IV. Demonstration : Batteries. 



A battery is a group of two or more elements or cells 

 arranged to produce increased or multiple effect. If one 

 wishes to use a stronger current than that afforded by one 

 cell, his first thought is to increase the number of cells, or 

 to procure a larger cell. Experimentation will show him 

 that it is not a matter of indifference which of these courses 

 to pursue. In the first place if he attempts to satisfy the 

 conditions he will find that to increase the size of the cell 

 increases the current only when the external resistance is 

 relatively small, and furthermore, there are practical limi- 

 tations to the size of a cell and these may be much within 

 the requirement which the cells must satisfy. It be- 

 comes apparent, then, that he who would use electrical 

 energy beyond the most limited field must resort to a bat- 

 tery composed of a number of cells. The problem which 

 first confronts him is, how shall these cells be arranged 

 /. Appliances. 6 Daniel cells; wires; detector, (Fig. 6) 

 composed of simple magnetic needle mounted over 

 circle divided into degrees; rheostat or resistance box, 

 representing at least 100 ohms. 

 2. Experiments and Observations. 



(1) (a.) Join up apparatus as shown in Pi. I., Fig. 6. 

 With the plugs all fixed in the rheostat, i. e., 

 with no resistance except that of the wires and 

 battery, and the indicator needle at 0, open 

 the key and then observe the angle at which 

 the needle comes to rest. 



(b.) Remove from the rheostat the plug which will 

 throw into the circuit an extra resistance of 10 



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