Magnetic Effect Of Electric Current Notes

MG SCHOOL SCIENCE • CLASS 10

Magnetic Effects of Electric Current

Chapter Notes • Important Concepts • Rules • Quick Revision • Self-Test

📚 Quick Navigation

1. Introduction and magnets 2. Properties of magnets 3. Magnetic field and field lines 4. Straight conductor 5. Circular loop 6. Solenoid 7. Force on a conductor 8. Medical applications 9. Domestic electric circuits 10. Quick revision 11. Self-test MCQs

1. Introduction to Magnetism

What is a magnet?

A magnet is a material that generates a magnetic field and can attract or repel materials with magnetic properties. Examples of magnetic materials include iron, nickel and cobalt. Lodestone is a natural magnet.

• Every magnet has two poles: north and south.
• Magnetic poles always occur in pairs and cannot be separated.
• A freely suspended magnet aligns approximately in the north–south direction.

Electric current and magnetism

An electric current-carrying wire behaves like a magnet. A compass needle gets deflected when electric current passes through a metallic conductor.

Electromagnets and electric motors involve the magnetic effect of electric current. Electric generators involve the generation of electric current by moving magnets.

Bar magnet

A bar magnet is a solid, typically rectangular object made from a magnetic material such as iron or steel. It has two distinct poles: north and south. Its north pole points approximately towards the Earth's geographic north when freely suspended. This property is useful in magnetic compasses.

NORTH (N)← attraction / repulsion →SOUTH (S)

2. Properties of Magnets

1. Every magnet has two poles: North and South.
2. Like poles repel each other.
3. Unlike poles attract each other.
4. A freely suspended bar magnet aligns itself approximately in the north–south direction, with its north pole towards the north.

N↔NLike poles repel

N→←SUnlike poles attract

3. Magnetic Field and Field Lines

Magnetic field: A magnetic field is a vector quantity; it has both magnitude and direction. Its direction at a point is indicated by the direction in which the north pole of a compass needle points at that point.

Characteristics of magnetic field lines

• Outside a magnet, field lines emerge from the north pole and enter the south pole.
• Inside the magnet, field lines go from south to north, forming continuous closed loops.
• The closeness of field lines indicates field strength. Closer lines represent a stronger magnetic field.
• Magnetic field lines never intersect. If they intersected, a compass needle at the intersection would have to point in two directions at once.

Remember the direction:
Outside the magnet: North → South
Inside the magnet: South → North

Oersted's discovery

H. C. Oersted was the first person to demonstrate that an electric current produces a magnetic field.

A magnetic field can be thought of as an invisible region around a magnet or current-carrying conductor where magnetic force can be experienced.

4. Magnetic Field Due to Current Through a Straight Conductor

• The magnetic field around a straight current-carrying conductor forms concentric circles centred on the wire.
• The direction of the field can be found using the Right-Hand Thumb Rule or a magnetic compass.
• The circles are closer together near the conductor, showing that the field is stronger near the wire.
• Increasing the current increases the magnetic field strength and the compass needle's deflection.
• Moving the compass farther from the wire decreases the needle's deflection when current is constant.

Magnetic field strength ∝ Current

Magnetic field strength ∝ 1 / Distance from conductor

Right-Hand Thumb Rule

Imagine holding a current-carrying straight conductor in your right hand so that your thumb points in the direction of current. The curled fingers give the direction of the magnetic field lines around the conductor.

Thumb
Direction of current

➜

Curled fingers
Direction of magnetic field

5. Magnetic Field Due to Current Through a Circular Loop

• The magnetic field around a circular loop varies with distance.
• Near the centre of the loop, the magnetic field lines appear as straight lines.
• At the centre, the magnetic field contributions from each part of the wire are in the same direction and add together.
• If a coil has multiple turns, the magnetic field becomes stronger because the field due to each turn adds up.

Factors affecting the magnetic field of a circular current-carrying coil

Factor	Relationship stated in the notes
Current through the conductor	Magnetic field ∝ Current
Radius of the coil	Magnetic field ∝ 1 / Radius
Number of turns	Magnetic field ∝ Number of turns
Multiple loops	Fields due to the loops add together when current flows in the same direction in each turn.

6. Magnetic Field Due to Current in a Solenoid

Solenoid: A solenoid is a coil made of many circular loops of insulated copper wire wrapped tightly in a cylindrical shape.

• One end of a current-carrying solenoid acts like a north pole and the other like a south pole.
• The magnetic field pattern of a solenoid resembles that of a bar magnet.
• Inside the solenoid, magnetic field lines are straight and parallel, indicating a uniform magnetic field.
• A solenoid can magnetise a soft iron material placed inside it, forming an electromagnet.

Direction of field:
Outside the solenoid: North → South
Inside the solenoid: South → North

7. Force on a Current-Carrying Conductor in a Magnetic Field

• André-Marie Ampère (1775–1836) proposed that if a current-carrying conductor produces a magnetic field and exerts a force on a magnet, the magnet must also exert an equal and opposite force on the conductor.
• When an aluminium rod carrying electric current is placed in a magnetic field, it experiences a mechanical force and gets displaced.
• Reversing the current reverses the direction of force.
• Reversing the magnet's poles also reverses the direction of force.
• The force is greatest when the current direction is perpendicular (90°) to the magnetic field.

