電磁波穿透力問題 plz help 超急 20點!!!

Light penetration or light absorption in a material depends on the frequency of the electromagnetic wave and the natural frequency of the material. In a classical plasma model, the electrons and protons are like charges connected by springs with some natural oscillation frequency. In a quantum electronic band theory, the natural frequency is given by the energy gap between occupied band and empty band of electrons (E = h f). Example of this is given by the absorption spectrum of an hydrogen atom.

Light are more likely to be absorbed by the material if its frequency is closer to the natural frequency, in which case light has a shorter mean free path, the average distance before light is scattered by absorption and re-emission. The penetration distance is determined by the mean free path, which in turns depends on how close the EM wave frequency relative to the natural frequency.

For example, water has a natural frequency (oscillation of the electron in the O-H bond) close to microwave. [This is also why we use microwave to cook food.] Since red light is closer to microwave than blue, it is better absorbed by water. And therefore blue light actually penetrate better than red in water. The sea appears blue because blue light has a better chance of penetrating into water and reflected by submerged impurity particles.

Another example is given by glass. It has a natural frequency close to ultraviolet. This is why visible light can penetrate through glass but not for certain ultraviolet frequencies. And as red light is farther away from ultraviolet than blue, red light penetrates better in a piece of glass than blue, contrary to the case of water.

Penetration of electyromagentic waves (電磁波) depends very much on their absorption by the medium (介質) where the waves pass through, and the interaction mechansim (相互作用) between the wave and the atoms of that medium. Wavelength (波長) is not a major concern.

A simple example is that visible light can penetrates through glass, but cannot penetrate wood.

Another example is that most electromagentic waves in the visible range penetrate through the atmosphere. But short wavelength ultraviolet (UV-C) is blocked by the ozone layer in the atmosphere. Hence, the saying that short wavelength wave penetrates more than long wavelength wave is not true.
You need to take the wave and the medium together into consideration.

Although X-ray is electromagentic waves in nature, it interacts with matter in a much different manner than electromagentic waves of lower frequencies. X-ray loses its energy by causing ionization.

你係度咬文嚼字，波長愈長，穿透力愈強﹖你睇睇你問題

而紅光等波長較長，可穿透到海底

這不是強，而是長，一個波長300m的電磁波不消半個波長就可到海底，x光穿

透力係粒子反應，同波長無關，一塊鉛板已可阻隔x光。