Electricity

• Electricity is the flow of charge or charges like electrons that carry energy from a source of energy to a component
• A battery has a store of chemical potential energy that is transferred to the electrons when connected in a complete circuit
• The movement of charge is called a current and it always goes from the positive terminal of the battery to the negative
• Potential difference (PD) or voltage tells us how much energy is transferred per unit of charge
• Resistance in components resists the flow of charge through them
• Ohm's Law: V = IR, where V is voltage, I is current, and R is resistance
• Resistance can be calculated from an IV graph by picking a point on the line and rearranging Ohm's Law
• Metals have a changing resistance due to collisions between electrons and ions as current flows through them
• A diode only lets current flow in one direction, while an LED emits light and acts as a diode
• A superconductor has zero resistance at or below a critical temperature
• Resistivity is the resistance of a cube of unit length sides of a material
• In series circuits, total PD is shared, current is the same, and resistance is the sum of all resistances
• In parallel circuits, PD is the same for every branch, current is shared, and total resistance decreases as more resistors are added
• A thermistor's resistance decreases with increased temperature, while an LDR's resistance decreases with increased light intensity
• Power is the rate of energy transferred, calculated as P = VI
• Batteries have internal resistance, which causes a loss of voltage known as terminal PD
• Semiconductors have electrons that need enough energy to move from the valence band to the conduction band to conduct electricity
• Drift velocity is the speed of an electron as it flows through a wire