Two concentric conducting spherical shells of radii $a$ and $b$ ($b > a$) carry charges $+Q$ and $-Q$ respectively. The electric field at a distance $r$ from the center, where $a < r < b$, is:

Consider a thin spherical shell of radius $R$ consisting of uniform surface charge density $\sigma$. The electric field at a point of distance $x$ from its centre and outside the shell is

Two concentric conducting spherical shells of radii $a$ and $b$ ($b > a$) carry charges $+Q$ and $-Q$ respectively. The electric field at a distance $r$ from the center, where $a < r < b$, is: