Page 2 



Group II 



6. a) Explain why pans of water in a greenhouse may prevent the freezing of 



plants. 



b) Discuss the effect of sprinkling the streets on a hot day with water having 

 J2 the same temperature as the air. 



c) Why are very hot days more unpleasant in moist than in dry climates ? 



7. a) Draw a diagram and explain the use of apparatus such as might be used 



in a laboratory for obtaining distilled water. 

 b) In an apparatus for obtaining distilled water 800 grams of water are con- 

 tained in a copper vessel weighing 300 grams. Both are at a tempera- 

 ture of 20° C. How many calories of heat will be used in heating the 

 containing vessel and in distilling the water? (The specific heat of 

 copper = 0.093.) 



8. a) Explain what is meant by the mechanical equivalent of heat. 



b) In an apparatus for determining the mechanical equivalent of heat the 

 work done in producing the heat was equivalent to the work done by a 

 200-gram weight falling a distance of 78,570 centimeters. If this heat 

 raised the temperature of 28 grams of water, and of a brass receptacle 

 weighing 190 grams which held the water, from 17° C. to 25° C, cal- 

 culate the value of the mechanical equivalent of heat. (The specific 

 heat of brass =0.095.) 



^ Group III 



9. a) What characteristic of a note sounded by a violin distinguishes it from 



the same note sounded by a cornet ? 

 b) What is the vibration rate of an organ pipe which sends out sound waves 

 4.4 ft. long when the temperature is 20° C. ? 



Group IV 



10. It is desired to project a real magnified image on a screen. Would it be pos- 



sible to do this by means of: 



a) A plane mirror ? 



b) A concave mirror ? 



c) A convex mirror ? 



Give reasons for your answers. 



11. Given two converging lenses, one of 1-inch focus, the other of 8-inch focus. 



With the aid of diagrams indicating the manner in which the images are 



formed show: 

 ^ a) How the lenses should be used for a microscope. 



V b) How the lenses should be used for a telescope. 



(THIS EXAMINATION IS CONTINUED ON PAGE 3) 



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