Sunday, 8 November 2026

Temperature And it's Measurements

NCERT SOLUTIONS

🌡️ Temperature and Its Measurement

Class 6 Science | Chapter Study Material

Complete Textbook Questions & Answers

📘 Chapter Overview
Learn about temperature, thermometers, Celsius and Fahrenheit scales, laboratory thermometers and clinical thermometers through these NCERT textbook solutions.

📚 Quick Navigation

Let Us Enhance Our Learning
In-text Questions and Answers
Important Concepts
Quick Revision

📝 Let Us Enhance Our Learning

Question 1. The normal temperature of a healthy human being is close to _______.

(i) 98.6°C
(ii) 37.0°C
(iii) 32.0°C
(iv) 27.0°C

Answer: (ii) 37.0°C

Question 2. 37°C is the same temperature as _______.

(i) 97.4°F
(ii) 97.6°F
(iii) 98.4°F
(iv) 98.6°F

Answer: (iv) 98.6°F

Question 3. Fill in the blanks.

(i) The hotness or coldness of a system is determined by its _______.

Answer: Temperature.

(ii) The temperature of ice-cold water cannot be measured by a _______ thermometer.

Answer: Clinical thermometer.

(iii) The unit of temperature is degree _______.

Answer: Celsius.

Question 4. The range of a laboratory thermometer is usually _______.

(i) 10°C to 100°C
(ii) -10°C to 110°C
(iii) 32°C to 45°C
(iv) 35°C to 42°C

Answer: (ii) -10°C to 110°C

Question 5. Four students used a laboratory thermometer to measure the temperature of water. Who followed the correct way?

(i) Student 1
(ii) Student 2
(iii) Student 3
(iv) Student 4

Answer: (ii) Student 2

Explanation: Student 2 is measuring the temperature correctly because the thermometer bulb is fully immersed in the water and is not touching the sides or bottom of the container. This ensures it only measures the water's temperature.

Question 6. Colour to show the red column on the drawings of thermometers as per the temperatures written below.

Answer: This is a diagram activity. Colour the thermometer liquid column up to the specified temperature mark on each drawing.

Question 7. Observe the part of the thermometer shown and answer the following questions.

(i) What type of thermometer is it?

Answer: This is a laboratory thermometer, characterised by its long, narrow tube and a scale that typically ranges beyond the human body temperature range.

(ii) What is the reading of the thermometer?

Answer: 26°C.

(iii) What is the smallest value that this thermometer can measure?

Answer: -10°C.

Question 8. A laboratory thermometer is not used to measure our body temperature. Give a reason.

Answer: A laboratory thermometer is not used to measure human body temperature because:

It lacks a kink (constriction) to prevent the mercury/liquid from falling automatically.
It requires upright placement.
It is designed to measure broader temperature ranges.
It is inconvenient and potentially unsafe for body temperature measurement.

Question 9. Vaishnavi has not gone to school as she is ill. Her mother has kept a record of her body temperature for three days. Answer the following.

(i) What was Vaishnavi's highest recorded temperature?

Answer: 40.0°C.

(ii) On which day and at what time was her highest temperature recorded?

Answer: Day One at 7 pm.

(iii) On which day did Vaishnavi's temperature return to normal?

Answer: Day Three.

Question 10. If you have to measure the temperature 22.5°C, which of the following three thermometers will you use? Explain.

Answer: We will use thermometer (b).

The smallest division represents 1°C on thermometer (a) and 2°C on thermometer (c). Only thermometer (b) has divisions of 0.5°C, allowing 22.5°C to be read directly and accurately.

Question 11. The temperature shown by the thermometer is:

(i) 28.0°C
(ii) 27.5°C
(iii) 26.5°C
(iv) 25.3°C

Answer: (ii) 27.5°C

Question 12. A laboratory thermometer has 50 divisions between 0°C and 100°C. What does each division of this thermometer measure?

Answer: Each division measures 2°C.

Value of each division = Total temperature range ÷ Total divisions

= 100°C ÷ 50

= 2°C

Therefore, each division represents 2°C.

Question 13. Draw the scale of a thermometer in which the smallest division reads 0.5°C. You may draw only the portion between 10°C and 20°C.

Answer: Mark the main numbers at 10°C, 11°C, 12°C and so on up to 20°C. Add one subdivision mark between each degree to represent 0.5°C increments.

Temperature	Marking
10°C	10.0°C
10.5°C	10.5°C
11°C	11.0°C
11.5°C	11.5°C
12°C	12.0°C
...	...
20°C	20.0°C

Question 14. Someone tells you that she has a fever of 101 degrees. Does she mean it on the Celsius scale or Fahrenheit scale?

Answer: She means the temperature on the Fahrenheit scale (°F).

Human body temperature normally ranges between 35°C and 42°C (which corresponds to 95°F to 107.6°F). A body temperature of 101°C would be far above lethal limits.

