Topic: Electric Current and Electrical Energy PSSA: C / S8.C.2.1

Objective:  TLW describe electric current.  TLW describe voltage and resistance and their relationship to electric current.

MI #1: Electric Current  An electric current is the rate at which a charge passes a given point.  The higher the current, the greater the number of charges that pass a point in a given second.  Electric current is measured in amperes (or amps) A.

MI #2: AC/DC  With Alternating Current (AC), the flow of charge continually changes direction.  With Direct Current (DC), the charge always flows in the same direction.  Electrical current in your home is AC and electrical current from batteries is DC.

MI #3: Voltage  Voltage is the potential difference between two points in a circuit, measured in Volts (V).  It is a measure of how much work is needed to move a charge between two points.  The greater the voltage, the greater the current.

MI #4: Resistance  Resistance is the opposition to the flow of electric charge, measured in Ohms (Ω).  Resistance is like “electrical friction.”  Good conductors have low resistance, while poor conductors have high resistance.  Thicker wire has les resistance than thin wire.

Mi #5: Resistance and Temperature  As a general rule, the resistance of material rises with temperature.  Atoms vibrating at faster rates (due to higher temperatures) get in the way of flowing electrons.  Some materials show no resistance (0 Ω) when cooled to extremely low temperatures; these are called superconductors.

MI #6: Electrical Cells  Cells (in electricity) are devices that produce an electrical current by converting chemical or radiant energy into electrical energy.  Cells contain electrolytes, which allow the charge to flow, and electrodes, which allow the charge to enter and exit.  Chemical changes between the electrolyte and electrodes convert the chemical energy into electricity.

So What…? Real Life Application  Understanding current, voltage, and resistance is important to understanding why some materials are better conductors than others.