Fleming's Left-Hand Rule

Stretch the thumb, forefinger and middle finger of your left hand so that they are mutually perpendicular to one another.

Finger	Indicates
Forefinger	Direction of magnetic field
Middle finger	Direction of electric current
Thumb	Direction of motion or force on the conductor

Memory tip: Forefinger = Field; Middle finger = Current; Thumb = Thrust (force/motion).

8. Medical Applications of Magnetism

• The heart and brain in the human body produce magnetic fields.
• MRI (Magnetic Resonance Imaging): Images of internal organs can be obtained using strong magnetic fields and radio waves through MRI technology.

9. Domestic Electric Circuits

In domestic wiring, electrical energy is delivered using three main types of insulated wires.

Wire	Insulation colour in the supplied notes	Function / potential
Live wire	Red	High potential (220 V in India)
Neutral wire	Black	Low potential (0 V); completes the circuit
Earth wire	Green	Safety grounding for metallic appliances

Potential difference in India (as stated in these notes): 220 V between the live wire and neutral wire.

Domestic distribution path

Electricity supply pole→Main supply→Electric fuse→Electricity meter→Distribution box→Separate circuits

Key safety concepts and hazards

Earth wire safety

The earth wire protects users from electric shocks in case of current leakage, especially in appliances with metallic bodies. It provides a low-resistance conducting path to the earth for leaked current.

Short circuit

A short circuit occurs when a live wire comes into direct contact with a neutral wire accidentally. The circuit resistance drops drastically, causing a dangerously large electric current to flow.

Overloading

Overloading occurs when the current drawn exceeds the rated current-carrying capacity of the conductor.

Causes of overloading

1. An accidental increase or surge in the voltage supply.
2. Connecting more than one high-power appliance to a single electrical socket.

Safety devices

Device	Function
Electric fuse	A safety device that melts and breaks the circuit during excessive current flow.
Earth wire	Provides grounding protection against current leakage.
MCB (Miniature Circuit Breaker)	An automatic switch that trips to interrupt current flow when an overload or short circuit is detected.

Safety reminder: Never experiment with household mains electricity. Practical electrical work should be done only under the supervision of a qualified person.

10. Quick Revision

Topic	Key point to remember
Magnetic poles	Like poles repel; unlike poles attract.
Oersted	Showed that electric current produces a magnetic field.
Bar magnet field	Outside N → S; inside S → N.
Straight conductor	Concentric circular magnetic field lines.
Right-Hand Thumb Rule	Thumb: current; curled fingers: magnetic field.
Circular coil	Field increases with current and number of turns; decreases with radius.
Solenoid	Many circular turns; uniform field inside; can form an electromagnet with soft iron.
Fleming's Left-Hand Rule	Forefinger: field; middle finger: current; thumb: force/motion.
MRI	Uses strong magnetic fields and radio waves.
Short circuit	Live and neutral wires make direct contact.
Overloading	Current exceeds the conductor's rated capacity.
MCB	Trips to interrupt current during overload or short circuit.

11. Self-Test: Multiple-Choice Questions

Choose an answer and select Check answers to see your score.

1. Who first demonstrated that electric current produces a magnetic field?

André-Marie Ampère H. C. Oersted Michael Faraday

2. Outside a bar magnet, magnetic field lines travel from:

South to North East to West North to South

3. Which rule gives the direction of the magnetic field around a straight current-carrying conductor?

Right-Hand Thumb Rule Fleming's Left-Hand Rule Law of reflection

4. Which part of Fleming's Left-Hand Rule indicates the direction of force?

Forefinger Middle finger Thumb

5. Which device automatically trips during an overload or short circuit?

MCB Compass Solenoid

MG SCHOOL SCIENCE
Class 10 Science • Magnetic Effects of Electric Current
Study notes arranged from the supplied chapter PDF.

Electricity Notes

MG SCHOOL SCIENCE • CLASS 10

Electricity

Chapter 11 • Complete Study Notes, Important Formulae, Activities and Solved Numericals

Class 10 ScienceChapter NotesNumerical ProblemsQuick Revision

Introduction to Electricity

Electricity plays a crucial role in our modern world, powering everything from homes and schools to hospitals and industries. In this chapter, we explore electric circuits, the factors that influence the flow of current, the heating effect of electric current and its practical applications.

Historical origin: The word electricity originates from the Greek word “Elektron” (amber). The Greek philosopher Thales was the first to observe the attracting capacity of certain materials when rubbed together.

📚 Chapter contents

1. Electric Current and Circuit 2. Electric Potential and Potential Difference 3. Circuit Diagram 4. Ohm’s Law 5. Factors Affecting Resistance 6. Resistors: Series and Parallel 7. Heating Effect of Electric Current 8. Electric Power Quick Formula Revision

1. Electric Current and Circuit

• Electricity is one of the most convenient and widely used forms of energy in the world.
• Conductors: Substances in which electric charge can flow freely. Metals are conductors. Copper and aluminium are commonly used in electricity.
• Insulators: Materials in which electric charges do not move freely. Rubber, glass and plastic are examples.
• Current electricity: Deals with moving charges.
• Electric circuit: A continuous and closed path of an electric current.

