# Understand Ohm`s law in both microscopic

Magnetostatics:

Understand Ohm’s law in both microscopic (

J

E

)

and macroscopic (

V

IR

) form. Have an understanding of why

J

and

E

are related in this way. Given a resistor of cross-sectional area

A

and length

l

, be able to derive the formula

R

.

Understand what

2

I R

means in (ohmic dissipation). q

V

x

B

force: be able to compute this direction; be able to derive the cyclotron frequency, the relations between v,

,

T

, and R for a particle moving in a circle. Be able to correctly get the sense of revolution of a charge in a given constant magnetic field given the field direction and the charge of the particle.

F

I

: be able to compute this direction, and understand the meaning of it, e.g. for a current loop above a magnet.

Biot Savart Law: be able to use to calculate the magnetic field from simple current elements, e.g. the magnetic field at the center of a circle of radius

R

carrying current

I

.

Magnetic dipole moment: what is it, how is it directed, what is its magnitude?

Torque on a magnetic dipole

τ

 

.

What does it mean, e.g. what direction does it cause a compass needle in a background field to rotate, how does it arise, and so on.

Ampere’s Law: be able to find the magnetic field using Ampere’s Law in situations with a high degree of symmetry. There are a few problems here: planes of current, field inside a solenoid, problems with cylindrical symmetry.