In cosmic rays 0.15 protons `cm^(-2) s^(-1)` are entering the Earth's atmosphere . If the radius of the Earth is 6400 km, the current received by the Earth in the form of cosmic rays is nearly.

Options

A. `0.12 A`
B. `1.2 A`
C. `12 A`
D. `120 A`

Answer

A

Explanation

Surface area of the earth, `A = 4 pi r^(2)`
Charge entering the earth per second per unit area Current density (J).
`J = 0.15xx1.6x10^(-19)cm^(-2)s^(-1)`
`= 0.15xx1.6xx10^(-19)xx10^(4)m^(-2)s^(-1)`
`therefore` Current, `i=JA = J4 pi r^(2)`
`= 0.15xx1.6xx10^(-19)xx10^(4)xx4xx3.14xx(6.4xx10^(6))^(2)`
= 0.12 A