📖 In-text Questions and Answers

Question 1. Can it always be correctly judged that a person has fever only by touching the person? (Page 123)

Answer: No. It cannot always be correctly judged that a person has a fever only by touch.

If a person has a normal body temperature and the hand touching them is cold, the person will feel warm.
If the hand touching the person is warm, a person with a fever may seem to have a normal temperature.
To accurately determine body temperature, a clinical thermometer must be used.

Question 2. Do small children generally have slightly higher body temperatures as compared to adults? (Page 128)

Answer: Yes. Small children usually have slightly higher body temperatures compared to adults.

This is because their metabolic bodies work harder to grow rapidly, generating more heat.

Children: 37.0°C to 37.5°C
Adults: 36.1°C to 37.2°C

Question 3. Do old people, even when healthy, generally have lower body temperatures than young adults? (Page 128)

Answer: Yes. Even healthy older adults generally have lower body temperatures than young adults.

As people age, metabolic processes slow down, producing less body heat. Normal body temperature for older adults is often around 36.2°C to 36.8°C.

Question 4. Can a clinical thermometer be used for measuring the temperature of boiling water? Or for measuring the temperature of ice? (Page 129)

Answer: No. A clinical thermometer cannot be used to measure the temperature of boiling water or ice.

A clinical thermometer is designed exclusively for human body temperature (35°C to 42°C).
Boiling water (100°C) far exceeds its scale and may break the glass tube.
Ice (0°C) is below its lower limit and cannot be measured accurately.
A laboratory thermometer should be used for measuring extreme temperatures like boiling water or ice.

⭐ Important Concepts

1. Temperature

Temperature determines the hotness or coldness of a system.

2. Normal Human Body Temperature

Approximately 37°C or 98.6°F.

3. Laboratory Thermometer

Usually has a range of -10°C to 110°C.

4. Smallest Division

The value represented by the smallest interval on a thermometer scale.

⚠️ Remember: A clinical thermometer is not suitable for measuring the temperature of ice or boiling water.

📊 Thermometer Comparison

Feature	Clinical Thermometer	Laboratory Thermometer
Purpose	Body temperature	Substances
Range in this chapter	35°C–42°C	-10°C–110°C
Kink	Has a kink	No kink
Use	Human body	Laboratory experiments

🚀 Quick Revision

Important facts to remember

Normal human body temperature = 37°C.
37°C = 98.6°F.
Temperature is measured using a thermometer.
Unit of temperature = degree Celsius.
Laboratory thermometer range = -10°C to 110°C.
22.5°C can be measured using a thermometer with 0.5°C divisions.
Each division in a thermometer with 50 divisions between 0°C and 100°C = 2°C.
101 degrees of fever refers to Fahrenheit.

❓ Frequently Asked Questions

What is the normal human body temperature?

The normal human body temperature is approximately 37°C or 98.6°F.

Why is a laboratory thermometer not used for body temperature?

It does not have a kink to prevent the liquid column from falling automatically and is not designed specifically for body temperature measurement.

What is the range of a laboratory thermometer?

The usual range given in this chapter is -10°C to 110°C.

Can a clinical thermometer measure boiling water?

No. Boiling water is approximately 100°C, which is beyond the clinical thermometer's range.

Saturday, 7 November 2026

Chemistry Passing Package | Class 10 Science

MG SCHOOL SCIENCE

CHEMISTRY PASSING PACKAGE

Class 10 Science | Important Repeated Concepts

Definitions • Chemical Equations • Important Reactions • Give Reasons

EXAM PREPARATION NOTES

01. Chemical Reactions and Equations

Key Definitions

Chemical Reaction Reactants are converted into products.

Chemical Equation Symbolic representation of a chemical reaction.

Balanced Chemical Equation Same number of atoms on LHS and RHS; follows the Law of Conservation of Mass.

Changes in Chemical Reactions: Change in colour, change in temperature, change in state and evolution of gas.

Important Balanced Chemical Equations

1. H₂ + Cl₂ → 2HCl

2. 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

3. 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂

4. CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

5. CH₄ + 2O₂ → CO₂ + 2H₂O

6. CaCO₃ → CaO + CO₂

7. Mg + 2HCl → MgCl₂ + H₂

8. Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

9. 3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃

10. Pb(s) + CuCl₂(aq) → PbCl₂(aq) + Cu(s)

11. 2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g)

12. Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

13. ZnCO₃(s) → ZnO(s) + CO₂(g)

14. 2AgCl → 2Ag + Cl₂

15. 2H₂ + O₂ → 2H₂O

16. Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

17. N₂ + 3H₂ → 2NH₃

18. NaCl + AgNO₃ → AgCl + NaNO₃

Types of Chemical Reactions

1. Combination Reaction

Two or more reactants combine to form a single product.

