Knowledge That Ignites
Original, Copyright-Free Notes aligned with Maharashtra Board syllabus
Complete coverage of heating, magnetic, and chemical effects of electric current
When electric current flows through a conductor, it produces various effects that have numerous practical applications in our daily life. Understanding these effects is crucial for both academic knowledge and practical implementation in electrical devices.
Electric current, which is the flow of electric charge, manifests itself in three primary ways that we study in this chapter. These effects form the basis for most electrical appliances and technologies we use today.
Production of heat when current flows through a conductor. Used in electric heaters, irons, toasters, etc.
Creation of a magnetic field around a current-carrying conductor. Used in electromagnets, electric motors, etc.
Chemical changes in substances when current passes through conducting liquids. Used in electroplating, electrolysis, etc.
Electric current is defined as the rate of flow of electric charges through a conductor. It represents how many charges are flowing per unit time through a cross-section of the conductor.
Where:
I
Used to represent electric current in equations and circuit diagrams.
Ampere (A)
Named after French physicist André-Marie Ampère, the SI unit of electric current.
One ampere of current flows when one coulomb of charge passes through a conductor in one second.
An electric circuit is a closed conducting path that allows electric current to flow. It provides a complete path for electrons to move from the source, through various components, and back to the source.
Closed circuit: Current flows, bulb lights up
Open circuit: Current doesn't flow, bulb remains off
Function: Source of electrical energy
Provides: Potential difference to drive current
Symbol: Long line (+) and short line (-)
Function: Conduct current between components
Material: Copper or aluminum (good conductors)
Insulation: Plastic or rubber coating for safety
Function: Opens or closes the circuit
Open position: Circuit broken, no current flows
Closed position: Circuit complete, current flows
Function: Converts electrical energy to other forms
Examples: Bulb (light+heat), resistor (heat), motor (motion)
Resistance: Offers opposition to current flow
| Aspect | Open Circuit | Closed Circuit |
|---|---|---|
| Switch Position | Switch is OFF/open | Switch is ON/closed |
| Current Flow | No current flows | Current flows continuously |
| Bulb Status | Bulb doesn't glow | Bulb glows (if circuit is complete) |
| Practical Example | Light switch turned OFF | Light switch turned ON |
Electric potential and potential difference are fundamental concepts that explain why electric current flows in a circuit. They represent the "electrical pressure" that drives charges through a conductor.
Definition: The amount of work done to bring a unit positive charge from infinity to a point in an electric field.
Analogy: Like height in gravity - gives potential energy per unit charge
Unit: Volt (V)
Definition: The work done to move a unit charge from one point to another.
Analogy: Like difference in height - causes water to flow
Unit: Volt (V)
Where:
1 Volt Definition: When 1 joule of work is done to move 1 coulomb of charge between two points, the potential difference is 1 volt.
Resistance is the opposition offered by a conductor to the flow of electric current. It converts electrical energy into heat energy. Every material (except superconductors) offers some resistance to current flow.
Relationship: Resistance is directly proportional to length
Formula: R ∝ L
Explanation: Longer conductor means more obstacles for electrons to overcome
Example: A 2m wire has twice the resistance of a 1m wire (same material and thickness)
Relationship: Resistance is inversely proportional to area
Formula: R ∝ 1/A
Explanation: Thicker wire provides more space for electrons to flow
Example: A wire with 2mm² cross-section has half the resistance of a 1mm² wire (same material and length)
Relationship: Different materials have different resistivities
Formula: R ∝ ρ (resistivity)
Good Conductors: Silver, copper, aluminum (low resistivity)
Insulators: Rubber, glass, wood (high resistivity)
For Metals: Resistance increases with temperature
For Semiconductors: Resistance decreases with temperature
For Alloys: Small change with temperature (used in heating elements)
Superconductors: Zero resistance at very low temperatures
Where:
Ohm's Law is a fundamental principle in electricity that describes the relationship between voltage, current, and resistance in an electrical circuit. It was formulated by German physicist Georg Simon Ohm in 1827.