Electric current: The rate of flow of electric charge through a cross-section of a conductor.

I = Q / t

Here, I = electric current, Q = charge flown and t = time.

Flow of Electric Current and Units

• The SI unit of electric current is ampere (A).
• One ampere is the flow of one coulomb of charge per second: 1 A = 1 C s⁻¹.
• The unit is named after the French scientist André-Marie Ampère.
• Conventional current is taken opposite to the direction of flow of negatively charged electrons. It is along the direction in which positive charges would move.
• In conductors, electric current is due to the flow of electrons. The flow of 6.25 × 10¹⁸ electrons per second across a cross-section constitutes a current of 1 ampere.

📌 Solved Example 1: Charge Calculation

Question: A current of 0.75 A flows through a heater for 8 minutes. Calculate the amount of electric charge that passes through the circuit.

Given: I = 0.75 A; t = 8 min = 480 s

Formula: Q = I × t

Calculation: Q = 0.75 × 480 = 360 C

Result: The electric charge is 360 C.

2. Electric Potential and Potential Difference

The flow of electric charge in a circuit is similar to water flow in a pipe:

• The water pipe is analogous to the electric conductor, and the amount of water flowing across a section per second corresponds to electric current.
• Just as water flows from higher pressure (level) to lower pressure (level), electric current flows from higher electric potential to lower electric potential.
• The potential difference across a conductor is maintained by using a cell or battery.
• The chemical action within a cell generates the potential difference between its electrodes, due to which current flows through the circuit.

Potential difference: The work done to move a unit positive charge from one point to another in an electric circuit carrying current.

V_A − V_B = W / Q

SI unit: volt (V), where 1 V = 1 J / 1 C = 1 J C⁻¹.

📌 Solved Example 2: Work Done Calculation

Question: How much work is done in moving a charge of 3 C between two points with a potential difference of 9 V?

Given: Q = 3 C; V = 9 V

Formula: W = V × Q

Calculation: W = 9 × 3 = 27 J

Result: 27 J of work is done in moving the charge.

3. Circuit Diagram

A circuit diagram is a simplified representation of the components of an electrical circuit using either images of distinct parts or standard symbols.

• It shows the relative positions of all the elements and their connections to one another.
• It is often used to provide a visual representation of the circuit to an electrician or engineer.

4. Ohm’s Law

Georg Simon Ohm established a relationship between the electric current flowing through a conductor and the potential difference across its ends.

Statement: According to Ohm’s law, temperature remaining constant, the current passing through a conductor is directly proportional to the potential difference across its ends.

V ∝ I   ⇒   V = I × R   or   R = V / I

• The constant R is known as the resistance of the given conductor.
• For a given conductor, its resistance is constant at a given temperature.
• Electrical resistance is a measure of the opposition offered by a conductor to the flow of electric charge through it.
• The SI unit of electrical resistance is ohm (Ω), where 1 Ω = 1 V / 1 A.

Activity: Verifying Ohm’s Law

• Objective: To study the relationship between potential difference (V) across a nichrome wire and current (I) passing through it by varying the number of cells.
• Materials: Nichrome wire (0.5 m), ammeter, voltmeter, four 1.5 V cells, connecting wires, switch and circuit board.
• Procedure: Connect the nichrome wire in series with an ammeter and in parallel with a voltmeter using one 1.5 V cell. Record current and potential difference. Increase the cells to 2, 3 and 4 successively, recording I and V each time. Plot V against I.
• Conclusion: The ratio V/I remains constant in each case. The V-I graph is a straight line passing through the origin, proving V ∝ I.

Important note: Current through a resistor is inversely proportional to its resistance. If resistance is doubled, current gets halved, when the potential difference is unchanged.

5. Factors Affecting Resistance of a Conductor

At a given temperature, the resistance of a conductor depends on:

• Length (L): R ∝ L
• Area of cross-section (A): R ∝ 1/A
• Nature of the material of the conductor.

R = ρ × (L / A)

Here, ρ (rho) is the resistivity of the material.

• Resistivity is the resistance offered by a cube of that material of side 1 m when current flows perpendicular to opposite faces.
• Unit of resistivity: ohm-metre (Ω·m).
• Its value depends only on the nature of the material and temperature, and is independent of dimensions.
• Metals and alloys have low resistivity (10⁻⁸ to 10⁻⁶ Ω·m) and are good conductors. Insulators such as rubber and glass have resistivity of 10¹² to 10¹⁷ Ω·m.
• Pure metals have very low resistivity. Copper and aluminium are used for transmission lines.
• Alloys have higher resistivity and do not oxidise easily. Nichrome is used in heaters, irons and geysers.
• Tungsten is used for lamp filaments due to its high melting point.

Rheostat

A variable resistance device used to regulate current without changing the voltage source.

Ammeter

An instrument connected in series to measure current.

Voltmeter

An instrument connected in parallel to measure potential difference.

📌 Solved Example 3: Resistivity Calculation

Question: The resistance of a metal wire of length 1.5 m is 30 Ω at 25°C. If its diameter is 0.4 mm, find resistivity at 25°C.