CaO + H₂O → Ca(OH)₂ + Heat

Quicklime to Slaked Lime

C + O₂ → CO₂

Burning of coal.

2H₂ + O₂ → 2H₂O(l)

Formation of water.

2. Decomposition Reaction

A single reactant breaks down into two or more products.

Thermal Decomposition

2FeSO₄ → Fe₂O₃ + SO₂ + SO₃

Crystals lose water when heated and change colour.

Cement Production

CaCO₃ → CaO + CO₂

Calcium oxide is used in the manufacture of cement.

Lead Nitrate Heating

2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂

Emission of brown fumes of nitrogen dioxide (NO₂).

Electrolytic Decomposition

2H₂O → 2H₂ + O₂

Cathode: H₂ | Anode: O₂

Photolytic Decomposition

2AgCl → 2Ag + Cl₂

White silver chloride turns grey in sunlight.

2AgBr → 2Ag + Br₂

Used in black and white photography.

3. Oxidation, Reduction and Redox Reactions

Oxidation: Addition of oxygen.

2Cu + O₂ → 2CuO

2Zn + O₂ → 2ZnO

Reduction: Removal of oxygen.

ZnO + C → Zn + CO

Redox Reaction: Oxidation and reduction occur simultaneously in the same reaction.

CuO + H₂ → Cu + H₂O

Oxidised and Reduced Reactants Summary

Chemical Reaction	Oxidised Substance	Reduced Substance
Na + O₂ → Na₂O	Na	O₂
CuO + H₂ → Cu + H₂O	H₂	CuO
ZnO + C → Zn + CO	C	ZnO

Displacement and Double Displacement Reactions

Displacement Reaction: More reactive element displaces a less reactive element.

Fe + CuSO₄ → FeSO₄ + Cu

Iron displaces copper from copper sulphate as iron is more reactive.

Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

Double Displacement Reaction: Exchange of ions between reactants.

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Precipitation Reaction: An insoluble substance (precipitate) is formed.

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Precipitate: BaSO₄

Ions involved: Ba²⁺ and SO₄²⁻

Energy Changes, Corrosion and Rancidity

Exothermic Reaction Heat is released.

CaO + H₂O → Ca(OH)₂ + Heat

CH₄ + 2O₂ → CO₂ + 2H₂O

Endothermic Reaction Heat is absorbed.

CaCO₃ → CaO + CO₂

Corrosion: Metal reacts with atmospheric substances to form undesirable compounds (e.g., rusting of iron).

Rancidity: Change in smell or taste of oil/fat-containing foods due to oxidation.

Prevention of Rancidity: Use antioxidants, refrigerate food, flush packaging with nitrogen gas and store in air-tight containers.

02. Acids, Bases and Salts

Properties of Acids and Bases

Property	Acids	Bases
Taste	Sour taste	Bitter taste
Ions Produced	Produce H⁺ ions in aqueous solution	Produce OH⁻ ions in aqueous solution
Litmus Test	Turns Blue litmus to Red	Turns Red litmus to Blue
pH Range	Below 7 (<7)	Above 7 (>7)
Examples	HCl, H₂SO₄, HNO₃	NaOH, KOH, Ca(OH)₂

Key Reactions of Acids and Bases

Reaction with Metals: Acid + Metal → Salt + Hydrogen gas

H₂SO₄ + Zn → ZnSO₄ + H₂

Reaction with Metal Carbonates: Acid + Metal Carbonate → Salt + Water + Carbon Dioxide

HCl + NaHCO₃ → NaCl + H₂O + CO₂

Reaction with Metal Oxides: Acid + Metal Oxide → Salt + Water

2HCl + ZnO → ZnCl₂ + H₂O

Neutralization Reaction: Acid + Base → Salt + Water

NaOH + HCl → NaCl + H₂O

Naturally Occurring Acids

Source	Naturally Occurring Acid
Vinegar	Acetic acid
Orange / Lemon	Citric acid
Tamarind	Tartaric acid
Tomato	Oxalic acid
Sour milk (Curd)	Lactic acid
Nettle sting / Ant sting	Methanoic acid

Important pH Values and Definitions

Blood pH7.2 to 7.8

Acid Rain pHBelow 5.6

Strong AcidCompletely dissociates in water.

Weak AcidIncompletely dissociates in water.

Concentrated Acid: High concentration of H⁺ ions OR larger amount of acid in less water.

Dilute Acid: Low concentration of H⁺ ions OR less amount of acid in larger volume of water.