"At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends."
Where:
Problem: A resistor has a resistance of 10 Ω. If a potential difference of 20 V is applied across it, what current flows through it?
Solution:
Using Ohm's Law: V = I × R
So, I = V / R = 20 V / 10 Ω = 2 A
Therefore, a current of 2 amperes flows through the resistor.
When we plot a graph of V (on y-axis) vs I (on x-axis) for an ohmic conductor (one that obeys Ohm's law):
When electric current flows through a device, it does work and consumes energy. Understanding electrical energy and power is essential for calculating electricity bills and designing electrical systems.
Definition: Energy consumed when electric current flows through a device
Formula: E = V × I × t
SI Unit: Joule (J)
Commercial Unit: kilowatt-hour (kWh)
Definition: Rate at which electrical energy is consumed
Formula: P = V × I
Unit: Watt (W)
Commercial Unit: kilowatt (kW)
Where:
Where:
| Unit | Definition | Conversion |
|---|---|---|
| 1 Watt (W) | 1 Joule per second | 1 W = 1 J/s |
| 1 kilowatt (kW) | 1000 Watts | 1 kW = 1000 W |
| 1 kilowatt-hour (kWh) | Energy consumed by 1 kW device in 1 hour | 1 kWh = 3.6 × 10⁶ J |
| 1 Horsepower (hp) | Approximately 746 Watts | 1 hp ≈ 746 W |
Problem: An electric bulb of 100 W is used for 5 hours daily. Calculate the energy consumed in 30 days and the cost if 1 kWh costs ₹5.
Solution:
When electric current flows through a conductor, the conductor gets heated. This phenomenon is called the heating effect of electric current. It occurs because electrons collide with atoms in the conductor, transferring kinetic energy as heat.
"The heat produced in a conductor is directly proportional to:
1. Square of the current (I²)
2. Resistance of the conductor (R)
3. Time for which current flows (t)"
Where:
Since V = I × R (Ohm's law), we can also write:
Heating element (nichrome wire) gets hot when current passes, used for ironing clothes.
Converts electrical energy to heat energy for room heating.
Heating element boils water quickly for making tea/coffee.
Heating wires toast bread by converting electrical energy to heat.
Tungsten filament gets so hot it emits light (only 10% efficient, 90% heat).
Safety device that melts when excess current flows, breaking the circuit.
Electrical safety is crucial to prevent damage to appliances, fires, and electric shocks. A fuse is an important safety device that protects electrical circuits from excessive current.
A fuse is a safety device that protects electrical appliances from damage due to excessive current. It consists of a short piece of thin wire made of a material with a low melting point (usually tin-lead alloy).
When current exceeds the rated value, the fuse wire heats up due to I²R heating, melts, and breaks the circuit.
Excess current can overheat and damage expensive electrical appliances. The fuse breaks the circuit before damage occurs.
Overheating of wires can cause insulation to melt and start fires. The fuse prevents this by breaking the circuit.
Prevents electric shocks that could occur from damaged appliances or short circuits.
| Type | Description | Common Use |
|---|---|---|
| Cartridge Fuse | Fuse wire enclosed in ceramic or glass cartridge | Industrial appliances, main supply |
| Kitchen Fuse | Fuse wire mounted on porcelain base | Household circuits |
| Automobile Fuse | Blade-type fuse with plastic body | Vehicles (cars, bikes) |
| Miniature Circuit Breaker (MCB) | Automatic switch that trips when excess current flows | Modern homes (replaces traditional fuses) |
When electric current flows through a conductor, it produces a magnetic field around it. This phenomenon is called the magnetic effect of electric current. It was discovered by Hans Christian Oersted in 1820.
Oersted observed that when a compass is placed near a current-carrying wire, the compass needle deflects. This proved that electric current produces a magnetic field.
An electromagnet is a temporary magnet made by winding a coil of insulated wire around a soft iron core. When current flows through the coil, it becomes magnetic. When current stops, it loses magnetism.