Given: R = 30 Ω; d = 0.4 mm = 4 × 10⁻⁴ m; l = 1.5 m

Formula: ρ = R × A / l = R × (πd²/4) / l

Calculation: ρ = (30 × 3.1416 × (4 × 10⁻⁴)²) / (4 × 1.5) = 2.51 × 10⁻⁶ Ω·m

Result: Resistivity of the metal at 25°C is 2.51 × 10⁻⁶ Ω·m.

📌 Solved Example 4: Resized Wire Resistance

Question: A wire of length l and cross-sectional area A has resistance 6 Ω. What is the resistance of another wire of the same material with length l/3 and cross-sectional area 3A?

For wire 1: R₁ = ρ(l/A) = 6 Ω

For wire 2: R₂ = ρ((l/3)/(3A)) = ρ(l/9A) = (1/9) × R₁

R₂ = (1/9) × 6 Ω = 0.67 Ω (approximately).

Result: The new wire has resistance 0.67 Ω (approximately; the source notes also give a simplified rounded value of 1 Ω).

6. Resistance of System of Resistors

Resistors in an electric circuit can be connected in series or parallel arrangement.

Series Combination

• Current flowing through all resistors is the same.
• Total voltage equals the sum of voltage drops: V = V₁ + V₂ + V₃.
• Total equivalent resistance:

R_s = R₁ + R₂ + R₃ + ...

Parallel Combination

• Voltage across each resistor is the same and equals the total applied voltage.
• Current divides among resistors inversely proportional to resistance. I = I₁ + I₂ + I₃.
• Reciprocal of equivalent resistance:

1/R_p = 1/R₁ + 1/R₂ + 1/R₃ + ...

For two resistors:

R_p = (R₁ × R₂) / (R₁ + R₂)

Why Parallel Connection is Preferred in Household Circuits

• In series, if one component fails, the circuit breaks and all components stop working.
• In series, the same current flows through all appliances regardless of their requirement.
• Parallel circuits divide current so each appliance draws the required current with separate switches, and total circuit resistance decreases.

📌 Solved Example 5: Series Circuit and Power Analysis

Question: An electric lamp of resistance 20 Ω and a conductor of 4 Ω are connected in series to a 6 V battery. Calculate (a) total resistance, (b) circuit current, (c) potential difference across the lamp and conductor, and (d) power of the lamp.

Given: R₁ = 20 Ω; R₂ = 4 Ω; V = 6 V

1. Total resistance: R = R₁ + R₂ = 20 + 4 = 24 Ω.
2. Current: I = V/R = 6/24 = 0.25 A.
3. Voltage across lamp: V₁ = I × R₁ = 0.25 × 20 = 5 V.
4. Voltage across conductor: V₂ = I × R₂ = 0.25 × 4 = 1 V.
5. Power of lamp: P = V₁ × I = 5 × 0.25 = 1.25 W.

Results: Total resistance = 24 Ω; current = 0.25 A; voltage drops = 5 V and 1 V; lamp power = 1.25 W.

7. Heating Effect of Electric Current

According to Joule’s law of heating, when current I flows through resistance R for time t under voltage V, the electrical energy consumed or heat produced is:

H = W = Q × V = V × I × t = I² × R × t = (V² × t) / R

Unit: Joule (J).

• Formula H = I²Rt is preferred for series circuits (constant current I).
• Formula H = (V²t)/R is preferred for parallel circuits (constant voltage V).

📌 Solved Example 6: Electric Heater Power and Resistance

Question: An electric heater uses 900 W at maximum heat and 400 W at minimum heat, operating at 240 V. Calculate current and resistance in each case.

Formulae: I = P/V and R = V/I

(a) Maximum heating: P = 900 W, V = 240 V

• Current I = 900/240 = 3.75 A
• Resistance R = 240/3.75 = 64 Ω

(b) Minimum heating: P = 400 W, V = 240 V

• Current I = 400/240 = 1.67 A
• Resistance R = 240/1.67 ≈ 144 Ω

Result: Maximum heat → 3.75 A, 64 Ω. Minimum heat → 1.67 A, 144 Ω.

Practical Applications of Heating Effect

• Electric lighting – Electric bulb: The filament is made of high melting-point tungsten. It is filled with inert nitrogen and argon gas to prolong filament life.
• Electric fuse: A safety device placed in series. It consists of a wire with an appropriate low melting point. Excess current heats the wire beyond its melting point, breaking the circuit.

8. Electric Power

Definition: Electric power is defined as the time rate of doing electrical work.

P = W/t = V × I = I² × R = V² / R

• SI unit: Watt (W), where 1 watt = 1 volt × 1 ampere = 1 VA.
• Commercial unit of electrical energy: Kilowatt-hour (kWh).
• Conversion: 1 kWh = 1000 W × 3600 s = 3.6 × 10⁶ J.

