The magnitude of the average electric field normally present in the earth's atmosphere just above the surface of the earth is about 150 N/C, directed downward. What is surface charge density of the earth? [Assume that the earth is a conductor having uniform surface charge density.]

Options

A. `+ 670 k C`
B. `- 670 k C`
C. `-680 kC`
D. `+680 kC`

Answer

C

Explanation

Given ,
Electric field E = 150 N/C
Total surface charge carried by eqrth q = ?
or, `q = in_(0) E A = in_(0) E pi r^(2)`
`= 8 . 85 xx 10^(-12) xx 150 xx (6 . 37 xx 10^(6))^(2) = 680 KC`
As electric field directed inward hence q = - 680 KC