RESISTANCE AND ELECTROMOTIVE FORCE. 57 



heating the circuit in accordance with Joule's Law. This matter may be stated in 

 another way, as follows : A certain portion of the observed electromotive force is 

 used to produce chemical action, and the remainder is used to overcome the re- 

 sistance of the electrolyte in accordance with Ohm's Law. The portion of the 

 electromotive force which is used to produce chemical action is about 2 or 2^ 

 volts, so that but little error is introduced by ignoring this effect and assuming that 

 the whole of the electromotive force is used to overcome resistance in accordance 

 with Ohm's Law. 



43. A coil of which the resistance is to be determined is con- 

 nected in series with an ammeter across iio-volt mains, and the 

 current is observed to be 26 amperes. What is the resistance of 

 the coil ? Ans. 4.23 ohms. 



44. A wire of which the resistance is 1 50 ohms is connected 

 to the terminals of a 1 1 o-volt dynamo, and a point on this wire 

 is grounded, the resistance between the positive terminal of the 

 dynamo and the grounded point being 60 ohms. Choosing the 

 ground as the region of zero potential, find the potential of each 

 terminal of the dynamo. Ans. The potential of the positive 

 terminal is + 40 volts, and the potential of the negative terminal 

 is 60 volts. 



45. A voltaic cell of which the electromotive force is 1.07 volts 

 and the resistance is 2.1 ohms is connected to a coil of 5 ohms 

 resistance, (a) What current is produced ? (b) What is the elec- 

 tromotive force drop in the cell ? (c) What is the electromotive 

 force between the terminals of the cell ? Ans. (a) o. 1 5 ampere, 

 (b) 0.32 volt, (e) 0.75 volt. 



46. A storage battery consisting of 54 cells connected in series 

 has a resistance of 0.0002 ohm per cell, and an electromotive 

 force per cell which ranges from 2 volts at the beginning to 1.85 

 volts at the end of the discharge. The battery supplies current 

 to 100 glow lamps (each having 220 ohms resistance) connected 

 in parallel between copper wires o. 3 2 5 inch in diameter at a dis- 

 tance of 200 feet from the battery. Find the electromotive force 

 between the terminals of the group of lamps at the beginning 

 and at the end of the discharge of the storage battery. Ans. 

 105.6 volts and 97.7 volts. 



