8. A wheel is 3 meters in circumference. An iron tire measures 2.993 meters 

 around its inner face. How much must the temperature of the tire be 

 raised in order that it may just slip on the wheel ? (The coefficient of linear 

 expansion of iron is 0.000012.) 



A kilogram of copper, at temperature 90 C., is placed in a cavity in a block of 

 ice whose temperature is o C., and is left there until the temperature of the 

 copper has fallen to that of the ice. It is then found that 107 grams of ice 

 have been melted by the heat given out by the cooling of the copper. Cal- 

 culate the value of the heat of fusion of ice, assuming that the specific heat 

 of copper is 0.095. 



GROUP D 

 Omit one question from this group 



10. What is the cause of the apparent color of opaque objects ? Of transparent 



objects? Explain why a mixture of yellow and blue pigments appears 

 green. 



11. The radius of curvature of a spherical concave mirror is 18 inches. At what 



distance in front of the mirror should an electric arc be placed in order that 

 the reflected rays may be parallel, or nearly so ? 



12. When a screen was placed 3 meters from an object and a lens interposed, an 



image five times as long as the object was projected upon the screen. 



(a) What kind of a lens was used ? 



(b) Where was the lens placed ? 



(c) What was the focal length of the lens ? 



GROUP E 

 Omit one question from this group 



13. Describe the construction of a commercial transformer as used on electric 



lighting circuits and explain its operation. What must be known in order 

 to determine the electromotive force delivered by a transformer when the 

 electromotive force supplied to it is known ? 



14. Describe, in general terms, the apparatus required for electroplating, stating 



particularly the direction in which the current must flow. What strength 

 of current is necessary to deposit 9 grams of silver on a certain object 

 in 30 minutes? (The electrochemical equivalent of silver is 0.001118.) 



15. An electric bell having a resistance of 4 ohms is connected, by wires having a 



resistance of 5 ohms, with two cells connected in series, each cell having 

 an electromotive force of i . 5 volts. The current in the circuit is found to 

 be o . 3 amperes. What is the resistance of each cell ? 



59 