⚡ Quick Formula Revision

Quantity / Concept	Formula	SI Unit
Electric current	I = Q/t	Ampere (A)
Electric charge	Q = I × t	Coulomb (C)
Potential difference	V = W/Q	Volt (V)
Ohm’s law	V = I × R	—
Resistance	R = V/I	Ohm (Ω)
Resistivity relation	R = ρL/A	Ω·m for ρ
Series resistance	Rs = R₁ + R₂ + ...	Ohm (Ω)
Parallel resistance	1/Rp = 1/R₁ + 1/R₂ + ...	Ohm (Ω)
Heat produced	H = I²Rt	Joule (J)
Electric power	P = VI = I²R = V²/R	Watt (W)
Electrical energy	E = P × t	Joule (J) or kWh

Study tip: Before solving a numerical, write the given quantities, convert all values into SI units, select the correct formula, substitute the values and include the final unit.

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Class 10 Science | Electricity – Chapter Notes

Our Environment Notes

 

MG SCHOOL SCIENCE • CLASS 10

Our Environment

Chapter 13 – Complete chapter notes, key concepts, comparison tables and quick revision.

Class 10 Science Chapter 13 Study Notes

📘 Chapter contents

1. Introduction 2. Ecosystem 3. Food Chains & Food Webs 4. Energy Flow 5. Human Activities 6. Garbage Management 7. Quick Summary

1. Introduction

Our environment is a complex and dynamic system that supports all living beings. It consists of physical, chemical and biotic factors that interact continuously to maintain life and ecological balance.

Physical factors

Natural elements such as landforms, climate, temperature, rainfall, wind and soil.

Chemical factors

Substances and chemical conditions present in air, water and soil, along with their interactions.

Biotic factors

Living organisms, including plants, animals and microorganisms, and their interactions within ecosystems.

Core concept: The environment functions through continuous interactions among physical, chemical and biotic components to sustain ecological balance.

2. Ecosystem: What Are Its Components?

An ecosystem is a functional unit formed by the interaction of living organisms, called biotic components, with the non-living physical and chemical environment, called abiotic components. Organisms influence the environment and are, in turn, affected by it.

Types of ecosystems

Natural ecosystems

Ecosystems that exist and function without deliberate human intervention.

Examples: Forests, lakes, rivers, oceans and grasslands.

Artificial or man-made ecosystems

Ecosystems created and maintained by humans.

Examples: Crop fields, aquariums, gardens and parks.

Components of an ecosystem

• Abiotic components: Non-living physical and chemical factors such as light, temperature, water, air, soil and minerals. Climate, soil-related conditions and topographic features are important abiotic factors.
• Biotic components: Living organisms such as producers, consumers and decomposers.

Producers, consumers and decomposers

• Producers or autotrophs: Green plants, algae and some cyanobacteria synthesise organic food from carbon dioxide and water using sunlight. This process is called photosynthesis. Producers form the base of food chains.
• Consumers or heterotrophs: Organisms that cannot prepare their own food and obtain it by feeding on producers or other consumers.
• Decomposers: Organisms such as bacteria and fungi that break down dead plants, dead animals and wastes into simpler substances. They return nutrients to the soil and make them available again to producers.

Division of consumers

• Herbivores: Consumers that feed on plants. Examples: goats and deer.
• Carnivores: Consumers that feed on other animals. Examples: tigers and crocodiles.
• Omnivores: Consumers that eat both plants and animals. Example: humans.
• Parasites: Organisms that live on or inside another organism, called the host, and obtain nutrients from it. Lice are animal parasites. Cuscuta (dodder) is a parasitic plant.

Decomposers help in nutrient recycling and maintain the fertility of the soil.

Classification of ecosystem components

Category	Role / Definition	Examples
Producers (Autotrophs)	Synthesise organic food using sunlight (photosynthesis).	Green plants, algae, cyanobacteria.
Consumers: Herbivores	Feed directly on plants (primary consumers).	Goats, deer.
Consumers: Carnivores and Omnivores	Feed on animals (carnivores) or both plants and animals (omnivores).	Tigers, crocodiles (carnivores); humans (omnivores).
Decomposers	Break down dead organic matter and recycle nutrients into soil.	Bacteria, fungi.

3. Food Chains and Food Webs

A food chain is a linear sequence of organisms through which food, energy and nutrients pass when one organism eats another.

Grass
Producer➜Deer
Herbivore➜Lion
Carnivore

Trophic levels in a food chain

Trophic levels are the successive feeding levels in a food chain. At each consumer level, organisms obtain food and energy from the level below them.

1. First trophic level: Producers or autotrophs, such as green plants, capture solar energy and convert it into chemical energy stored in food.
2. Second trophic level: Primary consumers or herbivores, such as deer, feed on producers.
3. Third trophic level: Secondary consumers or small carnivores, such as foxes, feed on herbivores.
4. Fourth trophic level: Tertiary consumers or larger carnivores feed on secondary consumers.

Key energy principles in food chains

• Base support: Energy captured by producers supports all the higher trophic levels.
• Solar energy conversion: Autotrophs convert solar energy into chemical energy stored in organic molecules. This energy is transferred to consumers and is also made available to decomposers through dead organisms and wastes.
• Energy loss as heat: At every transfer from one trophic level to the next, a considerable portion of energy is lost to the environment, mainly as heat during respiration and other metabolic activities.
• 1% solar capture rule: Green plants typically capture and convert about 1% of the sunlight falling on their leaves into chemical energy stored in food.
• 10% energy flow rule: Only about 10% of the energy or organic matter at one trophic level is generally converted into biomass at the next higher trophic level.
• Trophic level limitation: Because usable energy decreases progressively, food chains usually have only three or four major trophic levels.

