- #1
Crocodile
- 6
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Hi
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
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