Tooth Decay Causes and Prevention: Bacteria in mouth convert sugar into acid, causing tooth decay. Basic toothpaste neutralizes acid to prevent decay.

pH Classification of Salts

Salt Type	Combination	pH Level	Example
Neutral Salt	Strong Acid + Strong Base	pH = 7	NaCl
Acidic Salt	Strong Acid + Weak Base	pH < 7	NH₄Cl
Basic Salt	Weak Acid + Strong Base	pH > 7	Na₂CO₃

Chlor-Alkali Process and Industrial Chemicals

2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂

Brine SolutionAqueous solution of sodium chloride.

NaOH UsesSoaps, detergents and paper making.

Cl₂ UsesWater treatment, swimming pools and PVC manufacture.

H₂ UsesRocket fuel and margarine.

Important Chemical Compounds

Common Name	Chemical Name	Formula	Key Uses
Washing Soda	Sodium carbonate	Na₂CO₃	Manufacture of borax, softening hard water
Baking Soda	Sodium hydrogen carbonate	NaHCO₃	Antacid, ingredient in baking powder
Bleaching Powder	Calcium oxychloride	CaOCl₂	Bleaching clothes, oxidizing agent, disinfecting water
Plaster of Paris	Calcium sulphate Hemihydrate	CaSO₄·½H₂O	Plastering fractured bones, making toys and decorative items

Water of Crystallisation: Fixed number of water molecules present in one formula unit of a salt (e.g., CuSO₄·5H₂O has 5 water molecules).

Marble and Limestone Formula: Calcium carbonate (CaCO₃).

Soil Treatment: Farmers treat acidic soil with slaked lime (Ca(OH)₂) when soil acidity increases.

03. Metals and Non-Metals

Physical and Chemical Properties

Property	Metals	Non-Metals
Sonorous	Yes (produces ringing sound)	No
Ductility	Ductile (can be drawn into thin wire; Gold is most ductile)	Non-ductile
Malleability	Malleable (can be beaten into thin sheets)	Non-malleable
Lustre	Lustrous (shiny surface)	Non-lustrous
Electrical and Heat Conductivity	Good conductors of heat and electricity	Poor conductors
Reaction with Dilute Acids	Liberates H₂ gas from dilute acids	Does not liberate H₂ gas
Nature of Oxides	Basic in nature	Acidic in nature
Electrochemical Nature	Electropositive	Electronegative

Special Concepts and Ionic Compounds

Amphoteric Oxides: Metal oxides that react with both acids and bases to produce salt and water.

Examples: Al₂O₃, ZnO.

Ionic Compounds: Compounds formed by the transfer of electrons from a metal to a non-metal.

Formation of NaCl

Formation of MgCl₂

Properties of Ionic Compounds:

Hard and brittle.
High melting and boiling points due to strong inter-ionic electrostatic forces.
Soluble in water, insoluble in organic solvents.
Conduct electricity in molten/solution state, not in solid state due to fixed ions.

Extraction of Zinc

Roasting (Sulphide Ore): Heating sulphide ore strongly in presence of excess air.

2ZnS + 3O₂ → 2ZnO + 2SO₂

Calcination (Carbonate Ore): Heating carbonate ore strongly in presence of limited air.

ZnCO₃ → ZnO + CO₂

Reduction: Reducing metal oxide using carbon/coke.

ZnO + C → Zn + CO

Corrosion, Prevention and Alloys

Corrosion Definition: Attack on metals by atmospheric substances to form undesirable compounds.

Rusting of IronIron reacts with atmospheric substances.

CopperForms green coat of Copper Carbonate.

SilverTurns black due to Silver Sulphide.

Corrosion Prevention: Painting, oiling, greasing, galvanising, chrome plating, anodising and alloy formation.

Galvanising: Process of coating iron/steel with a thin layer of Zinc to prevent rusting.

Alloys Definition: Homogeneous mixture of two or more metals (or metal and non-metal).

Common Alloys

Alloy	Composition
Brass	Copper + Zinc
Bronze	Copper + Tin
Solder	Lead + Tin

Liquid Elements at Room Temperature: Mercury (Liquid metal), Bromine (Liquid non-metal).

Scientific Reasoning – Give Reasons Questions

Q1. Metals are used in making cooking vessels?

Answer: Metals are good conductors of heat, have high melting points, and possess high malleability.

Q2. Sodium metal is stored in kerosene?

Answer: Sodium reacts vigorously with atmospheric oxygen and moisture, but does not react with kerosene.

Q3. Calcium reaction with water does not catch fire?

Answer: The reaction of calcium with water is less violent; heat evolved is insufficient for hydrogen to catch fire.

Q4. Ionic compounds have high melting and boiling points?

Answer: They have strong electrostatic forces of attraction between oppositely charged ions requiring high energy to break.

Q5. H₂ gas is not liberated when metal reacts with concentrated HNO₃?

Answer: Concentrated HNO₃ is a strong oxidizing agent; it oxidizes the H₂ produced into water (H₂O).

Q6. ZnO and Al₂O₃ are called amphoteric oxides?