Electromagnet attracts iron armature which hits the gong, producing sound.
Electromagnets in cranes lift and move heavy iron objects in factories.
Electromagnetic switches used to control large currents with small currents.
Electromagnet interacts with permanent magnet to produce sound.
Powerful electromagnets levitate trains above tracks for frictionless travel.
Superconducting electromagnets produce strong magnetic fields for medical imaging.
Fleming's rules are simple hand rules used to determine the direction of force or induced current in electromagnetic systems. These rules are essential for understanding electric motors and generators.
Used for: Electric motors (force on current-carrying conductor)
Thumb: Force (Motion)
Index Finger: Magnetic Field
Middle Finger: Current
Hold your left hand with thumb, forefinger, and middle finger mutually perpendicular. Used to find direction of force on current-carrying conductor in magnetic field.
Used for: Electric generators (induced current)
Thumb: Motion of conductor
Index Finger: Magnetic Field
Middle Finger: Induced Current
Hold your right hand with thumb, forefinger, and middle finger mutually perpendicular. Used to find direction of induced current when conductor moves in magnetic field.
FLeMing's Left hand rule for Motor
The word "Left" and "Motor" both have 4 letters.
FLeMing's Right hand rule for Generator
The word "Right" and "Generator" both have more than 4 letters.
In an electric motor, Fleming's Left Hand Rule is used to determine the direction of rotation of the motor coil.
This force causes the coil to rotate, converting electrical energy to mechanical energy.
When electric current passes through a conducting liquid (electrolyte), it causes chemical changes. This phenomenon is called the chemical effect of electric current. It forms the basis of electrochemistry.
| Type | Definition | Examples | Current Conduction |
|---|---|---|---|
| Electrolytes | Substances that conduct electricity in molten state or aqueous solution and undergo chemical decomposition | Salt water, acid solutions, base solutions, copper sulfate solution | Yes (with chemical change) |
| Non-electrolytes | Substances that do not conduct electricity or do not decompose chemically when current passes | Distilled water, sugar solution, alcohol, kerosene | No or minimal |
Electrolysis is the process of chemical decomposition of an electrolyte by passing electric current through it.
Conducting liquid that undergoes decomposition (e.g., acidified water, copper sulfate solution)
Anode: Positive electrode (connected to positive terminal)
Cathode: Negative electrode (connected to negative terminal)
When current passes, electrolyte decomposes into ions. Positive ions move to cathode, negative ions move to anode.
Different substances deposit or collect at electrodes based on their chemical nature.
Observation: Gas bubbles form at both electrodes.
Test: Hydrogen burns with pop sound, oxygen relights glowing splinter.
Depositing a layer of one metal on another for protection or decoration.
Refining impure metals like copper to obtain pure metal.
Extracting reactive metals like aluminum, sodium from their ores.
Making printing plates by electrodeposition.
Charging process in lead-acid batteries involves electrolysis.
Electrolysis can be used to produce chlorine for water treatment.
Electroplating is the process of depositing a thin layer of one metal over another using electrolysis. It is one of the most important applications of the chemical effect of electric current.
Salt solution of the metal to be plated (e.g., copper sulfate for copper plating, silver nitrate for silver plating)
Made of pure plating metal (e.g., pure copper for copper plating)
Object to be plated (e.g., iron spoon for silver plating)
When current passes, metal from anode dissolves into electrolyte and deposits on cathode.
Coating prevents rusting/corrosion of base metal. Example: Chromium plating on car parts.
Making objects look attractive. Example: Gold/silver plating on jewelry.
Hard coatings protect against wear and tear. Example: Hard chromium plating on tools.
Tin plating on steel to make food cans that don't react with food.
Expensive metals like gold/silver can be plated on cheaper metals.
Silver plating on electrical contacts improves conductivity.
Ohm's Law:
Resistance:
Electrical Power:
Electrical Energy:
Joule's Law:
Current: