A hollow metallic sphere of radius R is charged to a surface density of σ. The strength of the electric field inside the sphere at a radius r(< R) is
1
\(\frac{\sigma }{\pi {{r}^{2}}}\)
2
\(\frac{\sigma }{2\pi {{r}^{2}}}\)
3
\(\frac{\sigma }{4\pi {{r}^{2}}}\)
4
Zero