Finding Centre of Hemisphere - Radius a

[latentcorpse]

imagine a hemisphere of radius a with the circle lying in the x-y plane and so the axis of the hemisphere is the z axis. if z=0 is at the centre of our circle, what value of z corresponds to the centre of the hemisphere?

i used z=a/2 but have a sneaky feeling its' meant to be $\frac{a}{\sqrt{2}}$

can anyone help?

 

[Russell Berty]

Do you want the CENTER OF MASS?

Are you looking at the top half of a solid sphere centered at the origin with radius a?

 

[latentcorpse]

i don't want the centre of mass. yes your talking about the right shape.

basically i have an expression for the electric field on the z axis as the hemispherical surface is charged and it asks me to find the value of the electric field at the centre of the hemisphere - what z value should i use?