Question

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.

• A. $0.12\, A$
• B. $1.2\, A$
• C. $12\, A$
• D. $120\, A$

Answer 1

Answer: (A)

Surface area of earth, $A=4\pi r^{2}$
Charge entering the earth per sec per unit area
$J=0.15\times1.6\times10^{-19}\,C\,cm^{-2}s^{-1}$
$=0.15\times1.6\times10^{-19}\times10^{4}\,C\,m^{-2}s^{-1}$
Current $I=JA=J\,4\pi r^{2}$
$=0.15\times1.6\times10^{-19}\times10^{4}\times4\times3.14\times\left(6.4\times10^{6}\right)^{2}$
$=0.12\,A$.