Question

A point charge causes an electric flux of −1.0 × 10³ Nm²/C to pass through a spherical Gaussian surface of 10.0 cm radius centred on the charge.

1. If the radius of the Gaussian surface were doubled, how much flux would pass through the surface?
2. What is the value of the point charge?

Answer 1

(a) The electric flux passing through a spherical Gaussian surface drawn around a point charge does not depend on its radius, so even if the radius is doubled, the electric flux passing through it will remain −1.0 × 10³ N m²/C.

(b) Φ = `q/ε_0`

or q = Φ ε₀

or q = −1 × 10³ × 8.85 × 10⁻¹²

or q = −8.85 × 10⁻⁹ C

= −8.85 nC