Group IV 

 (Omit one question from this group.) 



10. Show, by means of a diagram, the least height of a vertical plane mirror which 



would enable a man 6 ft. tall to see a full length image of himself. 

 Why does a shallow pond, when viewed from one side, appear to be less 

 deep than it really is ? 



11. If the illumination necessary for reading is 2 foot-candles, how far away 



from a reader may a 16 candle-power lamp be placed ? (One foot-candle 

 is defined as the intensity of illumination produced by a source of light 

 of one candle-power at a distance of one foot from that source, the light 

 falling perpendicularly.) 



12. An object 6 in. long is placed 20 in. in front of a concave mirror whose radius 



of curvature is 2 ft. 



(a) Where, and at what distance from the mirror, is the image ? 



(b) What is the length of the image ? 



Group V 

 {Omit one question from this group.) 



13. Why are high potential currents employed for the long distance transmission 



of electrical energy ? Explain the use of transformers as employed on 

 transmission circuits. 



14. Given three 1 10- volt incandescent lamps, each requiring . 5 ampere. Find 



the voltage required, the resistance of the circuit and the current in the 

 circuit. 



(a) when the lamps are connected in series; 



(b) when the lamps are connected in parallel. 



15. An electric heater connected to a 110-volt circuit takes 600 watts. How 



many calories of heat does it develop in 10 minutes ? 



107 



