Shulou(Shulou.com)11/24 Report--

This time it is not the shadow that disappears, but a real object that disappears!

Is it quantum mechanics?

Don't worry, next I'll show you what's going on.

The experimental equipment is a water basin, a transparent cup and a coin (well, a coin-like dog head is also fine)

The first step of the experiment: fill the cup with water, then quickly pour it over the coins in the basin, make sure that the water in the cup is higher than the surface of the basin, and keep an oblique view of the coins while moving the cup.

Step 2: first keep the coin in the inverted cup, gently press and hold the cup, and then add water to the basin, making sure that the water in the cup is lower than the surface of the basin. Also move the cup while maintaining an oblique view of the coins inside the cup.

Did the coins just disappear in your eyes?

Step 3: do a comparative experiment so that there is no water in the basin and the cup.

Ha, no matter how you move it, you still have the coins!

Principle explains that when light is incident from one medium to another, the direction of propagation will change, that is, the refraction of light. The refraction of light satisfies the law of refraction.

Where n "and n" are the refractive index of incident medium and outgoing medium respectively, and θ "and θ" are incident angle and exit angle respectively.

When the incident angle θ is 0, sin θ is 0, and the θ is 0, that is to say, when the light is incident perpendicular to the interface, there is no refraction.

It can be seen from the refraction law that the refraction angle increases with the increase of the incident angle. When the incident angle reaches the critical value, θ'= arcsin'(n'/ n'), the θ 'reaches the maximum value of 90 °. When the incident angle continues to increase, the refracted light will disappear and all the light will be reflected at the interface, that is, total reflection.

There are two conditions for the total reflection phenomenon: the incident angle is greater than the critical value, and the light incident from the medium with high refractive index to the medium with low refractive index.

In our nut disappearance experiment, the light of the nut shoots from the water into the air and then into the human eye, and the refractive index of water is higher than that of air. After we join the cup, the refractive surface changes, and the angle of incidence can be greater than the critical angle. Total reflection will occur, no refraction of light into the air, the nut will be "invisible" in our eyes.

When there is no water in the cup, it is similar to the situation with water, except that the interface of total reflection has changed. The light is incident into the water by θ, the refraction angle is θ, and then refracts into the air from the water, and at this time the incident angle is the residual angle of θ, which is larger than the critical angle, so the total reflection occurs and the nut is "invisible".

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: Ah Yi & Xiao Pa & iu

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