Question:

If an insulated non-conducting sphere of radius $R$ has charge density $ \rho . $ The electric field at a distance r from the centre of sphere $(r > R)$ will be:

Updated On: May 22, 2024
  • $\frac{\rho R}{3 \varepsilon_{0}}$
  • $\frac{\rho r}{\varepsilon_{0}}$
  • $\frac{\rho r}{3 \varepsilon_{0}}$
  • $\frac{3 \rho R}{\varepsilon_{0}}$
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The Correct Option is C

Solution and Explanation

Charge which is enclosed in the surface is given by
$\sigma=\frac{4}{3} \pi r^{3} \rho$
Now according to Gaussian law
$\varepsilon \,\phi\, E d s=\sigma,$
$ \varepsilon_{0} E 4 \pi r^{2}=\frac{4}{3} \pi r^{3} \rho $
$E=\frac{\rho r}{3 \varepsilon_{0}}$
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Concepts Used:

Electric Field

Electric Field is the electric force experienced by a unit charge. 

The electric force is calculated using the coulomb's law, whose formula is:

\(F=k\dfrac{|q_{1}q_{2}|}{r^{2}}\)

While substituting q2 as 1, electric field becomes:

 \(E=k\dfrac{|q_{1}|}{r^{2}}\)

SI unit of Electric Field is V/m (Volt per meter).