Using gauss's law,calculate the electricfield at a distance r=20cm from a point charge q=4microcoulomb.

Answer 1

(Sphere area @ r) * (E field @ r)
= 4 pi k q

That is Gauss' Law in this situation, and reduces to:

4 pi r^2 * E(r) = 4 pi k q

E(r) = k q /r^2

which you might recognize as Coulomb's Law.

Plug in k and q values to get the E field in Volts/meter (or Newtons/Coulomb). Make sure r in in meters and q is in Coulombs. Look up the value of k if necessary.