Answer: They react with both acids and bases to yield salt and water.

Q7. Gold is used to make jewellery?

Answer: Gold is lustrous, highly ductile, malleable, and extremely unreactive (least reactive metal).

Q8. Solid ionic compounds do not conduct electricity?

Answer: In solid state, ions are held in fixed positions and cannot move freely.

04. Carbon and Its Compounds

Bonding and Versatile Nature of Carbon

Covalent Bond Sharing of electrons between two atoms.

Ionic Bond Transfer of electrons from one atom to another.

Catenation Carbon's unique ability to form bonds with other carbon atoms, creating long chains or rings.

Tetravalency Carbon has 4 valence electrons and can bond with 4 other atoms.

Why C⁴⁺ cannot form: Removing 4 electrons requires a massive amount of energy.

Why C⁴⁻ cannot form: 6 protons in the nucleus cannot hold 10 electrons easily.

Classification of Hydrocarbons

Hydrocarbon Type	Bonding	General Formula	First Member	Flame Character
Alkanes (Saturated)	Single bond (C–C)	CₙH₂ₙ₊₂	Methane (CH₄)	Clean blue flame
Alkenes (Unsaturated)	Double bond (C=C)	CₙH₂ₙ	Ethene (C₂H₄)	Yellow smoky flame
Alkynes (Unsaturated)	Triple bond (C≡C)	CₙH₂ₙ₋₂	Ethyne (C₂H₂)	Yellow smoky flame

Functional Groups and Isomerism

Functional Group	Symbol
Alcohol	–OH
Aldehydes	–CHO
Ketone	C=O
Carboxylic Acid	–COOH

Structural Isomers: Compounds with the same molecular formula but different structural formulas.

Example: n-butane and isobutane.

Chemical Reactions of Carbon Compounds

Oxidation: Alcohols are oxidized to carboxylic acids using alkaline KMnO₄ or acidified K₂Cr₂O₇.

Addition Reaction / Hydrogenation: Hydrogen added to unsaturated hydrocarbons using Nickel (Ni) or Palladium catalyst to produce saturated fats.

Unsaturated oil + H₂ → Saturated fat

Substitution Reaction: Hydrogen atoms of a hydrocarbon are replaced by other atoms.

CH₄ + Cl₂ → CH₃Cl + HCl

Combustion Reaction: Burning carbon compounds in air to produce CO₂, heat and light.

2CH₃OH + 3O₂ → 4H₂O + 2CO₂

Important Carbon Compounds and Processes

Ethanol Uses and Reactions: Used in alcoholic drinks, tincture iodine and medicines. Concentrated H₂SO₄ acts as a dehydrating agent removing water from ethanol.

Ethanoic Acid (Glacial Acetic Acid): Pure ethanoic acid has a melting point of 290 K and freezes in winter, earning the name Glacial Acetic Acid.

Esterification: Reaction between carboxylic acid and alcohol to form pleasant-smelling esters (used in perfumes and flavouring agents).

Saponification: Reaction of alkaline base with long-chain carboxylic acid to form soap.

Soaps: Sodium salts of long-chain fatty acids; forms micelles with oil/dirt; does not lather in hard water.

Detergents: Sodium/Potassium salts of sulphonic acids; forms lather in both hard and soft water.

Formula and Molecular Structures Summary

Compound Name	Molecular Formula	Structural Notes
Cyclohexane	C₆H₁₂	Cyclic alkane ring with single bonds
Benzene	C₆H₆	Aromatic ring with alternating double bonds
Propyne	C₃H₄	Three-carbon alkyne with one triple bond
Butane	C₄H₁₀	Four-carbon alkane (straight and branched isomers)
Propanoic Acid	C₃H₆O₂	Three-carbon carboxylic acid (–COOH)
Pentane	C₅H₁₂	Five-carbon alkane

Electron Dot Structure Requirements

MethaneCH₄

EtheneC₂H₄

Oxygen MoleculeO₂

Hydrogen MoleculeH₂

Nitrogen MoleculeN₂

Important: Practise drawing the electron dot structures of all five molecules listed above.

EXAM PREPARATION TIP

Revise all important definitions, balanced chemical equations, chemical properties, tables, formulas and Give Reasons questions. Practise writing chemical equations and electron dot structures.

Physics Passing Package | Class 10 Science

MG SCHOOL SCIENCE PRESENTS

CLASS 10 PHYSICS
PASSING PACKAGE

Most Important Concepts • Definitions • SI Units • Formulas

SSLC EXAMINATION REVISION NOTES

1. ELECTRICITY

SI Units

Physical Quantity	Symbol	SI Unit
Electric Current	I	Ampere (A)
Electric Charge	Q	Coulomb (C)
Electric Power	P	Watt (W)
Potential Difference / Voltage	V	Volt (V)
Resistance	R	Ohm (Ω)
Resistivity	ρ	Ohm metre (Ω m)
Commercial Unit of Electricity	E	kWh

Electric Components and Measuring Instruments

Voltmeter: It measures the voltage. Connected in parallel.

