Question

The magnitude of momentum of electrons in a straight wire of copper of length1 meter carrying a current of 16 ampere will be

• A. 14.56 × 10⁻¹² kg msec⁻¹
• B. 29.12 × 10⁻¹² kg m sec⁻¹
• C. 18.2 × 10⁻¹¹ kg m sec⁻¹
• D. 91 × 10⁻¹² kg m sec⁻¹

Answer 1

Answer: (D)

91 × 10⁻¹² kg m sec⁻¹

Answer 2

If n is the number of electrons per unit volume, then total number of free electrons = nLA

Hence total mass of the electrons = nLA m_e

Total momentum of electrons = nLA m_e × v_d = nLA m_e × $\frac { \mathrm { l } } { \mathrm { e } }$

= $\frac { 1 \times 9.1 \times 10 ^ { - 31 } \times 16 } { 1.6 \times 10 ^ { - 19 } }$ = 91 × 10⁻¹² kg- sec⁻¹, Hence correct answer is