8. (a) Compare the diameters of No. 22 and No. 16 copper wire.
(b) Compare the lengths of the same wires giving 1 ohm resistance.
(c) What relation exists between (a) and (b)?
9. Why is an electric bell circuit usually open while a telegraph line circuit is usually closed?
10. A copper wire and an iron wire of the same length are found to have the same resistance. Which is thicker? Why?
11. Why are electric bells usually arranged in parallel instead of in series?
12. What would happen if a voltmeter were put in series in a line?
(3) Ohm's Law and Electrical Circuits
271. Conditions Affecting Current Flow.—Sometimes over a long circuit one cell will not work a telegraph sounder. In such a case, two, three, or more cells are connected so that the zinc of one is joined to the copper plate of the other. When connected in this way the cells are said to be in series (Fig. 251). In the figure A represents a voltmeter. It is found that when cells are in series the E.M.F. of the battery is the sum of the electromotive forces of the cells. An ammeter in the circuit shows increased current as the cells are added. Hence if the resistance of the circuit remains unchanged, the greater the E.M.F. the greater is the current strength. In this respect, the movement of electricity in a circuit is similar to the flow of water in a small pipe under pressure, as in the latter the flow of water increases as the pressure becomes greater. The current in a circuit may also be increased by lessening the resistance, since the current through a long wire is less than that through a short one, just as the flow of water will be greater through a short pipe than through a long one. To increase the current flowing in an electric circuit, one may therefore either increase the E.M.F. or decrease the resistance.