8. A mass of loo kgm. falls lo meters. All of its energy is employed in stirring 



i,ooo gm. of water contained in a calorimeter which weighs 150 gm. 

 (Specific heat, o. i.) The temperature is observed to rise 2?3 C. Calcu- 

 late the mechanical equivalent of heat. 



9. Define coefficient of expansion. Describe a laboratory experiment by which 



the coefficient of expansion of some substance is determined. 



10. What two classes of images are formed by a concave mirror ? Show by 



diagrams the position of an image of each kind, and explain the principles 

 underlying the construction of the diagrams. 



11. How does the intensity of illumination at a point 2 ft. distant from a 32 



candle-power lamp compare with the intensity of illumination at a point 

 3 ft. distant from the same lamp ? How far away from the above lamp 

 should one's book be placed to secure an illumination upon its pages of 

 2 foot-candles ? (One foot-candle is the illumination produced by a 

 standard candle at a distance of one foot.) 



12. Glass-bottomed boats are frequently used in the observation of the life in 



the ocean. Draw approximately the path of a ray of light, coming from a 

 point some distance below the boat bottom and in the water, as it passes 

 up through the thick glass bottom (index of refraction of glass, 1.5; of 

 water, 1.33) (i) when the direction of the ray is perpendicular to the 

 glass; (2) when the direction of the ray is oblique to the glass. Give 

 reasons for your answers. 



13. Describe briefly some form of galvanometer or ammeter, with diagrams if 



necessary, and explain its action as a measuring instrument. 

 A galvanometer or ammeter having a resistance of 10 ohms is to be 

 connected so as to take only one-tenth of the total current in the main 

 circuit. Explain how this may be done. 



14. If an electric flat-iron takes 5.3 amperes at no volts, what is the resistance 



of the heating element ? How many watts of electric power are required 

 to operate the apparatus ? How many calories of heat should it develop 

 in 10 minutes ? How much does it cost per hour to run the flat-iron at 10 

 cents per kilowatt-hour? (i watt-second = o . 24 calories.) 



15. Discuss the principle and the details of construction of a commercial trans- 



former. 

 Why is it impracticable to transmit electrical power over great distances, such 



as from Niagara to New York City ? What changes in the older methods 



of installation have led to considerable extensions in the practical working 



distances during the last decade ? 

 A commercial transformer was placed on the outside of a building to change 



220 volts to no volts for laboratory use. By mistake the line wires were 



connected to the secondary terminals. What voltage was obtained in the 



laboratory ? 



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