Experimental steps:
1. Fill the bottle with soybeans, pour in water and cover it tightly with a cork.
2. Put the bottle in a big paper bag, fold the mouth of the bag, and then put the paper bag in a safe and warm place to make the bottle stand upright.
After about 4 days, carefully open the paper bag and see what will happen to the cork.
Dry seeds absorb water and expand when they meet water, which can produce considerable force. This force pushes the bottle in all directions and of course the cork until it bounces off. The power of this seed can even break hard rocks. If your aluminum kettle is flat, you can use this method to restore it. In the cold winter, there is often frost on the windows. Frost is composed of water crystals. If there is a small puddle formed by frost melting on the windowsill. When you look at the puddle, you will find that the frost pattern image of the closed glass window on the puddle is actually colored. Ice crystals are still colorless. Why? Do an experiment to explore.
Experimental materials and appliances: polarizer, frost on the window.
Experimental steps: put a polarizer on each side of the frosted glass, and then observe, you will see that the frost on the glass window is colored. Do you know why you can see colors in this way?
It turns out that ice is a birefringent material, just like a polarizer.
As we all know, there are fast axis and slow axis in birefringent materials. If the polarization direction of light is parallel to the slow axis, the refractive index is higher; If the polarization direction of light is parallel to the fast axis, the refractive index is low. When the emitted light touches the polarizer, whether it can pass through the polarized light depends on the relative orientation of the polarization axis of the light and the polarization axis of the filter.
The influence of birefringent materials on the polarization of light depends on three factors: the refractive index along the fast axis, the thickness of the material and the wavelength of light. If the white light passes through the birefringent material and the filters placed on both sides, although the white light directly enters the first polarizing plate, it passes through the second polarizing filter, so only some wavelengths of light can be seen. If two polarizers or birefringent materials are rotated, the color emitted from the second filter will change.
Therefore, when polarizers are placed on both sides of frosted glass, all crystals with proper thickness orientation will cause color changes. But the crystal whose optical axis is parallel to the line of sight will not produce color, because this crystal will not have birefringence.
Why can you see the color of frost through the puddle instead of the polarizer?
This is because the scattered light from the sky may be strongly polarized. If this light illuminates the window, there is no need to use the first polarizing filter. If light passes through the frost and then reflects from the puddle, it can act as a second polarization filter, because reflection will cause polarization.
In this way, when you look at the puddle where the frost melts on the windowsill, you can see that the frost on the glass window above the puddle is painted with color.