Ammeter: It measures the current. Connected in series.

Definitions and Key Terms

Electric Current: Flow of electric charge through a conductor.
Formula: I = Q/t

Define 1 Ampere: 1 A = 1 C / 1 s

Potential Difference: Work done to move electric charge.
Formula: V = W/Q

Define 1 Volt: 1 V = 1 J / 1 C

Resistance: Opposition offered to the flow of current.

Define 1 Ohm: 1 Ω = 1 V / 1 A

Factors Affecting Resistance

Length (R ∝ l)
Thickness / Area of cross-section (R ∝ 1/A)
Materials
Temperature

Ohm's Law

At constant temperature, the potential difference across a conductor is directly proportional to the current flowing through it.
V ∝ I
V = IR

Series and Parallel Combination of Resistors

Series Combination	Parallel Combination
Resistance increases.	Resistance decreases.
Current is the same.	Current is divided.
Voltage is divided.	Voltage is the same.
If one device fails, the other does not work.	If one device fails, the other works properly.

Series ResistanceRs = R1 + R2 + R3

Parallel Resistance1/Rp = 1/R1 + 1/R2 + 1/R3

Joule's Law of Heating

Heat produced in a conductor is directly proportional to:

Square of current (I²)
Resistance (R)
Time (t)

H = I²Rt

Electric Power

Electric power is the rate at which electric energy is consumed in an electric circuit.
P = VI

Important Physics Formulas

Electric CurrentI = Q/t

Potential DifferenceV = W/Q

Ohm's LawV = IR

Series ResistanceRs = R1 + R2 + R3

Parallel Resistance1/Rp = 1/R1 + 1/R2 + 1/R3

Joule's HeatingH = I²Rt

Electric PowerP = VI

Electrical EnergyE = P × t

Electric Devices

Electric Bulb Filament: Tungsten, because of its high melting point and high resistance.
Electric Bulb Gas: Argon / Nitrogen, because they increase the life of the filament.
Electric Bulb Working: When current passes through the filament, it becomes hot and emits light.
Fuse: A safety device that protects the electric circuit. It is connected in series. If current is high, it becomes hot, melts and breaks the circuit.
Heating Devices: Electric toaster, electric oven, electric kettle, electric bulb and electric fuse.
Alloys: Nichrome is used in electrical heating devices because of its high melting point and high resistance.

⭐ Quick Revision – Electricity

SI unit of current – Ampere.
SI unit of charge – Coulomb.
SI unit of resistance – Ohm.
Voltmeter – Parallel connection.
Ammeter – Series connection.
Ohm's law – V = IR.
Joule's law – H = I²Rt.
Commercial unit – kWh.

2. MAGNETIC EFFECTS OF ELECTRIC CURRENT

Magnetic Field and Its Properties

Magnetic Field: The region around a magnet where magnetic force can be experienced.

Properties of Magnetic Field Lines:

Magnetic field lines never intersect each other.
They form closed loops.
Outside the magnet, direction is North pole to South pole.
Inside the magnet, direction is South pole to North pole.

Activity: Tracing Field Lines Using Compass Needle

Place the bar magnet on a white paper and mark its boundary.
Place the compass needle near the North pole of the magnet.
Mark the position of the two ends of the needle.
Move the needle to a new position.
Continue step by step till you reach the South pole.
Join the points marked on the paper. This curve represents a magnetic field line.

Why do two magnetic field lines never intersect?
If two field lines cross each other, the compass needle would show two directions at the point of intersection, which is not possible.

Right-Hand Thumb Rule

Hold the current-carrying conductor in your right hand.
Thumb points in the direction of current.
Four fingers wrapped around the conductor show the direction of magnetic field.

Direction of Current	Magnetic Field Direction
Upward	Anticlockwise
Downward	Clockwise

Solenoid and Electromagnet

Solenoid: A circular coil of insulated copper wire.

Magnetic field in a solenoid is the same as that of a bar magnet.
Inside the solenoid, the magnetic field is uniform.
When a soft iron core is placed inside a solenoid, it is converted into an electromagnet.

Strength of magnetic field in a solenoid increases by:

Increasing current.
Increasing the number of turns of the coil.

Magnetic Field in a Circular Loop: Magnetic field lines are circular around the loop and nearly straight at the centre.

Fleming's Left-Hand Rule

Finger	Represents
Thumb	Motion / Force
Forefinger	Magnetic Field
Middle Finger	Current

Activity: Force on Current-Carrying Conductor

An aluminium rod is placed between the poles of a horseshoe magnet.
When current is passed, the rod moves in one direction.
When current is reversed, the rod moves in the opposite direction.

