An elementary book on electricity and magnetism and their applications . a fall 25 feet high; the power of the water is4000 X25 or 100,000 foot pounds per minute or a little over three horsepower. It should be noted, however, that this is the power of thetailing water, and only 80 to 90 per cent of it could be converted intomechanical power by an ordinary water wheel. In a similar way the horse power of a steam engine is an engine is supplied with steam at an average pressure of40 pounds per square inch, and that the piston is 100 square inches;then the total force against t
An elementary book on electricity and magnetism and their applications . a fall 25 feet high; the power of the water is4000 X25 or 100,000 foot pounds per minute or a little over three horsepower. It should be noted, however, that this is the power of thetailing water, and only 80 to 90 per cent of it could be converted intomechanical power by an ordinary water wheel. In a similar way the horse power of a steam engine is an engine is supplied with steam at an average pressure of40 pounds per square inch, and that the piston is 100 square inches;then the total force against the piston is 4000 pounds. If the strokeof the engine is 1 foot, the piston moves 2 feet in every revolution,and consequently the steam does 4000X2 or 8000 foot pounds of workeach revolution. If the engine runs at 250 revolutions per minute(), the work done by the steam is 250X8000 or 2,000,000 footpounds per minute; therefore the engine is doing work at the rate ofa little more than 60 horse power. This is called the indicated horsepower of the engine. PLATE James Watt (1736-1819). A Scotch instrument maker at the University of Glasgow, famous for his im-provements on the steam engine, which were so important and fundamentalthat he is often called its inventor. The modern industrial age may be saidto begin with Watt. ELECTRIC POWER AND HEATING EFFECTS 69 Problems 1. A horse draws a plow for 2 hours at an average rate of 2 milesan hour and exerts an average pull of 125 pounds. How much workdoes he do? What is the horse power? 2. What is the horse power of an engine that can raise 3 tons toa height of 22 feet in 2 minutes? 3. How many horse power are there in a waterfall 30 feet high overwhich 500 cubic feet of water pass each minute ? (1 cubic foot of water weighs pounds.) 4. How much work can a 5-horse-power engine do in 15 minutes? 5. To what height could a 10-horse-power fire pump send 50 cubicfeet of water per minute? 6. A fire engine is used to pump out a ce
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