Group IV 



10. a) (2) State the modern theory of light. 



b) (2) How is the spectroscope used to help us in determining what chemical 



elements are present in a body ? 



c) (2) What is the physical difference between blue light and red light ? 



d) (4) A candle and an electric light 64 times as bright as the candle are 9 ft. 



apart in a (Bunscn) photometer. Where between them is the pho- 

 tometer screen when its opposite sides are equally illuminated ? 



11. a) (4) A lens is used to produce a picture 8 ft. high of a three-inch object. 



What focal length does the lens have if the screen on which the pic- 

 ture is formed is 24 ft. from the lens ? 



b) (1) What kind of an image is formed in this case ? 



c) (1) Is the image erect or inverted ? 



d) (4) Make good-sized sketches of the essential optical parts of the eye and 



of the photographic camera. Show their optical similarity by indi- 

 cating the corresponding parts and stating the function of each part. 



12. a) (2) Define the term complementary colors. 



b) (3) Describe an experiment which may be performed to demonstrate such 



colors. 



c) (3) When pulverized blue and yellow crayons are mixed the resulting color 



is green. Explain. 



d) (2) Give the names of two men who have contributed to our knowledge of 



light. What were their contributions ? 



Group V 



13. (10) State the function of each of the following electrical devices: fuse, 



storage battery, transformer, dynamo, motor, rheostat, Wheatstone 

 bridge, induction coil, electroscope, galvanometer. 



14. A 2-ohm coil and a 3-ohm coil joined in parallel are connected in series with a 



5.5-ohm coil and a battery having an electromotive force of 15 volts and 

 an internal resistance of 0.8 ohm. 



a) (3) What is the current in amperes flowing through the 5.5-ohm coil? 



b) (3) What fraction of this current flows through the 2-ohm coil ? 



r) (2) At what rate in watts does the battery generate electrical energy ? 

 d) (2) How much power is being absorbed by the 3-ohm coil ? 



15. a) (3) How long would it take a current of 3 amperes to deposit 16.5 g. 



of copper by electrolysis ? (Electrochemical equivalent of copper = 

 0.00033 g. per coulomb [ampere-sec.].) 



b) (4) To what phenomena do the terms "electrostatic induction" and 



"electromagnetic induction" refer? Describe an example of each. 



c) (3) A compass needle is placed above a wire running north and south. 



What may be inferred if the needle points north ? northwest ? 

 northeast? if it vibrates? 



'^35 



