Coulomb's law

[Primarygun]

About Coulomb's law, it only works for a small test charge.

I am not perceptive of this part.

Does it works for a conductive sphere? I found many questions in my book employing this law to calculate the answer where it involves not only a small test charge but also a sphere.

[insane_alien]

does it? i've never seen anything about that. can you post a link?

 

I always seen it as an electrostatic version of newtons laws of gravity, in that they can work for large charges and spheres.

[swansont]

You can add the vectors of individual point charges, so you can scale up Coulomb's law. You can assume a charge density and integrate over the volume of the charge — each differential volume element will obey Coulomb's law, because it is essentially a point. You can also use a point approximation if the separation distance is significantly larger than the size of the particle.

 

There are examples of the particle-size correction in physics calculations, where e.g. a proton or nucleus is initially treated as a point particle and then a correction is made for its finite size.

[Klaynos]

IIRC for a spherical object applying gausses law to calculate the electric field (and therefore force) it simplifies to the coulomb interaction anyway.

[psynapse]

Well where it gets more complicated with insulating spherical shells and conducting spheres and such you can always take a Gaussian surface to calculate the charge or electric field using electric flux.