52 ELECTRICAL ENGINEERING PROBLEMS 



12. Two condensers of 10 and 15 microfarads are in parallel; 

 what is the combined capacity? What would it be if they were 

 in series? (1 ram.) 



13. Two condensers have capacities of 1 and 20 microfarads; 

 what are the combined capacities when they are in parallel, and 

 when they are in series? (1 mm.) 



14. With the condensers of problem 13 in series on a 1000-volt 

 circuit, what would be the voltage around each condenser? How 

 could this arrangement be used in voltage measurement? (3 ram.) 



15. A 50-microfarad condenser charged to 2000 volts is con- 

 nected to a non-inductive circuit of 100 ohms. Obtain, by approxi- 

 mate method, and plot a curve between terminal e.m.f. and time. 

 Get points for 1, 2, 3, 4, 6 and 10 thousandths of a second; make 

 approximations enough to locate the curves within 2%. (10 ram.) 



16. From the curves obtained in problem 15 determine the 

 instantaneous value of the current at 0.0024 second after the 

 beginning of the discharge. (1 ram.) 



17. The condenser of problem 15 is connected through the 100- 

 ohm circuit to a 2000-volt e.m.f. Obtain the charge at the end of 

 1, 2, 3, 4, 6 and 10 thousandths of a second and plot the same. 

 (12 ram.) 



KA 



18. Using the formula: Capacity = ^ , ft5 microfarad, 



oo Trd X 1" 



where A and d are area and distance, between plates in centimeters 

 and K is the inductivity of the dielectric, determine how many 

 square meters of glass plates 3 mm. thick with copper foil on 

 each side would have to be used to provide a 0.045-microfarad 

 condenser for -a 5-kw., 25,000-volt wireless sending outfit. Take 

 the inductivity of the glass used as 6. Neglect the capacity 

 between the adjacent plates. (8 ram.) 



19. As an alternative form of condenser for the above case, 

 determine the number of metal plates 40 centimeters square, that 

 would have to be immersed in petroleum with an inductivity of 2.2 

 and spaced 1 centimeter apart to give the same capacity. (4 ram.) 



