GROUP D. (Omit one question from this group.) 



10. How is the bending of a ray of light passing from air into water explained 



by the wave theory of light ? Illustrate by means of a diagram. 



11. Describe a method by which the velocity of light has been determined. The 



distance from the earth to the sun is approximately 93,000,000 miles. 

 How long a time is required for light to traverse this distance ? 



12. At what distance from a 4o-candle-power mantle burner would a newspaper 



receive the same illuifiination as it would receive from an 8-candle-power 

 incandescent lamp 2 feet distant from it ? 



GROUP E. (Omit one question from this group.) 



13. How does a charge of electricity distribute itself on an insulated conducting 



body such as a metal pail or cup ? How is the distribution tested experi- 

 mentally ? 



14. An electric motor, found, by a brake test, to develop 2 horse-power, requires 



8.25 amperes at an electromotive force of 220 volts. What is the efficiency 

 of the motor, expressed in per cent ? 



15. A galvanometer has a resistance of 171 ohms. With what resistance should 



it be shunted in order that only one-tenth of the current in the main circuit 

 may pass through it ? 



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