IMPORTANT THINGS ABOUT LIGHT 



103 



1. List four methods of artificial lighting in the order of 

 their historical appearance. 



2. Name all the sources of light that you can think of. 



3. Write a paragraph on how a candle gives light. 



4. Write a paragraph on how a kerosene lamp burns. 



5. The incandescent lamp was invented by . 



6. The filament of the first incandescent lamp was made 



of The filaments of modern incandescent lamps are 



made of . 



7. There are two types of gas lamps in common use today: 

 those with _ _ and those with . 



8. In the carbon arc lamp conducts the current across 



the gap between the two carbons. 



9. Two common liquid fuels used as a source of light 

 energy are 



10. Light is a form of energy. Can you suggest where 

 kerosene and gasoline might have secured their energy? 



11. Scientists have long been seeking a source of cold 

 light. What do you think the greatest advantages of such 

 a light source would be if it could be supplied generally 

 for artificial illumination? 



TOPIC 2. SOME IMPORTANT THINGS ABOUT LIGHT 



SUGGESTED PROBLEMS AND QUESTIONS 



1. What do scientists think light is? 



2. What is the speed of light ? 



3. What causes shadows? 



4. What happens when light strikes an object? 



5. What is the law of reflection? 



6. Under what conditions are rays of light re- 

 fracted? 



7. What is the composition of sunlight? Under 

 what conditions will an object appear black? 

 White? Red? 



8. What are some other ether waves? 



SUGGESTIONS AND HELPS FOR STUDY 



1. Read the problems carefully and be certain that 

 you understand them before you begin your reading. 



2. Do as many experiments as you can as you work 

 out each problem. 



3. Devise an experiment to answer problem 6. Con- 

 sult other general science textbooks for suggestions. 



4. In connection with problem 7 obtain from your 

 teacher a glass prism with which to experiment. 



5. In the study of this topic the following new 

 words may be met for the first time. Study them care- 

 fully and use them as frequently as possible. 



opaque substance substance which does not permit light 



to pass through it. 

 transmit permit to pass through. 

 reflect turn back. 

 refract bend. 

 translucent substance substance which will transmit 



light but which cannot be seen through. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 



Experiment 71. How does light travel? 



Set up apparatus as shown in Figure 152. 



When the holes in the cardboard are not in a straight 

 line, can you see the light? 



From these data what inference can you draw as to how 

 light travels? 1 



Experiment 72. What does a pinhole camera show 

 about how light travels? 



Obtain a small cardboard carton. An empty cereal box 

 will do. Construct a pinhole camera by punching a tiny 



FIG. 152 



FIG. 153 



hole in the center of the bottom of the box. Cover the other 

 end of the box with a piece of translucent paper. Wax paper 

 may be used. Arrange the materials as shown in Figure 153. 

 Look at the image of the candle on the translucent paper. 

 In what position is the image? Do these data support the 

 data of Experiment 71 ? What conclusions are you now 

 ready to draw as to how light travels? 



Experiment 73. Will light rays bend? 



a. Place a coin on the bottom 

 of a fairly deep empty pan. Place 

 yourself so that you can just see 

 the edge of the coin. Have some- 

 one pour water into the pan. Does 

 the coin seem to change position? 

 How do you account for this? 



b. Hold a stick or pencil at an FIC. 154 



angle in a glass of water. Does it appear to be broken at 

 the surface of the water? Does the part of the stick under 

 the water appear to be bent upward? Explain. 



Experiment 74. What causes color? 



Hold a glass prism to your eyes and look at some 

 object through it. Notice the colors which resemble a rain- 

 bow. These are called spectrum colors. 



1 See workbook, p. 38. 