Domestic Electric Circuits and Hazards

Short Circuit: When live wire and neutral wire come in direct contact, it causes a short circuit.

Overloading: Connecting too many devices to a single socket or a sudden hike in voltage may cause overloading.

Prevention of Short Circuit and Overloading

Use good-quality wires.
Use a fuse.
Do not connect many devices to a single socket.
Do not use faulty devices.

Functions of Earth Wire

Provides a low-resistance path.
Sends leakage current to the ground.
Prevents electric shock to the user.

⭐ Quick Revision – Magnetic Effects

Magnetic field lines never intersect.
Outside magnet: North to South.
Inside magnet: South to North.
Right-hand thumb rule gives magnetic field direction.
Soft iron core is used in an electromagnet.
Fleming's left-hand rule gives force direction.
Earth wire protects from electric shock.

3. LIGHT – REFLECTION AND REFRACTION

Reflection of Light and Laws

Reflection of Light: Bouncing back of light when light falls on a reflecting surface.

Laws of Reflection:

Angle of incidence = Angle of reflection (i = r).
Incident ray, reflected ray and normal all lie on the same plane.

Important Terms in Spherical Mirrors

Pole (P): Centre of the spherical mirror.

Centre of Curvature (C): Centre of the sphere of which the mirror forms a part.

Principal Focus of Concave Mirror (F): Incident rays parallel to the principal axis after reflection actually meet at a point.

Principal Focus of Convex Mirror (F): Incident rays parallel to the principal axis after reflection appear to meet at a point.

Principal Axis: Line passing through C and P.

Radius of Curvature (R): Distance between C and P. R = 2f.

Focal Length (f): Distance between F and P.

Concave and Convex Mirrors

Concave Mirror	Convex Mirror
Reflecting surface curved inwards.	Reflecting surface curved outwards.
Converging mirror.	Diverging mirror.
Can form real and inverted images.	Forms virtual and erect images.
Focal length negative (−ve).	Focal length positive (+ve).
Torches, search lights, vehicle headlights, shaving mirrors, dentist mirrors and solar furnaces.	Rear-view mirrors in vehicles because they give erect and diminished images.

Mirror Formulas

Mirror Formula1/v + 1/u = 1/f

Magnificationm = h'/h = −v/u

Radius of CurvatureR = 2f

Refraction of Light and Laws

Refraction of Light: Bending of light when light travels from one medium to another.

Rarer to denser medium – bends towards the normal.
Denser to rarer medium – bends away from the normal.
Light travels faster in a rarer medium than in a denser medium.

Laws of Refraction:

Incident ray, refracted ray and normal all lie on the same plane.
sin i / sin r = Constant (Snell's Law).

Convex and Concave Lenses

Convex Lens	Concave Lens
Thicker in the middle and thinner at the edges.	Thicker at the edges and thinner in the middle.
Converging lens.	Diverging lens.
Can form real and inverted images.	Forms virtual and erect images.
Focal length positive (+ve).	Focal length negative (−ve).

Refractive Index, Lens Formula and Magnification

Refractive Index: Ratio of speed of light in air to speed of light in a medium.
n = c/v

Higher refractive index – medium is optically denser and speed of light decreases.
Lower refractive index – medium is optically rarer and speed of light increases.
Refractive index of diamond is 2.42.

Lens Formula1/v − 1/u = 1/f

Magnificationm = h'/h

Refractive Indexn = c/v

Magnification:

Positive – Virtual and erect image.
Negative – Real and inverted image.
m greater than 1 – Magnified image.
m less than 1 – Diminished image.
m = 1 – Same-size image.

Power of Lens

Power of a lens is the reciprocal of its focal length in metres.
P = 1/f

SI unit – Dioptre (D).
1 dioptre is the power of a lens whose focal length is 1 metre.
Power of convex lens is positive (+ve).
Power of concave lens is negative (−ve).

⭐ Quick Revision – Light

Law of reflection: i = r.
Concave mirror: Converging mirror.
Convex mirror: Diverging mirror.
Mirror formula: 1/v + 1/u = 1/f.
Lens formula: 1/v − 1/u = 1/f.
Refractive index: n = c/v.
Power of lens: P = 1/f.
SI unit of power: Dioptre.

4. HUMAN EYE AND COLOURFUL WORLD

Human Eye Parts and Accommodation

Part	Function
Pupil	Controls the amount of light entering the eye.
Iris	Controls the size of the pupil.
Ciliary Muscles	Change the focal length of the eye lens.
Retina	Screen on which image is formed.

Power of Accommodation: Ability of the eye to see near and far objects by changing its focal length.

Accommodation of Eye

Near Objects	Distant Objects
Ciliary muscles contract.	Ciliary muscles relax.
Lens becomes thick.	Lens becomes thin.
Focal length decreases.	Focal length increases.

