17. Why is water essential for our existence?
18. When can we see light?
19. What happens to the light photons when they bounce back fro
Answers
Explanation:
Water is one of the most important substances on earth. All plants and animals must have water to survive. If there was no water there would be no life on earth. ... Apart from drinking it to survive, people have many other uses for water.
Sometimes you can see light from the Sun passing through clouds and the sunbeams appear as straight lines. After light has been reflected off an object, such as a tree or a book, it still travels in straight lines, but in a new direction. If the light enters our eyes, we see the object (ie our eyes can detect light).
A photon comes from the left of the diagram and decays into an electron and an anti-electron. At the same time, another photon comes from the right and turns into an electron and an anti-electron. Each anti-electron collides with an electron, they mutually annihilate and turn back into a new photon