A current of 10 A exists in a wire of cross-sectional area of 5 ( mm ) 2 with a drift velocity of 2 × 1 0 − 3 ( m s ) − 1 . The number of free electrons in each cubic meter of the wire is

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i = 10 A , A = 5 ( mm ) 2 = 5 × 1 0 − 6 ( m ) 2 and v d ​ = 2 × 1 0 − 3 m s − 1 We know, i = n e A v d ​ ∴ 10 = n × 1.6 × 1 0 − 19 × 5 × 1 0 − 6 × 2 × 1 0 − 3 ⇒ n = 0.625 × 1 0 28 = 625 × 1 0 25

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