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

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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

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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

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2. Determine the current flowing through the wire

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

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

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Example 2: Aluminum Wire