294 



ADVANCED ELECTRICITY AND MAGNETISM. 



sents the orbit of a cannon ball, D being the horizontal distance 

 traveled by the ball in a given time and d being the vertical 

 distance fallen by the ball under the action of gravity. If D 



Fig. 215. 



is known and d observed, then the velocity of the cannon ball 

 is given by the equation: 



+--& (o 



in which g is the acceleration of gravity. 



Action of the electrical field on a moving charged particle. 

 Consider a charged particle moving upwards through an elec- 

 trical field as shown in Fig. 216. Let q be the charge on the 



H 



-f 

 + 

 +1 



^ 



-M 



lead block \ | lead block 



Fig. 216. 

 Electric field from right to left. 



lead block 



lead block 



Fig. 217. 



particle in abcoulombs and e the intensity of the electrical field 

 in abvolts per centimeter. Then the force F in dynes pulling 

 sidewise on the particle is equal to qe, so that the acceleration of 

 the particle in the direction of F is qe/m, where m is the mass 

 of the particle in grams. It is evident that the particle moves 



