Hi(adsbygoogle = window.adsbygoogle || []).push({});

Im getting a slightly different answer to the one that is needed for the following question:

2) A positive charge Q is distributed throughout a spherical volume of radius R in vacuum.

The charge density rho varies with the radius according to the linear law rho = a r. Show that the parameter a is Q/(pi R^4).

I started by saying that I'm looking at the position where r=R, i.e. at the surface itself. At this point the total charge Q must be present. Hence Q= rho x volume = a x r x volume, and as R=r Q= a x R x volume. Therefore Q = a x r x (4/3)pi R^3, which gives an a similar to the one required, but multiplied by 3/4.

Any ideas where I am going wrong?

Thanks

**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!

# Homework Help: Gauss law question

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