GROUP C. (Omit one question from this group.} 



7. a) Why does sprinkling the floor with water cool the air? 



b) Why is a clear night generally cooler than a cloudy one at the same season ? 



c) Why can you "see your breath" on a cold day ? 



8. When 1,000 grams of ice at o C. are put into 2,500 grams of water at 60 C. 



the temperature of the whole becomes 20 C. Find the heat of fusion 

 of ice. 



9. Neglecting loss of heat by radiation find how much steam at 100 C. is required 



to raise the temperature of an iron radiator weighing 60 kilograms from 

 10 C. to 100 C. (The specific heat of iron is o. n.) 



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



10. Explain by means of two diagrams, one showing the unaided eye and the 



other showing the eye assisted by a suitable lens, the effect produced by 

 eye glasses which would enable a far-sighted person to see distinctly 

 objects near at hand. 



11. An object i foot high is placed 2 feet from a convex lens having a focal length 



of 1 8 inches. 



a) Find the position and size of the resulting image. 



b) Is the image real or virtual ? Erect or inverted ? 



12. How may a distinct sun spectrum showing the Fraunhofer lines be obtained ? 



How are the Fraunhofer lines explained ? 







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



13. Why do the leaves of a gold-leaf electroscope diverge when a positively 



charged body is brought near, although no charge passes from the charged 

 body to the electroscope ? 

 Indicate the distribution of the charge by means of a diagram. 



14. Given a voltaic cell, a coil of wire, an ammeter, and a voltmeter, how may the 



resistance of the wire be determined ? 



Illustrate by means of a diagram the manner in which the apparatus is 

 connected in the circuit employed. 



15. Three voltaic cells, each having an electromotive -force of 1.4 volts and a 



resistance of o . i ohm, are connected with a wire having a resistance of 

 3 . 9 ohms. Find the strength of the electric current 



a) When the cells are connected in series; 



b) When the cells are connected in parallel. 



