Physics: Electric Current

Rate Quantity

• Current is a rate quantity, mathematically expressed as a quantity over time.
• The symbol I represents current.
• The standard metric unit for current is the ampere (A), where 1 ampere = 1 coulomb / 1 second.

Conventional Current Direction

• The direction of an electric current is conventionally the direction that a positive charge would move.
• Electrons are the charge carriers in metal wires, but they move in the opposite direction of the electric field.
• The convention of current direction was established by Ben Franklin, who envisioned positive charges as the carriers of charge.

Electric Potential Difference

• Electric potential is a location-dependent quantity that expresses the amount of potential energy per unit of charge at a specified location.
• Electric potential difference is the difference in electric potential between two points.
• The standard metric unit for electric potential difference is the volt (V), where 1 volt = 1 joule / 1 coulomb.

Electric Potential Difference and Circuits

• Electric potential difference is the energy required to move a charge between two locations.
• A battery supplies the energy to do work upon the charge to move it from the negative terminal to the positive terminal.
• The movement of charge through an electric circuit is analogous to the movement of water at a water park or the movement of roller coaster cars at an amusement park.

Circuit Elements

• Circuit elements serve as energy-transforming devices.
• Examples of energy-transforming devices include light bulbs, motors, and heating elements.
• In each device, the electrical potential energy of the charge is transformed into other useful (and non-useful) forms.
• The moving charge is doing work upon the circuit element to produce different forms of energy.
• The location just prior to entering the circuit element is a high electric potential location, and the location just after leaving the circuit element is a low electric potential location.
• The loss in electric potential while passing through a circuit element is often referred to as a voltage drop.