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Table 12.1 Symbols of some commonly used components in circuit diagrams, , Es ae ee, , 1 An electric cell — -—, 2 A battery or a combination of cells — al tr aes, , al Plug key or switch (open) + ke, 4 Plug key or switch (closed) —(e}—, , 5 A wire joint, , +, , 6 — Wires crossing without joining, , 7 Electric bulb Oo ¥, 8 A resistor of resistance R —AVI//—_, , 9 Variable resistance or rheostat yi or }, , 10 Ammeter, , 11 Voltmeter, , 12.4 OHM’S LAW, , Is there a relationship between the potential difference across a, conductor and the current through it? Let us explore with an Activity., , Activity’ 12.1, , = Set up a circuit as shown in Fig. 12.2, consisting of a nichrome wire XY of length, say 0.5 m,, an ammeter, a voltmeter and four cells of 1.5 V each. (Nichrome is an alloy of nickel, chromium,, manganese, and iron metals.)