Remember the 10% rule: Approximately 10% of the energy at any given trophic level is transferred to the next higher level. The remaining energy is lost as heat or used in metabolic processes.

Food web

Food chains in a natural ecosystem are interconnected because most organisms feed on more than one kind of organism. The network of these interconnected food chains is called a food web. Food webs show the complexity of feeding relationships and the movement of energy and materials within an ecosystem.

4. Energy Flow in Ecosystems

Energy flow in an ecosystem has two important characteristics: it is unidirectional and the amount of available energy progressively decreases at successive trophic levels.

1. Unidirectional flow

• One-way movement: Energy flows in one direction: from the Sun to producers and then to consumers. Decomposers obtain energy from dead organisms and wastes at all trophic levels.
• Non-reversible energy: Energy captured by producers does not return to the Sun. Energy lost as heat cannot be reused by earlier trophic levels.

2. Progressive diminishment

• Metabolic energy loss: Usable energy decreases at each trophic level because energy is lost as heat during respiration and other life processes and also leaves the body as waste.
• Constraint on food chain length: These energy losses limit the number of trophic levels in a food chain.

Biological magnification

Harmful chemicals used in agriculture, such as certain pesticides, enter the food chain. They are absorbed by plants and accumulate in the bodies of organisms that feed on those plants. The concentration of these non-biodegradable chemicals increases at each trophic level. This is called biological magnification. Their concentration is highest in top consumers, including humans.

Environmental hazard: Biological magnification leads to the maximum accumulation of non-biodegradable toxic chemicals, such as pesticides, in top carnivores and humans at the highest trophic level.

5. How Do Our Activities Affect the Environment?

Human activities such as deforestation, industrial production, the use of synthetic chemicals, improper waste disposal and over-exploitation of natural resources change the composition, structure and functioning of ecosystems. These changes can lead to pollution, loss of biodiversity, soil degradation and climate change.

Ozone layer and how it is getting depleted

• Stratospheric shield: The ozone layer is a region of the stratosphere containing a relatively high concentration of ozone (O₃). It absorbs most of the Sun's harmful ultraviolet (UV) radiation. This protective shield reduces UV-related damage such as skin cancer, cataracts and reduced plant productivity.
• Ozone vs molecular oxygen: Ozone is a molecule containing three oxygen atoms (O₃). Molecular oxygen (O₂) is essential for aerobic life.
• Beneficial vs harmful ozone: Ozone at ground level in the troposphere is a pollutant and can harm human health and vegetation. Ozone in the stratosphere is beneficial because it absorbs UV radiation.

Formation and breakdown of ozone

Ultraviolet radiation splits molecular oxygen into free oxygen atoms, which combine with molecular oxygen to form ozone:

O₂ ──(UV light)──➜ O + O
O₂ + O ──➜ O₃ (Ozone)

Ozone can also be broken down by natural and human-made processes. Synthetic chemicals, especially chlorofluorocarbons (CFCs), release chlorine in the stratosphere and catalyse the destruction of ozone.

Ozone depletion and international response

• Decline in ozone levels: From the late 1970s and into the 1980s, observations showed a significant decline in stratospheric ozone levels.
• Role of CFCs: The decline was linked to CFCs and other ozone-depleting substances widely used in refrigerants, aerosols and foam-blowing agents.
• The Montreal Protocol (1987): An international agreement adopted in 1987 to address this problem. It sought to freeze and then reduce the production and use of CFCs and related chemicals.
• Global impact: As a result of the Montreal Protocol and its subsequent amendments, the production of many CFCs has been phased out and safer alternatives have been introduced.

6. Managing the Garbage We Produce

Modern lifestyles and increased consumption generate large quantities of waste. Effective waste management reduces environmental harm, conserves resources and protects human health.

• Enzyme specificity: The enzymes of decomposers cannot break down many synthetic materials, such as most plastics. These materials therefore remain in the environment for a long time.
• Persistence of synthetic materials: Many man-made materials, especially plastics, resist decomposition and persist in the environment for decades or centuries. They can pollute land and water and create hazards for wildlife and humans.

Types of materials in garbage

Biodegradable wastes

Wastes that can be decomposed by microorganisms.

Examples: Fruit and vegetable peels, paper, cotton, jute, dung and food scraps.

Non-biodegradable wastes

Wastes that cannot be decomposed by microorganisms.

Examples: Plastics, polythene, metals, synthetic fibres, certain pesticides and radioactive wastes.

Principles and methods of waste management

1. Reduce

Minimise the generation of waste at its source. Avoid unnecessary disposable products and excessive packaging.

2. Reuse

Use articles more than once before discarding them. Refillable containers and repaired products are examples.

3. Recycle

Convert waste materials into raw materials for making new products. Paper, glass, metals and some plastics can be recycled.

4. Segregation

Separate biodegradable and non-biodegradable wastes at the source. This makes composting and recycling more efficient.

5. Composting

Decompose organic wastes biologically to produce compost, which can be used as a soil conditioner.

