# Electric Current

• Electric current is the flow rate of electric charge

• Units are C/s, or amperes (A)

• Positive current flow is the direction of the flow of positive charges, which is opposite the direction of electron flow

• # Drift Velocity

• In a conductor, electrons are inconstant thermal motion.

• Net electron flow, however, is zero because the motion is random

• When an electric field is applied, a small net flow in a direction opposite the electric field is observed

• # Derivation of Current Flow  # Current Density

•   # Resistance

• Resistance is the ratio of the potential drop across an object to the current flowing through the object.

• Object which have a fixed resistance (not a function of current of potential drop) are known as Ohmic materials and are said to follow Ohm's Law (an empirical law) # Resistance of a Wire

• The resistance of a wire depends on the geometry of the wire as well as a material property known as resistivity ⍴ (Unit: Ω·m)

• Resistivity relates to the ability of a material to resist the flow of electrons # Refining Ohm's Law

• • • • # Conversion of Electric Energy to Thermal Energy

• • • # Example 1: Silver Wire

• 1. Determine the resistance of the wire

• 2. Determine the current flowing through the wire

• 3. Determine the drift velocity of the free electrons in the wire (assume one free electron per atom)

• • • 4. Determine the average time required for electrons to pass from the negative terminal of the battery to the positive terminal

• # Example 2: Aluminum Wire

• • 