Screenshot 2025-02-12 at 7.23-merged

Page 1: Current, Potential Difference, and Resistance

Current

• Definition: Current (I) is measured in amperes (A) and is the flow of charge at a point in a circuit.

• Formula: I = Q/t (where Q = charge in coulombs (C), t = time in seconds (s)).

• Types of Current:

  • In metals, current is the flow of electrons.

  • In solutions, current can be the flow of ions.

• Conventional Current: Defined as the flow of positive charge, opposite to the flow of negatively charged electrons.

• Conservation of Current: Current is conserved at a junction; charge is always conserved.

• Measurement: Current is measured with an ammeter connected in series with a component.

Potential Difference

• Definition: Potential difference (V) is measured in volts (V) and is the work done per unit charge moving between two points.

• Formula: V = E/Q.

• Measurement: Measured with a voltmeter placed in parallel across a component.

• Relationship with Current: Higher potential difference results in greater current (V = IR).

Resistance

• Definition: Resistance (R) is measured in ohms (Ω). It is defined as the potential difference across a component divided by the current through it: R = V/I.

• Impact of Resistance: Greater resistance makes it harder for current to flow.

• Ohmic vs Non-Ohmic Conductors:

  • Ohmic conductors: The current is directly proportional to voltage (constant resistance).

  • Non-ohmic conductors (e.g., filament lamps): Resistance changes with voltage/current.

Page 2: Characteristics of Components

Resistance Types

• Filament Lamp: As current increases, temperature rises causing increased resistance due to more electron-ion collisions.

• Thermistor: A resistor with resistance that decreases as temperature increases.

• Light-dependent Resistor (LDR): Resistance decreases as light intensity increases.

Types of Circuits

• Series Circuits:

  • Components are connected end-to-end.

  • Same current flows through each component.

  • Potential difference is shared; total voltage equals the sum across individual components.

  • Total resistance: R_total = R1 + R2 + R3...

• Parallel Circuits:

  • Components wired across common points (separate branches).

  • Current splits among branches; total current equals the sum in branches.

  • Voltage remains the same across each branch.

  • Advantageous for lamps, as failure of one does not affect others.

Page 3: Mains Electricity and Safety Hazards

Dangers of Electricity

• Hazards:

  • Damaged insulation can cause electric shocks.

  • Overheating cables due to high currents in thin wires can cause fires.

  • Damp conditions pose shock risks.

Safety Devices

• Fuses: Thin wire that melts to protect circuits from excessive current. Common ratings: 3A, 5A, 13A.

• Circuit Breakers: Automatically cut power for overloads, can be reset (faster than fuses).

• Earthing: Provides a safe route for current to flow during a short circuit, preventing shocks.

• Double Insulation: Uses non-conductive casings to prevent electric shocks.

Page 4: Energy Transfer and Power

Electrical Energy Transfer

• Energy Definition: Measured in joules (J), transferred from chemical energy in batteries to electrical energy and surroundings.

• Power Calculation: Power (P) in watts (W) calculated as P = IV, where V = IR leads to:

  • P = I²R,

  • P = V²/R.

• Energy Formula: E = IVt: Total energy transferred over time.

Current Types

• Direct Current (DC): Flows in one direction (e.g., batteries).

• Alternating Current (AC): Current changes direction periodically (e.g., mains electricity).

Page 5: Circuit Symbols

Common Electrical Symbols

• Battery, Diode, LED, Lamp, Resistors, Motor, etc.: Standard symbols for drawing electric circuits.

Page 6: Electric Charge

Charge Basics

• Measured In: Coulombs (C); protons (+1), electrons (-1), neutrons (0).

• Charging: Involves addition or removal of electrons, creating ions.

• Static Electricity: When insulators are rubbed together, electrons transfer, causing one material to gain a positive charge and the other a negative charge.

• Consequences: Build-up of static electricity seen in phenomena like lightning.

Page 7: Risks and Applications of Static Electricity

Dangers

• Electric Shock: High static charges can result in dangerous shocks.

• Fire Hazard: Sparks from electrostatic discharge can ignite flammable materials.

Applications

• Useful Applications:

  • Inkjet printers use charged ink droplets.

  • Photocopiers utilize static charge to transfer toner.

Page 8: Current, Voltage, and Resistance

Definitions

• Current (I): Flow of electric charge in a circuit (A).

• Voltage (V): Energy per charge (V).

• Resistance (R): Opposition to current flow (Ω) as per Ohm's Law: V = IR.

Page 9: Series and Parallel Circuits

Series Circuit Characteristics

• Same current throughout components.

• Total voltage equals sum of voltages across components.

• Total resistance is the sum of individual resistances.

Parallel Circuit Characteristics

• Voltage across each component remains the same.

• Total current is the sum of the currents in branches.

Page 10: Electric Power and Energy

Power Calculation

• Electric Power: Rate of energy transfer, P = IV (watts).

• Energy Consumption: Measured in kilowatt-hours (kWh), E = Pt.

Safety Measures

• Fuses, Circuit Breakers, Earthing, Double Insulation: Protect against electrical risks.

Page 11: Static Electricity

Static Electricity Characteristics

• Buildup of charge due to electron transfer; typically stationary until discharged.

Practical Applications and Risks

• Uses in various technologies (e.g., printers, photocopiers).

• Risks include sparks igniting flammable substances.