Question

A electric current of 16 A exists in a metal wire of cross section 10⁻⁶ m² and length 1m. Assuming one free electrons per atom. The drift speed of the free electrons in the wire will be (Density of metal =5 × 10³ kg/m³, atomic weight = 60)

• A. 5 × 10⁻³ m/s
• B. 2 × 10⁻³ m/s
• C. 4 × 10⁻³ m/s
• D. 7.5 × 10⁻³ m/s

Answer 1

Answer: (B)

2 × 10⁻³ m/s

Answer 2

According to Avogadro's hypothesis $\frac { N } { N _ { A } } = \frac { m } { M }$

so n = N_A $\frac { m } { V M } = \frac { N _ { A } } { M }$

Hence total number of atoms n = $\frac { 6 \times 10 ^ { 23 } \times 5 \times 10 ^ { 3 } } { 60 \times 10 ^ { - 3 } }$ = 5 × 10²⁸ /m³

Hence drift velocity v_d =

=$\frac { 16 } { 5 \times 10 ^ { 28 } \times 1.6 \times 10 ^ { - 19 } \times 10 ^ { - 6 } }$
= 2 × 10⁻³ m/s. Hence correct answer is