134 ADVANCED ELECTRICITY AND MAGNETISM. 



-tfpll+a 



ilh 



c 



Fig. p3. 



Fig. #4. 



Note. An electromotive force E + e will cause a certain amount of charge Q 

 to circulate around the circuit in Fig. p4; and Q = C'(E + c) where C' is the 

 combined capacity of the two condensers in series. But Q = CE and Q = ce, 

 and, if we substitute the values of E and e from these equations in Q = C'(E -f e), 

 we get an equation from which Q cancels out and which can be solved to give C' 

 in terms of C and c. 



5. An electromotive force acting on a condenser increases at 

 a uniform rate from zero to 100 volts during an interval of 0.005 

 of a second. The capacity of the condenser is 20 microfarads. 

 Find the value of the current during 0.005 f a second. Ans. 

 0.4 ampere. 



6. An alternating electromotive force which is represented by 

 the ordinates of the zigzag line in Fig. p6 acts on a circuit which 



1 1 00 VOltS 



Axis of 



fioo second 



Fig. p6. 



contains a condenser. The resistance of the circuit is negligible, 

 and the capacity of the condenser is 20 microfarads. Plot the 

 curve of which the ordinates represent the successive instanta- 

 neous values of the current. 



