Question

An electric charge q is placed at one of the corner points of a cube of side a. What will be the net outwards flux coming out of the cube due to the point charge?

(a) \(\frac {q}{\varepsilon_o}\)

(b) \(\frac {q}{2\varepsilon_o}\)

(c) \(\frac {q}{4\varepsilon_o}\)

(d) \(\frac {q}{8\varepsilon_o}\)

The question was asked by my school principal while I was bunking the class.

This key question is from Gauss’s Law topic in portion Charges and Fields of Physics – Class 12

Answer 1

The correct choice is (d) \(\frac {q}{8\varepsilon_o}\)

To explain: We can assume 8 imaginary cubes, all of side a placed together, sharing a common corner point and forming a bigger cube of side 2a. The point charge is placed at the common point of the cubes. According to Gauss’s Law, net electric flux coming out of the bigger cube=\(\frac {q}{\varepsilon_o}\). Therefore, flux coming out from each of the smaller cubes i.e. cubes of side a is \(\frac {q}{8\varepsilon_o}\).