A uniform copper wire of length 1 m and cross-sectional area 0-5 mm² carries a current of I A. Assuming that there are 8 x 10²² free electrons per cm³ in copper, how long will an electron take to drift from one end of the wire to the other end?
Using the drift velocity formula vd = I/nAe’
where n = 8 × 10²⁸ electrons/m³,
A = 5 × 10⁸ m², and e = 1.6 × 10⁻¹⁹ C,
we get t = 6.4 × 10³ s Answer: (c).
Class 12th Science Physics NCERT MCQ Questions
NCERT Books MCQ Questions Session 2024-2025.
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Drift velocity is
vd = I/nAe , where n = 8 × 10²⁸
electrons/m³, A = 0.5 × 10⁻⁶ m²,
e = 1.6 × 10⁻¹⁹ C. Time t =
L/vd gives 6.4 × 10³ s. Answer: (c) 6.4 × 10³ s.
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