APPENDIX D. 



PROBLEMS. 

 CHAPTER I. ELEMENTARY ELECTRICITY AND MAGNETISM. 



1. Define the following terms and state the unit in terms of 

 which each is expressed in the c.g.s. system : (a) force, (b) work, 

 (c) potential energy, (d) kinetic energy, and (e) power. 



2. Define the watt. Define the horse-power. Find the num- 

 ber of watts in one horse-power using the following data : one 

 foot = 30.48 centimeters, one pound = 453-6 grams, acceleration 

 of gravity = 980 centimeters per second per second. 



3. (a) Find the number of kilogram-meters per second in one 

 horse-power, (b) Find the number of ergs per second and the 

 number of watts in one kilogram-meter per second. 



4. A pulley 10 inches in diameter runs at a speed of 1,000 

 revolutions per minute and delivers 10 horse-power. Find (a) 

 the torque acting on the pulley in pound-inches, and (b} the tan- 

 gential pull at the rim of the pulley in pounds. Ans. (a) 631.1 

 pound-inches; (b) 126.22 pounds. 



5. (a) Electrical energy for lighting costs 15 cents per kilo- 

 watt-hour, what is the cost per month (30 days) of operating a 

 1 6 candle-power lamp which takes 3.1 watts per candle, the lamp 

 being in service three hours each day ? (b) Electrical energy is 

 supplied at 5 cents per kilowatt-hour for driving a 10 horse-power 

 motor. The efficiency of the motor at full load is 85 per cent. 

 Find the cost per horse-power-hour of the mechanical output of 

 the motor. Ans. (a) 67 cents ; (b) 4.38 cents. 



6. Two steel bars each 50 cm. long, 2 cm. wide and 2 cm. 

 thick are magnetized to an intensity of 800 units pole per square 

 centimeter of sectional area, (a) Calculate the strength of each 

 pole, (b) Calculate the force in dynes, and in pounds, with which 



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