Question

The region between two concentric spheres of radius a < b contain volume charge density r(r) = $\frac{c}{r}$, where c is constant and r is radial distance, as shown in figure. A point charge q is placed at the origin, r = 0. Value of c is in such a way for which the electric field in the region between the spheres is constant (i.e. independent of r). Find the value of c –

• A. $\frac{q}{2\pi a^{2}}$
• B. $\frac{q}{4\pi a^{2}}$
• C. $\frac{q}{\pi a^{2}}$
• D. $\frac{q}{a^{2}}$

Answer 1

Answer: (C)

$\frac{q}{\pi a^{2}}$

Answer 2

f_total = 10 + 30 + 20 – 15 = 45