Student "edition" found at {csi dot journalspace dot com}.

Maybe I shouldn't have started this blog now, not with everything that's been going on.

In the first session of my Introduction to Electricity and Magnetism lecture class for the third week of the first term, I finished the discussion on continuous charge distributions that we started the week before.

We had finished with the electrostatic force due to a uniform line of charge and a uniform ring of charge the meeting before, wherein I introduced the variable of lambda to represent the linear charge density or the charge per unit length.

For the ring, I had to tell them that the denominator of lambda is taken from the equation of the circumference of a circle.

Next we had the force due to a uniform disk of charge, for which I taught them sigma, the surface charge density or the charge per unit area. For this one, the area is the same as the area of a circle.

Then we went to a uniform sphere of charge, which of course used rho, the volume charge density or charge per unit volume. This required the volume of a sphere, dependent on the radius.

Lastly we had a uniform shell of charge, using sigma again, whose denominator is now the surface of a sphere. For both this and the previous scenario, the formula for the force is just the same as Coulomb's law, imagining the sphere or shell to have all its charge concentrated at a point in the center.

Additionally, I told them that for the shell, the force on any charge inside the shell is zero because all the forces from all the points around the charge will add up and cancel out.

After that we had several examples of the total charge on a particle from the combination of two continuous charge distributions, or one "subtracted" from another, as is the case with a disk with a hole.

Their first quiz is on the next meeting.

Session 1155 is inside the shell. Class dismissed.