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Class 12
Physics
Current Electricity
the number density of free electrons in a copper c...

Question:
The number density of free electrons in a copper conductor estimated in Example 3.1 is 8.5 x 10²⁸ m^-3. How long does an electron take to drift from one end of a wire 3.0 m long to its other end? The area of cross-section of the wire is 2.0 x 10^-6 m² and it is carrying a current of 3.0 A.

Answer:

Number density of free electrons in a copper conductor, n = 8.5 × 10²⁸ m ^{- 3} Length of the copper wire, l = 3.0 m

Area of cross-section of the wire, A = 2.0 × 10 ^{- 6} m²

Current carried by the wire, I = 3.0 A, which is given by the relation,

I = nAeV_d

Where,

e = Electric charge = 1.6 × 10 ^{- 19} C

V_d = Drift velocity

Therefore, the time taken by an electron to drift from one end of the wire to the other is 2.7 × 10⁴ s.

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Question: The number density of free electrons in a copper conductor estimated in Example 3.1 is 8.5 x 1028 m-3. How long does an electron take to drift from one end of a wire 3.0 m long to its other end? The area of cross-section of the wire is 2.0 x 10-6 m2 and it is carrying a current of 3.0 A.

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