Fig. 259.—Diagram of a Wheatstone bridge.
Important Topics
1. The internal resistance of voltaic cells.
2. Ohm's law applied to groups of cells. (a) Cells in series, (b) cells in parallel.
3. Measurement of resistance: (a) volt-ammeter method, (b) Wheatstone bridge method.
Exercises
1. What is the resistance of an electric bell circuit where the E.M.F. is 3 volts and the current is 0.6 ampere?
2. A telegraph wire is broken somewhere, the ends lying upon damp ground. If an E.M.F. of 30 volts is applied from the ground to the wire and a current of 0.1 of an ampere flows, what is the resistance of the part connected to the ammeter. (The earth which completes the circuit from the end of the wire has very small resistance.) Why?
3. How far away is the break in the wire if the latter has a resistance of 80 ohms to the mile? Diagram.