A potentiometer wire has length 4 m and resistance 8 Ω. The resistance that must be connected in series with the wire and an accumulator of e.m.f. 2 V, so as to get a potential gradient 1 mV per cm on the wire is
32 Ω
40 Ω
44 Ω
48 Ω
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The Kirchhoff’s first law (Σi = 0) and second law (ΣiR = ΣE), where the symbols have their usual meanings, are respectively based on