Chapter 14

This chapter is a world of light. Light is essential to life. Plants and animals are governed by the rhythm of day and night. Sunlight provides the energy for the food-making process in green plants. The fossil fuels are the store of the solar power that winged down from the sun millions of years ago. When the fuels are burned, the sun energy locked in their molecules is liberated as heat and light.

Scholars and scientists at all times tried to explain what is light. Some of oldest people believed that light was a kind of emanation from the eye. Newton proposed that light was a stream of particles or corpuscles shot off by a luminous body. A few people were in favor of the theory that light was a vibration. Einstein theorized that a beam of light is a shower of small packets of energy, which he called photons.

The white light is the combination of red, orange, yellow, green, blue, and violet lights. When a beam of white light passes through a triangular glass prism, a rainbow of all these colors will appear on a screen. Certain objects have their own property. They absorb some kinds of colors while reflecting some at the same time. The reason for the red we see in the rose petals is that these petals absorb most of other kinds of colors while reflecting the red light.

That the sky is blue is because the lower parts of atmosphere scatter more of the blue light than the others. That the sun appears yellow is due to the combination of the remaining colors apart from blue in the sunlight.

Light is bent or refracted when it passes obliquely from a medium of one density to another. That is why chopsticks look crooked when part of them is in the water.

Two types of lenses people use everyday are convex lenses and the concave lenses. The convex lenses are used for converging light, whereas the concave lenses are used for diverging light.

Visible lights resemble other forms of radiation, such as radio waves, x rays, and cosmic rays in that they travel at the same speed in the same medium. The only difference is the wave length.