 The continuous flow of electrons is current.  Measured in amps (A).  Two types of current 1. Direct current (DC) – electrons flow in only one direction. 2. Alternating Current (AC) – flow of electrons keeps switching directions.

 Electrons flow due to a difference in electrical potential energy (EPE) of charges ◦ Charges flow from higher potential energy to lower potential energy ◦ Potential difference, or Voltage, is the difference of EPE between two places in an electric field.

 Electrons flow due to a difference in electrical potential energy (EPE) of charges ◦ Voltage is measured in volts (V), which are joules per coulomb. ◦ The greater the voltage, the greater the “push” on the electrons.

 As electrons flow through materials, they collide with other electrons and ions, losing energy and slowing current.  This opposition to flow of electricity in a materials is its resistance.  Anything that electricity flows through has resistance.

 Measured in ohms (Ω).  Resistance of a material is affected by its: 1. Thickness: thicker = less resistance 2. Length: Longer = more resistance 3. Temperature: Warmer = more resistance

 Resistance, current and voltage are related (Ohm’s Law):  I = current, V = Voltage, R = resistance IR V

 Example 1) What is the resistance of a headlight that draws 3.0 A of current from a 12 V battery?  Example 2) What is the voltage needed to produce a current of 3 amps through 3 Ω?  Example 3) What is the current running through 6 V battery connected to a light bulb with a resistance of 1.5 Ω?

 Conductors have low resistance and insulators have high resistance.  Semiconductors will conduct electricity in certain situations  Superconductor is a material that has almost zero resistance when cooled to low temperatures.