Two spherical cavities of radii a and b are hollowed out from the interior of a neutral conducting sphere of radius R. At the center of each cavity is a point charge place, callthem qa and qb(adsbygoogle = window.adsbygoogle || []).push({});

a) Find teh surface charges sigma a, sigma b, and sigma R.

ok say for qa

[tex] \vec{E} = \frac{q_{a}}{4 \pi \epsilon_{0} a^2} \hat{a} = - \vec{\nabla} V \bullet \hat{n} [/tex]

also [tex] \sigma = -\epsilon_{0} \vec{\nabla} V \bullet \hat{n} = \frac{q_{a}}{4 \pi a^2} [/tex]

but i was told this answer should be negative.. where is my mistake?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Electric Field and spherical cavities

**Physics Forums | Science Articles, Homework Help, Discussion**