2/2 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



diameter of the pitch circle of each gear is 2 feet. Find : (a) 

 The tangential force exerted on a given gear wheel by each ad- 

 jacent wheel, and (b) the torque exerted upon a given gear by 

 each adjacent gear and express the result in pound-feet Ans. 

 (a) 2 1 pounds, (fi) 2 1 pound-feet. 



144. A long wire of which the resistance per centimeter of 

 length is 0.02 ohm carries a current of 3 amperes, (a) Find the 

 rate at which energy flows in upon each centimeter of length of 

 this wire in ergs per second. () Find the intensity of the 

 energy stream at a distance of 1 5 centimeters from the wire in 

 ergs per second per square centimeter, (c) Find the intensity of 

 the electric field parallel to the wire in abvolts per centimeter and 

 find the intensity of the magnetic field in gausses at a distance of 

 15 centimeters from the wire. (</) Find the value of the pro- 

 portionality factor by which the product of intensities of electric 

 and magnetic fields (at right angles to each other) must be mul- 

 tiplied to give the intensity of an energy stream in ergs per 

 second per square centimeter. Ans. (a) 1,800,000 ergs per 

 second. (3) 19, 100 ergs per second per square centimeter, (r) 

 6,000,000 abvolts per centimeter, (d} 1/473". 



145. Consider two line wires in the form of two flat metal rib- 

 bons 50 centimeters wide and 3 centimeters apart. At a given 

 point // the electromotive force between the ribbons is 100 volts 



o'.ioo volte !3<si. 



p 



amperes ~~ = _ 



Generator r*- 



ead 10 Amperes 



Fig. 203. 



and the current in each ribbon is 10 amperes, as shown in Fig. 

 203. (a) Find the rate in ergs per second at which energy flows 

 past the given point p from generator towards receiver in 



