光是波或是粒子

現代的物理學在量子物理學的角度下，波動和粒子是一而二，二而一的事情，debroglie relation 指出 波長 = 普朗克常數 / 動量，波長明顯地是波動的特性而動量則是粒子的性質，這關係式正是波動和粒子的聯係，事實是很多很多的實驗結果都可以同時由波動和粒子的理論去解釋的，但所涉及的數學處理過程可能十分繁複。想想，如果以粒子去理解問題，只須用加、減、乘和除，你就不會去以波動的方式解偏微分方程去處理問題啦！

閣下的問題可以這樣去看，光有粒子的表現，稱為光子，沒有靜止質量，可產生光壓，有動量，既然有動量，當然有質量。

用波動去處理，一堆不同頻率的波的組合，拉普氏變換所做出的結果也是相當於有 mass 的。

你真的可以用 粒子 或 波動 去理解同一個現象的。

This is quite interesting. I have been asking myself the same question and being confused for a long time too.

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Light do show some wave nature, since you can do experiment of diffraction with light.

However, in PHOTOELECTRIC EFFECT, in this experiment, zinc is exposed to UV light, and electrons are emitted from the metal.
The results are shown as below:
1. Number of electrons emitted depends on the intensity of the light.
2. Energy (Kinetic energy) of the electrons emitted depends on the frequency of the light.
Energy is proportional to frequency
Therefore, there's another formulae about E=hf
E - energy
h - Planck's constant
f - frequency
3. Light need to be in a frequency which is higher than the threshold frequency in order to emit electrons in the metal. Light is packed in quanta.

From the formulae E=hf
It does show particle nature of electomagnetic waves.
This is called wave-particle duality

de Broglie wavelength

wavelength = h / (mv)
[wavelength = Planck's constant / momentum]

Wavelength which is something only waves have, but momentum which is about particles... now both of them are in the same formulae. (HAHA...)

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By the ways, in ELECTRON DIFFRACTION, it does show wave nature of electrons, electrons can be diffracted in a similar way as light and x-ray. (Yes, electrons are particles.)
So that are electrons actually waves?

In modern physics, there is something called photon which is quanta of light. I think that light is just something has both properties of wave and particle. Not everything has the exact answer to it.
So what do you think?

P.S. There is more information about photon in the website below.