Answer:
Step-by-step explanation:
Potential at a point near a charge = Q / 4πε₀ R
where Q is charge given , R is distance of point from the charge .
Q / 4πε₀ R = 40
Electric field E at A = -dV / dR
= .16 x 10⁻³ / 2 x 10⁻⁶
= .08 x 10³
= 80 N/C
E = Q / 4πε₀ R²
80 = Q / 4πε₀ R x R
80 = 40 / R
R = 40 / 80
= .5 m .