This is a proof type problem from our E&M class. We are given a point charge Q, let say that it is at the origin. We then have a disk parallel to the xy plane, with center a distance b from the origin( on the z axis) & radius R. We are to prove that if 1/4 of the flux passes thru the disk, prove that R= [(3)^.5]*b.(adsbygoogle = window.adsbygoogle || []).push({});

I assume that I have to use a spherical gaussian surface with 1/4 of its area corresponding to the size of the disk. Thats where I am confused. Do I make the top of the sphere just touch the bottom of the disk and have radius b, or do I construct it over the top of the disk, like a dome? And how do I acount for the fact that the electric feild lines wont be perpendicular to the surface of the disk because it is not round? Will this problem involve calculus, or is more of a geometry type problem?

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

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!

# Homework Help: Electric flux

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