Electricity Lecture Notes

Importance of Electricity

• Essential in modern life.
• Used in homes, schools, hospitals, industries, etc.

Electric Components

• Electric Cell: Source of electric power.
• Electric Wire: Conducts electric current.
• Switch: Controls the flow of current (ON/OFF).
• Electric Bulb: Converts electric energy into light.

Electric Circuit

• A closed loop allowing electric current to flow.
• Circuit Completion:
  • OFF Switch: Circuit incomplete.
  • ON Switch: Circuit complete; electricity flows.
• Flow of electric energy = Electric Current.

Direction of Electric Current

• Conventional Current: Flow from positive to negative terminal.
• Electron Flow: Actual flow of electrons from negative to positive terminal.

Electric Current Formula

• Formula: I = Q / T
  • I = Current (Amperes), Q = Charge (Coulombs), T = Time (Seconds).

Units of Measurement

• Electric Charge:
  • SI unit: Coulomb (C).
  • 1 Coulomb = Charge of 6 x 10^18 electrons.
• Electric Current:
  • SI unit: Ampere (A).
  • 1 Ampere = 1 Coulomb/Second.
• Smaller Units:
  • Milliampere (mA) = 10^-3 A
  • Microampere (µA) = 10^-6 A.

Measuring Electric Current

• Ammeter: Measures current; connected in series.

Electric Potential

• Water tank analogy to explain potential:
  • Water flows from higher to lower potential.
• Voltage: Another term for potential difference.
• SI unit of voltage: Volt (V).
• Formula: 1 V = 1 J/C.
• Measured using a Voltmeter connected in parallel.

Electric Current Overview

• Electric current = Flow of electric charges.
• Example: Turning on a light switch creates a path for current to flow.

Electric Circuit Diagrams

• Use standard symbols to represent components:
  • Electric Cell, Battery, Switch (Open/Closed), Wire Joint, Electric Bulb, Resistors, Ammeter, Voltmeter.

Ohm's Law

• Proposed by George Simon Ohm.
• States: I is directly proportional to V and inversely proportional to R.
• Mathematical expression: V = IR or I = V/R.

Verifying Ohm's Law

• Use a circuit setup with multiple cells, ammeter, and voltmeter to plot V-I graph.
• Graph shows a straight line indicating V/I = constant (Resistance).

Resistance

• SI Unit: Ohm (Ω).
• Resistance definition: Opposition to electric current.
• Factors affecting resistance:
  1. Length of conductor.
  2. Cross-sectional area.
  3. Nature of the material.

Resistivity

• Property indicating how much a material resists electric flow.
• SI Unit: Ohm-meter.
• Low resistivity = good conductors (e.g., Copper, Aluminum).
• High resistivity = Insulators (e.g., Rubber, Glass).

Resistors in Series and Parallel

• Series:
  • Connected end-to-end.
  • Same current through each resistor.
  • Total resistance = Sum of individual resistances.
• Parallel:
  • Connected across the same two points.
  • Voltage same across all resistors.
  • Total resistance = Sum of reciprocals of individual resistances.

Heating Effect of Electric Current

• Resistance converts electrical energy into heat.
• Joule's Law: H = I²RT
  • Heat produced is proportional to the square of the current.

Applications of Joule's Law

• Electric Heaters: Convert electrical energy to heat.
• Electric Iron: Uses heat to press clothes.
• Fuses: Protect circuits by melting under high current.