# Why we use wavelength to divided into ray, wave and particle

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1. Sep 11, 2015

### isnainidiah

I want to ask something about light, light can be defined as ray, wave, or particle. The group formed because of the wavelength, if the wavelength is less than the dimension of equipment it is grouped into ray, if the wavelength is equal to the dimension of equipment it is grouped into wave, and the last if the wavelength is bigger than the dimension of the equipment it is grouped into particles/foton. My question is, why we use wavelength to divided into ray, wave and particles ?

2. Sep 11, 2015

### blue_leaf77

When the wavelength is much smaller than the typical equipment size, phenomena inherent to a wave, such as interference and diffraction, are much less apparent - such light passing through an iris will practically be just going through it with the beam size after is the same as the iris opening.
Interference and diffraction become important.
Have never heard of it, but I suppose, when the measuring element is much smaller than the wavelength, the sensitivity to the electric field fluctuation may be excalated. This is the realm of quantum optics.

3. Sep 11, 2015

### isnainidiah

But, why wavelength is choosen as parameter ?

4. Sep 11, 2015

### blue_leaf77

I believe the answer to this question is already implied in my previous post.

5. Sep 11, 2015

### isnainidiah

I mean, why not another quantity such as amplitudo or frequency become the parameter ?

6. Sep 11, 2015

### blue_leaf77

Frequency can also be used in place of the wavelength as these quantities are related by $c=\lambda f$. It just happens that we use wavelength more often than we do frequency. You are right, in some cases, actually the intensity of the light, which is directly related to the amplitude must also be taken into account as to whether we should resort to treating the light as classical wave or quanta. In particular, when the intensity is very high (meaning this light beam contains thousands of million of photons) it's sufficient to treat it as a classical wave. If there is only a few photons (let's say below a hundred), then we must resort to the quantum treatment which is quantum optics.
PS: I recognize your name is native to certain southeast Asian countries.

7. Sep 11, 2015

### isnainidiah

Hmmm i got the idea,, thank you for your explanation
Yeah, you're right i come from southeast asian countries