*The problem statement(adsbygoogle = window.adsbygoogle || []).push({});

The second question kinda builds on the first and I am not too confident my solution to the first is correct.

1: A disk has a uniform surface charge density and is rotated at a rate 'w'. Find 'K'.

2: A uniformly charged sphere ('ρ') is spun. Find the current density.

*Relevant equations

K=surface current density = σ*v

J = volume current density = ρ*v

*The attempt at a solution

1: ω= the linear (tangental?) velocity of a point on this disk / radius, so v=wr

then K = ωr*σ , and is oriented in the ∅ direction

2: for a spinning sphere, the velocity of the charge is the same as above except v=0 on the axis of rotation for any r.

so if i let the z axis be the axis of rotation, and let r = r(cos∅+sin∅), and v=wr(cos∅+sin∅)

then J = ρwr(cos∅+sin∅), oriented in ∅ direction

yea thats my attempt at the solution. I think my answers make sense, but most homework problems I am assigned require more than 2 lines of work so it is not unlikley that i am missing something.

thanks in advance for any help

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# Homework Help: Two closely related questions about current density

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