So fast _____it is difficult for us to imagine its speed.?

A. does light travel that                 B. light travels that

C. as light travels that                  D. with light travels

130. So fast ______ that we can hardly imagine its speed.

The teacher said that ____________________.

       A. light travel much faster than sound        

B. light travelled much faster than sound

       C. light had travelled much faster than sound  

D. light travels much faster than sound

It is not always easy to understand inventions and new developments in science. To understand fiber optics(光纤), however, you can try an experiment.

Put a drop or two of milk into the glass of water. Turn off the lights. Shine the light from your flashlight(手电筒) through the top of the glass at an angle(角度) of about 45 degrees. Put a piece of white paper against the glass when the beam(光束)of light is shining. Move the paper so you can see where the beam is coming out of the glass. You should see a spot of light. Some of the light has passed through the water and through the glass. You see it on the paper. You also see another beam going down into the glass. It is being reflected down into the glass.

Next move the flashlight so that the beam is coming straighter down(30 degrees) into the water. You will see the same phenomenon: some of the light is reflected back into the glass. And some escapes out. Now move the beam of light from the flashlight slowly up until you cannot see any light escaping. This point is called the “point of total internal reflection.” The word internal means “inside.” All the light is staying inside the glass. There is no beam showing a bright spot on the white paper. All the light energy is inside the glass.

The glass of milky water is like a strand(线)of glass. A fiber optic tube is a bundle of long thin strands of glass, really many tubes. However, the principle(原理) is the same: at a certain angle, all the light energy that goes into the glass fiber comes out the other end.

Light is energy. Sound is energy. Radio waves and electricity are both energy. They can all be changed into light, and as light they can all travel along a glass fiber. Light travels at the rate of 186,000 miles per second. Therefore, a message can travel that fast in a glass fiber. This is the principle, or law of nature, that makes fiber optics work.

59.Which figure shows the last step of the experiment?

60. The purpose of the experiment is to tell us          .

A. how fast light travels                             B. how fiber optics works

C. how light travels in a glass of water        D. how fiber optics helps mankind

61.In the experiment,          makes the biggest difference.

A. the angel at which to shine the light from the flashlight

B. the amount of water in the glass of milk

C. the number of drops of milk to pour into the glass of water

D. the size of the hole through which to shine light from the flashlight

62. The last step is to prove          .

A. no beam is shown on the white paper

B. no light can be noticed inside the glass

C. no reflection can be seen

D. no energy is wasted

63. Which of the following can be the best title?

A. Experiment of Light Travel                     B. Principles of Fiber Optics

C. Communication on Fiber Optics              D. Theory of Light Travel