GROUP C 

 Omit one question from this group 



7. What is "the dew point" and how may it be determined experimentally? 



What is the meaning of the term "relative humidity" ? 



8. A copper tea-kettle weighing 850 grams contains 2,000 grams of water at 



temperature 20 C. If, of the heat supplied by a gas flame, 16,000 

 calories per minute are utilized in heating the kettle and water, how long 

 a time would be required to raise the temperature of the water to 100 C. ? 

 (The specific heat of copper is 0.094.) 



9. A liter of air at o C. and 76 centimeters pressure weighs i . 293 grams. What 



is the weight of a liter of air at 20 C., the pressure remaining unchanged ? 



GROUP D 

 Omit one question from this group 



10. Describe a method of producing the spectrum of a luminous body and illus- 



trate the method by a diagram. 



What sort of a source of light will produce 



(a) a continuous spectrum ? 



(b) a bright line spectrum ? 



Explain the manner in which Fraunhofer's lines are produced. 



11. An object 20 centimeters high is placed 15 centimeters in front of a concave 



mirror, the focal length of which is 30 centimeters. 



(a) At what distance from the mirror is the image formed ? 



(b) How long is the image ? 



(c) Is the image real, or virtual? 



12. What are conjugate foci ? 



A distinct image of an object placed 12 inches from a convex lens is pro- 

 jected on a screen 4 inches from the lens. At what distance from the lens 

 would the image be formed if the object were placed 6 inches farther away 

 from the lens ? 



GROUP E 



Omit one question from this group 



13. Describe some form of electric telephone transmitter and some form of 



electric telephone receiver and explain the action of each. 



14. An electric flat-iron of 27 . 5 ohms resistance is connected to a no volt circuit. 



(a) What current in amperes flows through the flat-iron ? 



(b) At 10 cents per kilowatt hour how much would it cost per hour 

 to heat the flat-iron ? 



15. Two incandescent lamps connected in parallel take a current of one ampere. 



Their resistances are 180 ohms and 300 ohms respectively. 



(a) What is the joint resistances of the two lamps in parallel ? 



(b) What current in amperes flows through each lamp ? 



57 



