8.02 Lecture Notes - Lecture 1: Drift Velocity, Electric Potential
Document Summary
When a current ows in a wire of length l and cross sectional area a, the resistance of the wire is proportional to length and inversely proportional to area. Average current is equal to the charge q owing across area a at time t. Instantaneous current is the differential limit of the average current. Direction of current is in the direction of the ow of positive charge. You can also think of it as the opposite of ow of negative charge. If an electric eld is set up in a conductor, charge will move, making a current in the direction of e. Drift velocity is the average velocity forced by applied electric eld in the present of collisions. The current density is current per unit area. Current is the ow ( ux) of current density through an open surface. Special case: j uniform and perpendicular to the surface.
