424 PROBLEMS AND EXERCISES. 



Ans. Through X i -05 webers per sec. 



Through Y 0-1909 ,, 



Through Z 0-0207 ,, ,, 



Through all three 1-105 , , , , 



11. Calculate the number of cells required to produce a 

 current of 50 milliwebers, through a line 114 miles long, whose 

 resistance is 12 \ ohms per mile, the available cells of the battery 

 having each an internal resistance of 1*5 ohm, and an E.M.F. of 



1 -5 volt. Ans. 50 cells. 



12. You have 20 large Leclanche cells (E.M.F. = 1-5 volt, 

 ;'=O'5 ohm each) in a circuit in which the external resistance is 

 10 ohms. Find the strength of current which flows (a) when 

 the cells are joined in simple series ; (b} all the zincs are united, 

 and all the carbons united, in parallel arc ; (c) when the cells are 

 arranged two abreast (i.e. in two files of ten cells each) ; (d] 

 when the cells are arranged four abreast. 



Ans. (a) 1-5 iveber per sec. 

 (b) 0-1496 

 W i'2 

 (a) 0-702 ,, 



13. With the same battery how would you arrange the cells 

 in order to telegraph through a line 100 miles long, reckoning 

 the line resistance as 1 2 \ ohms per mile ? 



14. I have 48 cells, each of 1-2 volt E.M.F., and each of 



2 ohms internal resistance. What is the best way of grouping 

 them together when it is desired to send the strongest possible 

 current through a circuit whose resistance is 1 2 ohms ? 



Ans. Group them three abreast. 



15. Show that, if we have a battery of n given cells each of 

 resistance r in a, circuit where the external resistance is R, the 

 strength of the current will be a maximum when the cells are 

 coupled up in a certain number of rows equal numerically to 

 V nr -i- R. 



1 6. Two wires, whose separate resistances are 28 and 24, are 

 placed in parallel arc in a circuit so that the current divides, 

 part passing through one, part through the other. What resist- 

 ance do they offer thus to the current ? Ans. 12-92 o/ims. 



17. Using a large bichromate cell of practically no internal 

 resistance, a deflection of 9 was obtained upon a tangent 



*'*.*. lit ifi ^ 



