9. A glass pitcher weighing 1,500 grams contains 1,800 grams of tea at 40^0. 

 Ice is used to cool the tea to 10°C. If the specific heat of tea is 1 and 

 that of glass is 0.18, find how many grams of ice are needed. 



Group IV 

 (Omit one question from this group.) 



10. Draw a diagram of a compound microscope showing the lenses used, their 



focal points, and the locations of the images formed; also state the 

 character (real or virtual) of each image. 

 The critical angle for water is 48.5 degrees. Show by a diagram what is 

 meant by this statement. 



11. The image of a post 12 feet high and 20 feet from a camera is 5 inches long. 



(a) How far from the lens is the image ? 



(b) What is the focal length of the lens ? 



12. What is the cause of the apparent color of opaque objects ? 

 Explain why a mixture of yellow and blue pigments appears green. 



Why is it difficult to match certain colors by lamp-light so that they will agree 

 by daylight ? 



Group V 



(Omit one question from this group.) 



13. A man holding a compass under the trolley wire of an electric railway running 



north and south observes that the compass needle deflects toward the 

 northwest. What can you infer from this with regard to the current in the 

 trolley wire ? 



A single loop of wire lies in a horizontal plane and through it is dropped a 

 bar magnet whose north pole is pointing downward. What is the direction 

 of the current induced in the wire while the magnet is approaching the 

 loop ? What factors determine the magnitude of this current ? 



Describe an experiment by which an induced current may be produced by 

 moving a wire forming a part of a closed circuit in the earth's magnetic field. 



14. In a copper refinery a current of 1,000 amperes is employed in a plating bath 



to deposit the metal by electrolysis. How much copper is deposited in 

 24 hours ? 

 (The electrochemical equivalent of copper is 0.0(K)329 grams per coulomb.) 



15. An electric bell of resistance 4.2 ohms is connected by a wire of 1.2 ohms 



resistance to three dry cells, each of resistance . 2 ohm and electromotive 

 force 1.4 volts. 

 What current flows through the bell — 



(a) When the cells are connected in series ? 



(b) When the cells are coimected in parallel ? 



Show by a diagram how the cells are connected in each case. 



109 



