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Group III 

 (Omit one question from this group.) 



7. a) Define dew point. 



h) What is meant by the relative humidity of the air ? 



c) How may the relative humidity of the air be experimentally determined ? 



8. If gas costing $1 .00 per 1,000 cubic feet furnishes GOO B.T.U. of heat per cubic 



foot of gas burned, how much would it cost to raise from 62° F. to 212° F. 

 one quart (2 pounds) of water by means of a burner and kettle having a 

 combined efBciency of 50 per cent ? 



9. a) Describe in detail an experimental method for determining the specific 



heat of a substance. 

 h) Explain how a numerical result may be secured from the data obtained. 



Group IV 

 {Omit one question from this group.) 



10. In a darkened room a spectrum of sunlight is thrown on a screen. A bouquet 



of red, yellow, and blue flowers with green foliage is placed in the red end 

 of the spectrum and gradually moved toward the violet end. State and 

 explain what would be observed. 



11. a) Describe the construction and explain the operation of the so-called 



"pin-hole" camera. 



b) If such a camera is 8 inches long and the image of a building 50 feet high 

 appears as an image 3 inches high on the plate how far away is the 

 building ? 



12. a) Represent by a diagram the path of the rays of light through the lenses 



of an astronomical telescope. 

 b) A telescope has an objective whose focal length is 30 feet and an eye-piece 

 whose focal length is 1 inch. What is the magnifying power of the 

 telescope ? 



Group V 

 (Omit one question from this group.) 



13. a) Given one battery, one bell, two push buttons, and a quantity of wire, 



represent by a simple diagram a scheme for wiring a house so that the 

 bell may be rung from either the front door or the back door. 



b) Why is it advantageous to use a high voltage for the transmission of elec- 



tric energy over long distances ? 



c) Why are alternating currents used for long distance electrical transmission ? 



14. A 17-candle-powcr carbon filament lamp takes 0.6 ampere at 110 volts. 



A 2G0-candle-power gas filled tungsten filament lamp takes 1.85 amperes 

 at 110 volts. Compare the efficiencies of the two lamps. 



15. The poles of a storage cell having an electromotive force of 2 volts and an 



internal resistance of 0.1 ohm are connected by two wires in parallel whose 

 resistances are 12 ohms and 4 ohms respectively. 



a) What current flows in each wire ? 



b) What current flows through the cell ? 



