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The number of free electrons per 10 mm of ordinary copper wire is about 2×1021. The average drift speed of the electrons is 0.25 mm s-1. The current flowing is:-

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Important Questions on Current Electricity

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Two wires each of radius of cross section r but of different materials are connected together end to end (i.e., in series). If the densities of charge carriers in the two wires are in the ratio 1:4, the drift velocity of electrons in the two wires will be in the ratio
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A current I flows through a uniform wire of diameter d, when the mean drift velocity is V. The same current will flow through a wire of diameter d2 made of the same material. If the mean drift velocity of the electrons is-
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A wire has a non-uniform cross-section as shown in the figure. A steady current flows through it. The drift speed of electrons at points P and Q is vP and vQthen:-

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When a potential difference is applied across the ends of a linear metallic conductor :-
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Assertion :- In a metallic conductor, current is due to the drift of free electrons in a definite direction.

Reason :- A current carrying conductor is negatively charged.

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There are two wires of the same length and of the same material and radii r ạnd 2r. The ratio of their specific resistance is 
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Consider four conducing materials copper, tungsten, mercury and aluminum with resistivity ρC, ρT, ρM and ρA respectively. Then :
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The length of germanium rod is 0.925 cm and its area of cross section is 1 mm2. If for germaniun ni= 2.5×1019 m-3,μh=0.19 m2/v-s,μe=0.39 m2/v-s, then the resistance of the rod is