Is there any mention of the convex lens concentrating effect in ancient Chinese literature?

Huainan Wanbi Technique".

Created in the 2nd century BC.

Author: Liu An, King of Huainan.

Category: Important literature on physics and chemistry.

Huainan Wanbi Technique" Records about the fire of the ice lens: "Cutting the ice makes the circle, lifting it to the sun, and taking the shadow of Ai to bear it, then the fire is born." "To make fire, it is customary to use the heating method, but here it is achieved with ice.

This account is not fanciful, and the Qing Dynasty optician Zheng Fuguang has already proved with simulation experiments that it is feasible to use ice lenses to make fire. And this article explicitly mentions the focusing nature of the lens, which is also valuable.

At the end of the Qing Dynasty, Zheng Fuguang once did a simulation experiment, he used a tin pot with a slightly concave bottom, filled with hot water, and ironed on the excavated ice cubes to obtain a crystal clear ice lens, and then used it to make fire to the sun, and achieved success. He summed up the essentials of using an ice lens to make fire: "But it must be full of sunlight, the ice is bright and the shape is large and slightly shallow (about three inches in diameter, and the outer limit must be about two feet), and it must be stable and unshakable, and it must be slightly slow."

Fei Yin is the same as Zhilu Ice Cutting Fire Convex Mirror") Zheng Fuguang's experience makes sense.

Technical principle. The light-gathering ability of the lens is the square of the ratio of its aperture to the focal length (relative aperture), so that the lens with a large aperture is conducive to the improvement of the light-gathering ability. On the other hand, the shallow degree of convex is the large focal length, and the large focal length is not conducive to light collection, in this regard, Zheng Fuguang went on to explain:

The cover fire is born in the heat of the sun, although it is not vitrinoid, but the ice has a cold air, which can reduce the heat of the day, so it must be convex and shallow in diameter, so that the cold is far away and sufficient. "Originally, this is due to the fact that the ice is cold, and the cold is going down, so the focal length should be slightly larger to reduce the effect of the cold of the ice lens, so that the fire is easy to succeed.

ps: In ancient China, crystals were used to polish lenses, and many of these lenses were unearthed; It is even said to be 3,000 years old.

If you go to Mengxi Pen Tan, it records in detail the research on optics in ancient China, and there are principles such as convex lenses and light gathering.

If you go to Mengxi Pen Tan, it records in detail the research on optics in ancient China, and there are principles such as convex lenses and light gathering.

Remember: the near and far images of things become smaller, and the far images of things become larger

Theoretically, both concave and convex lenses are capable of concentrating light.

But in reality, special convex lenses disperse light.

Because it is easy and convenient to do the problem, it is said that both the concave mirror and the convex lens can gather light, just like the resistance of the wire is 0 when doing the problem, but in fact (the laboratory) can measure that the wire has resistance.

Under certain conditions, convex lenses are able to diverge light.

Convex lenses are light concentrating, and concave lenses are astigmatism.

Depending on which point of view, after converging into one point, of course, it is divergent.

In the ancient Greek wars, the concave mirror was used to concentrate light, not a convex lens.

Legend has it that 2,000 years ago, the ancient Greek city of Syracuse was invaded by the Roman army, and men had their own war posts, Archimedes organized women and children to fight on bridges, and told them to bring all the mirrors that could be moved, and stand in a designated place by the sea. When the sun shines strongly on the earth, Archimedes gave an order, and the women and children are all bright, reflecting the sunlight on the Roman sailing ship, and after a while, the sail is on fire, and the Roman soldiers are cried wolf by the burning ghosts, and Archimedes borrowed the heavenly fire to defeat the invading army, and some people say that this is the first time in the history of war to use optics.

Analysis: Archimedes organized the women and children and told them to bring all the mirrors they could move and stand in a designated place by the sea. In effect, these mirrors were formed into a huge concave mirror, which would gather sunlight, and the temperature at its focal point was so high that it set the Roman sailing ship on fire.

Take a piece of paper in one hand and a convex lens in the other, place the convex lens between the paper and the sun, adjust the distance between the paper and the convex lens, and you will see that there are bright spots on it, indicating that the convex lens has the effect of convergence.

First there is light concentrating, and then there is imaging. There are magnified virtual images and magnified (reduced) real images.

The property of convex lenses is that they have a converging effect on light, of course.

This is based on the refraction of light. If you really want to ask why, I can't really say.

The convex lens can be seen to be composed of countless prisms, which deflect the light towards the thickness, so the convex lens has a converging effect on light.

This is the phenomenon of light refraction in physics, and we know that when light rays enter from one medium to another, the light rays will be deflected and no longer propagate in the original direction of propagation, which is the refraction of light. For a general transparent medium such as glass, if it is a cuboid structure, or at least two sides are parallel to each other, then the light enters the glass from one side and then emits out from the other side, then the incident ray and the outgoing ray are parallel.

But for a glass body like a convex lens, because the two faces are not parallel, but a convex, then the light will be deflected in the process of propagating inside, and the deflection direction is to the thicker side, because the common convex lenses are round, and the outer thin and the inner thick, so the final light is segregated to the middle, and finally converges at a point on the perpendicular line of the convex lens, forming the bright spot we see, in physics, we call this point the focus. This is the concentrating principle of convex lenses.