Current and Circuits - Summary Notes

Electric Current

• Electric current is a flow of charged particles.
• Conventional current is the direction a positive test charge moves.
• Electrons flow in the opposite direction of conventional current.

Electric Potential Difference

• Maintained by pumping charged particles from lower to higher potential.
• Requires an external energy source.
• Voltaic/Galvanic cells (batteries) convert chemical energy to electrical energy.
• Photovoltaic cells (solar cells) convert light energy to electrical energy.

Electric Circuits

• A closed loop allowing electric charges to flow.
• Includes a charge pump and a device that reduces potential energy.
• Charge is conserved; it cannot be created or destroyed.
• Energy is also conserved; change in electric energy (\Delta E = q\Delta V).

Rates of Charge Flow and Energy Transfer

• Electric current (I) is the rate of flow of electric charge: I = q/t.
• SI unit for current is the ampere (A): 1 A = 1 coulomb/second.
• Power delivered to a device: P = I\Delta V

Circuit Diagrams

• Use schematics with standard symbols (resistors, batteries, etc.) to represent circuits.

Resistance and Ohm’s Law

• Resistance (R) determines how much current flows.
• R = \Delta V/I, measured in ohms (Ω).
• One ohm (1 Ω) is the resistance permitting a current of 1 A with a potential difference of 1 V.
• Ohm’s law: Devices with constant resistance independent of potential difference.
• Resistors control current in circuits.
• Variable resistor (potentiometer) is used to control the current in circuits.

Parallel and Series Connections

• Parallel Connection: Current has multiple paths.
• Series Connection: Current has only one path.