Lecture on Electricity

Basics of Electricity

• Electricity is a flow of electrons carrying energy from a source to a component.
• Batteries (or cells) store chemical potential energy, which is converted to electrical energy when the circuit is complete.
• Current: Flow of charge, moving from the positive terminal to the negative terminal of a battery.

Key Concepts

• Electrons: Transfer energy to components like bulbs, converting electrical energy into light.
• Charge: Measured in coulombs.

Potential Difference (Voltage)

• Voltage (PD): Energy transferred per coulomb of charge.
  • 1 Volt = 1 Joule/Coulomb
• Measured with a voltmeter (connected in parallel).
• Equation: ( V = \frac{E}{Q} )

Current

• Current (I): Rate of flow of charge, measured in amps (A).
  • Equation: ( I = \frac{Q}{T} )
• Measured with an ammeter (connected in series).

Resistance

• Resistance: Opposition to the flow of current.
• Components like bulbs and resistors have resistance, converting energy into light or heat.

Ohm's Law

• Equation: ( V = IR )
  • Resistance (R) from the slope of an IV graph.
• Ohmic: Resistors with constant resistance.
• Non-ohmic: Bulbs with changing resistance.

Circuit Components

• Diode: Allows current in one direction only.
• LED: Light-emitting diode, similar to a diode.
• Superconductor: Zero resistance below a critical temperature.

Resistivity

• Resistivity (( \rho )): Resistance of a unit cube of material.
  • Equation: ( \rho = \frac{RA}{L} )

Series and Parallel Circuits

• Series: Total PD shared, same current, sum of resistances.
• Parallel: Same PD across components, current divides, total resistance decreases.

Specialized Components

• Thermistor: Resistance decreases with temperature increase.
• LDR: Resistance decreases with light intensity increase.

Power

• Power: Rate of energy transfer.
  • Equation: ( P = VI )

AC and DC

• DC: Direct current, flows in one direction.
• AC: Alternating current, used for long-distance transmission.

Internal Resistance

• Internal Resistance: Resistance within a battery, causes some voltage drop.
• EMF: Total potential difference of a battery.

Semiconductors

• Used in thermistors and LDRs, number density affects conductivity.

Drift Velocity

• Drift Velocity: Speed of electron flow.
  • Equation: ( I = nAvq )