Register your clicker

Go to https://www1.iclicker.com/register-clicker/ and register your clicker.

Inside this resistor setup, what can you conclude about the current density $\mathbf{J}$ near the side walls (in steady state)?

1. Must be exactly parallel to the wall
2. Must be exactly perpendicular to the wall
3. Could have a mix of parallel and perp components
4. No obvious way to decide!?

Activity: Consider two spheres (radii $a$ and $b$ with $b$>$a$) that are constructed so that the larger one surrounds the smaller one. Between them is a material with conductivity $\sigma$. A potential difference of $V$ is maintained between them with the inner sphere at higher potential.

• What is the current $I$ flowing between the spheres in terms of the known variables?
• How does your result relate to Ohm's Law?

Hint: Assume a uniform charge $+Q$ distributed over the inner sphere and use Gauss' Law to find $\mathbf{E}$.