6. Sanitary landfills

Dispose of waste in engineered sites designed to isolate it from the surroundings and reduce pollution. Mainly used for non-recyclable wastes.

7. Controlled incineration

Burn waste under controlled conditions with suitable energy-recovery and pollution-control systems. It is appropriate only for certain types of waste and requires careful control of emissions.

Waste classification and disposal methods

Waste category	Characteristics and action of decomposers	Examples and effective disposal methods
Biodegradable wastes	Broken down into simple substances by microbial enzyme action; eco-friendly.	Peels, paper, cotton, dung and food scraps. Disposal: Composting, biogas generation.
Non-biodegradable wastes	Resist microbial decomposition; persist for decades or centuries.	Plastics, polythene, metals and pesticides. Disposal: Recycling, sanitary landfills, incineration.

7. What You Have Learned – Quick Revision

1. Ecosystem unity: An ecosystem comprises interacting biotic and abiotic components and functions as a unit.
2. Primary producers: Producers or autotrophs capture solar energy and form the base of food chains. Consumers and decomposers depend on them directly or indirectly.
3. Energy transfer efficiency: Green plants convert about 1% of sunlight into chemical energy, and only about 10% of the energy at one trophic level becomes available as biomass at the next level.
4. Food webs: Food chains are interconnected into food webs, which show the complexity of feeding relationships in ecosystems.
5. Human impacts: Human activities affect the environment through pollution, resource depletion, habitat destruction and other changes to ecosystems.
6. Ozone protection: Chemicals such as CFCs have damaged the stratospheric ozone layer. International action, including the Montreal Protocol, has been taken to reduce the use of these substances.
7. Waste management: Waste can be biodegradable or non-biodegradable. Reduction, reuse, recycling, segregation, composting and sanitary disposal are essential for protecting the environment.
8. Sustainability: Understanding ecosystems and human impacts helps us design conservation and sustainable-use measures that maintain ecological balance.

Chapter takeaway: Protecting the environment requires understanding ecosystem interactions, conserving resources, preventing pollution and managing waste responsibly.

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MG SCHOOL SCIENCE • Class 10 Science • Chapter 13: Our Environment

Heredity Notes

 

MG SCHOOL SCIENCE • CLASS 10

Heredity and Evolution

Structured chapter notes on variation, inheritance, Mendel’s experiments, genes, and sex determination.

Class 10 ScienceChapter NotesResponsive Study Page

📚 Chapter contents

Introduction 1. Variation 2. Heredity Mendel’s experiments Monohybrid cross Dihybrid cross 3. Genes and traits 4. Sex determination Quick revision Practice quiz

When living things reproduce, they produce new individuals that resemble their parents but are not exact copies. Asexual reproduction generally produces fewer differences, while sexual reproduction produces greater variation. This chapter explains how differences arise and how traits pass from one generation to the next.

1. Accumulation of Variation During Reproduction

• Basic body plan is inherited: Offspring inherit a basic design or body plan from their parents, so many core features remain similar across generations.
• Small changes each generation: Every generation may acquire small changes. Over many generations, these changes can accumulate.
• Inheritance across generations: Offspring carry inherited traits into the next generation.
• New variations continually arise: New differences appear through processes such as mutation and recombination.

Example: In asexual reproduction such as bacterial binary fission, daughter cells are nearly identical to the parent. Occasional DNA-copying errors can create small differences.

Remember: Sexual reproduction mixes genetic material from two parents. Independent assortment and recombination typically produce greater diversity.

Survival likelihood of variations

• Different variations have different chances of surviving and reproducing in a given environment.
• Survival and reproductive success depend on traits and environmental conditions.
• Heat-resistant bacteria are more likely to survive during a heat wave than heat-sensitive bacteria.
• Environmental selection of favourable traits is a core mechanism of evolution.

2. What is Heredity?

Heredity is the process by which parents pass characteristics to their offspring through reproduction. It explains the transmission of traits such as skin colour, hair type, eye colour and height from one generation to the next.

Inherited and acquired traits

Inherited traitsFeatures passed from parents to offspring through genes; examples include eye colour and blood group.

Acquired traitsChanges in the body or behaviour that develop during an organism’s life, such as a scar or language skills. They are generally not transmitted genetically to offspring.

• Genetic variation: Offspring inherit genes in different combinations, producing variation in traits.
• Illustration: If parents carry different eye-colour genes, a child may inherit different combinations depending on which genes are passed on.
• Earlobe example: Free and attached earlobes are used as an example of inherited variation.

Mendel’s Contributions – Rules for Inheritance of Traits

Gregor Johann Mendel, known as the Father of Genetics, established fundamental rules of inheritance through experiments with pea plants.

Mendel selected plants with contrasting traits such as round or wrinkled seeds and tall or short stems. He initially crossed plants differing in one trait at a time.

(a) Monohybrid Cross – Single Trait Inheritance

A monohybrid cross follows the inheritance of one pair of contrasting traits. Mendel crossed a homozygous tall plant (TT) with a homozygous short plant (tt).

F1 generationTT × tt produces all Tt offspring. All are tall, showing that tallness (T) is dominant.

F2 generationWhen F1 plants (Tt) self-pollinate, both tall and short plants appear, approximately three tall for every one short.

