Q. A beam contains $2 \times 10^{8}$ doubly charged positive ions per cubic centimeter, all of which are moving with a speed of $10^{5}\ m/s.$ The current density is
A) $6.4\ A/m^{2}$
B) $3.2\ A/m^{2}$
C) $1.6\ A/m^{2}$
D) None of these
Explanation
(a) $J = nqv = n(ze)v = \frac{2 \times 10^{8} \times 2 \times 1.6 \times 10^{- 19} \times 10^{5}}{\left( 10^{- 2} \right)^{3}} = 6.4A/m^{2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.