Question

A beam of electrons moving at a speed of 10⁶m/s along a line produces a current of 1.6 × 10^–6A. The number of electrons in the 1 metre of the beam is

• A. 10⁶
• B. 10⁷
• C. 10¹³
• D. 10¹⁹

Answer 1

Answer: (B)

10⁷

Answer 2

$i = \frac { q } { t } = \frac { q } { ( x / v ) } = \frac { q v } { x } = \frac { n e v } { x }$

⇒ $n = \frac { i x } { e v } = \frac { 1.6 \times 10 ^ { - 6 } \times 1 } { 1.6 \times 10 ^ { - 19 } \times 10 ^ { 6 } } = 10 ^ { 7 }$