F2 cross: Tt × Tt

×

T

t

T

TT

Tt

t

Tt

tt

Genotype: 1 : 2 : 1Phenotype: 3 : 1

Genotypic ratio: 1 TT : 2 Tt : 1 tt.

Phenotypic ratio: 3 tall : 1 short, because TT and Tt are tall while tt is short.

Generation	Genotype ratio	Phenotype ratio
F1	100% Tt (heterozygous)	100% tall
F2	1 TT : 2 Tt : 1 tt (1:2:1)	3 tall : 1 short (3:1)

Mendel’s conclusion: Each trait is controlled by two factors (now called alleles), one inherited from each parent. The alleles segregate during formation of reproductive cells, so each gamete carries one allele for each trait.

(b) Dihybrid Cross – Two Trait Inheritance

A dihybrid cross follows two characteristics at the same time: seed shape and seed colour. Round (R) and yellow (Y) are dominant over wrinkled (r) and green (y).

• Parental cross: RRYY (round yellow) × rryy (wrinkled green).
• F1 generation: All offspring are RrYy, with round yellow seeds.
• F2 generation: Self-pollination of RrYy plants produces four phenotype combinations in the ratio 9:3:3:1.

F2 phenotype	Ratio
Round yellow	9
Round green	3
Wrinkled yellow	3
Wrinkled green	1

Principle of independent assortment: Alleles of different genes segregate independently during gamete formation. This is the basis of dihybrid inheritance.

3. How Do Genes Produce Traits?

• DNA and genes: DNA is present in every cell and contains instructions for making proteins. A segment of DNA that contains instructions for a specific protein is called a gene.
• Proteins determine traits: Proteins, including enzymes and structural proteins, carry out functions that lead to observable traits. For example, plant height may depend on a hormone whose production requires an enzyme.
• Two copies of each gene: Most body cells have two copies of each gene, one from each parent. Gametes (sperm and egg) have only one copy.
• Alleles: Different forms of a gene are called alleles.
• Homozygous: Both copies of a gene are identical.
• Heterozygous: The two copies of a gene are different.
• Dominant and recessive: In many cases, a dominant allele masks the effect of a recessive allele in a heterozygous condition.
• Contribution from parents: Each parent contributes one allele for every gene, so both contribute equally to the offspring’s genotype.
• Role of gametes: Gametes carry a single set of alleles. Their fusion restores the pair of alleles.
• Environmental effects: The environment can influence gene expression and phenotype. Nutrition affects height in humans, while temperature can affect fur colour in some animals.

Traits are determined by proteins produced from genes. These inheritance principles apply to most sexually reproducing organisms. In asexual reproduction, variation arises mainly from mutations and copying errors.

4. Sex Determination

Sex-determination mechanisms vary among organisms.

• Temperature-dependent sex determination: In some reptiles, such as many turtles and crocodiles, the temperature at which eggs develop determines the sex of hatchlings.
• Environmental sex change: Some animals, such as certain snails and fish, can change sex in response to environmental or social conditions.

Sex determination in humans

• Humans have 23 pairs of chromosomes in each somatic (body) cell.
• 22 pairs are autosomes, which carry many genes for body traits.
• The 23rd pair are sex chromosomes, which determine genetic sex.
• Female (XX): Females have two X chromosomes. Each egg carries one X chromosome.
• Male (XY): Males have one X and one Y chromosome. Sperm carry either an X or a Y chromosome.
• The mother contributes an X chromosome. The father contributes either X or Y.

Chromosome contribution	Combination	Genetic sex
Mother X + Father X	XX	Female (girl)
Mother X + Father Y	XY	Male (boy)

Key point: The mother always contributes an X chromosome. The father’s sperm contributes either X or Y, determining whether the combination is XX or XY.

Quick Revision – Important Terms

Heredity

Passing characteristics from parents to offspring through reproduction.

Variation

Differences among individuals of the same species; variation can arise through mutation and genetic recombination.

Gene and allele

A gene is a segment of DNA carrying instructions for a specific protein. Different forms of a gene are called alleles.

Dominant and recessive

A dominant allele can mask the effect of a recessive allele in a heterozygous condition.

Homozygous and heterozygous

Homozygous means two identical alleles; heterozygous means two different alleles.

Monohybrid and dihybrid ratios

F2 monohybrid ratios: genotype 1:2:1 and phenotype 3:1. F2 dihybrid phenotype ratio: 9:3:3:1.

Human sex chromosomes

XX is the female chromosome combination and XY is the male chromosome combination.

Practice Quiz

Choose one answer for each question, then select Check answers.

1. Who is known as the Father of Genetics? Charles Darwin Gregor Johann Mendel Louis Pasteur

2. What is the F2 phenotypic ratio in a monohybrid cross? 1:2:1 9:3:3:1 3:1

3. A segment of DNA that contains instructions for a specific protein is a: Gene Tissue Chromosome pair

4. Which chromosome combination is XY? Female Male Both

5. What is the F2 phenotypic ratio in a dihybrid cross? 3:1 1:2:1 9:3:3:1

MG SCHOOL SCIENCE • Class 10 Science • Heredity and Evolution