as a particle. We even got a fine little spot for the particle in our standard model.
http://upload.wikimedia.org/wikipedia/commons/0/00/Standard_Model_of_Elementary_Particles.svg

Answer 8

but it is not having mass right :P

Answer 9

Correct.

Answer 10

then how is it particle though it wont have mass then ?

Answer 11

a photon does not have mass , but it will have momentum

Answer 12

then its momentum is due to its velocity ? the MV doesn't hold good any more ?

Answer 13

the momentum of photon of frequency \(\nu=\dfrac c\lambda\)
(angular frequency \(\omega=2\pi \nu\))

\[p=h\nu=\hbar\omega\]

Answer 14

where h is planks constant
and \(\hbar=h/2\pi\)

Answer 15

p= hv ?

Answer 16

p=hν

Answer 17

how can this be ? then energy and monentum are same ?

Answer 18

Use the extended mass–energy equivalence:
\[\Large E ^{2}=\color{red}{(mc ^{2})^{2}}+\color{blue}{(pc) ^{2}}\]
Where the \(\color{red}{red}\) expression is for particles with mass, but no velocity. And the \(\color{blue}{blue}\) expression for particles with no mass, but velocity. Guess you can understand it that way?

Answer 19

I made a mistake. Where I said velocity, write momentum instead.

Answer 20

\(m=m_0=\)rest mass

Answer 21

Oh yea that too.