8. The Niagara Falls are 50 meters high. If no heat is lost by evaporation 



how much is the temperature of the water raised by the fall ? (Assume 

 the mechanical equivalent of heat to be 427 gram-meters per calorie.) 



9. How many calories of heat are required to change 5 kilograms of ice at o C. 



into steam at 100 C. ? 



GROUP D 

 Omit one question from this group 



10. (a) Distinguish between the shadow of an object and its image. 



(b) Describe the pin-hole camera. 



(c) A camera which employs a lens is generally made adjustable in length. 

 Is there the same need of adjustment in length in the pin-hole camera ? 

 Give reasons for your answer. 



11. Explain the meaning of the term index of refraction. The index of refrac- 



tion for light passing from air to water being assumed to be 1.3, determine 

 the speed of light in water. (The speed of light in air is 186,000 miles 

 per second.) 



12. The two sides of a paper screen are illuminated equally by a 4 candle-power 



electric light 40 centimeters distant on one side and a gas flame 140 centi- 

 meters distant on the other side. What is the candle-power of the gas 

 flame? 



GROUP E 

 Omit one question from this group 



13. (a) What are the essential parts of the storage cell ? 



(b) What are the chief merits of this cell which are not possessed by the 

 ordinary cell ? 



(c) What are the chief practical uses of this cell ? 



14. Determine the maximum current that may be obtained in an external cir- 



cuit of 4 ohms resistance by employing three cells, each having an electro- 

 motive force of i volt and an internal resistance of 2 ohms. 



15. A current of 10 amperes flowing through a coil of 20 ohms resistance gen- 



erates 1,920 calories of heat in 4 seconds. How much heat would be 

 generated by a current of 5 amperes flowing for the same length of time 

 through a coil of 40 ohms resistance ? 



55 