Near Point: 25 cm.
Far Point: Infinity.

Defects of Vision and Corrections

Defect	Problem	Causes	Correction
Myopia Nearsightedness	Cannot see distant objects clearly.	Excessive curvature of eye lens; elongation of eyeball.	Concave lens.
Hypermetropia Farsightedness	Cannot see near objects clearly.	Focal length of eye lens is too long; eyeball is too small.	Convex lens.
Presbyopia	Difficulty seeing near or far objects clearly.	Weakening of ciliary muscles; decreasing flexibility of eye lens.	Bifocal lens.
Cataract	Eye lens becomes milky and cloudy in old age.	Clouding of the eye lens.	Surgery.

Atmospheric Phenomena and Light Effects

Dispersion: Splitting of white light into seven colours. The band of seven colours is called the spectrum.

Important:

Red bends the least.
Violet bends the most.

Rainbow Formation: Caused by dispersion of sunlight by tiny water droplets in the atmosphere acting like small prisms, combined with internal reflection.

Twinkling of Stars: Due to atmospheric refraction of starlight caused by continuously changing refractive index of air layers.

Why Planets Do Not Twinkle: Planets do not twinkle because they are closer to Earth and act as extended sources of light which nullify the twinkling effect.

Tyndall Effect: Path of light becomes visible due to scattering of light by colloidal particles.

Why Does the Sky Appear Blue? Atmospheric fine particles scatter blue light more strongly because blue light has a shorter wavelength than red light.

⭐ Quick Revision – Human Eye and Colourful World

Near point – 25 cm.
Far point – Infinity.
Myopia – Concave lens.
Hypermetropia – Convex lens.
Presbyopia – Bifocal lens.
Cataract – Surgery.
Dispersion – Splitting of white light.
Red bends least.
Violet bends most.
Twinkling of stars – Atmospheric refraction.
Blue sky – Scattering of light.

Human Eye And Colourful World

MG SCHOOL SCIENCE • CLASS 10

SCIENCE LEARNING SLIDES

Chapter: The Human Eye and the Colourful World

Class 10 • Physics • Light

The Human Eye &
the Colourful World

Explore how the eye focuses light, how spectacles correct vision, and how prisms and the atmosphere create the colours and optical effects we observe every day.

Human eyeDefects of visionPrism & dispersionAtmospheric refractionScattering

👁️

＋

🌈

＋

🔺

Learning goal: Understand the working of the human eye and explain important natural phenomena involving light.

01 • Introduction

How do we see the world?

Light rays from an object enter our eyes. The eye lens focuses the light to form an image on the retina. The retina sends electrical signals to the brain through the optic nerve, and the brain interprets them.

Object

→

Eye lens

→

Retina

→

Optic nerve

→

Brain

📷

Camera analogy

The eye works like a camera: its lens focuses incoming light to form an image.

🧠

Image interpretation

The retina converts light into electrical signals; the brain interprets these signals.

02 • Structure of the eye

The human eye: important parts

Light path:

Cornea → pupil → eye lens → retina

Simplified teaching illustration; not to scale.

Cornea

Transparent front membrane. Most refraction of entering light occurs at its outer surface.

Iris & pupil

The iris controls pupil size. The pupil regulates the amount of light entering the eye.

Crystalline lens

A convex lens that provides fine adjustment to focus objects on the retina.

Retina

Light-sensitive layer containing cells that generate electrical signals.

Optic nerve

Carries electrical signals from the retina to the brain.

Ciliary muscles

Change the shape of the eye lens to adjust its focal length.

Remember: The eyeball is roughly spherical and has a diameter of about 2.3 cm.

03 • Accommodation

Power of accommodation

The ability of the eye lens to change its focal length to see objects clearly at different distances is called accommodation.

🏔️

Distant object

Ciliary muscles relax.
Lens becomes thinner.
Focal length increases.

📖

Nearby object

Ciliary muscles contract.
Lens becomes thicker.
Focal length decreases.

Vision point	Meaning	Normal adult eye
Near point	Minimum distance for clear vision without strain	25 cm
Far point	Farthest point visible clearly	Infinity (∞)

Cataract: The crystalline lens may become milky and cloudy, causing partial or complete loss of vision. Vision can be restored by surgery to replace it with an artificial intraocular lens.

04 • Defects of vision

Myopia and hypermetropia

Myopia • Near-sightedness

Nearby objects are clear; distant objects are blurred. The image of a distant object forms in front of the retina.

Causes: excessive curvature of the eye lens or elongation of the eyeball.

Correction: Concave lens of suitable power.

Hypermetropia • Far-sightedness

Distant objects are clear; nearby objects are blurred. The image of a nearby object forms behind the retina.

Causes: focal length of eye lens too long or eyeball too small.

Correction: Convex lens of suitable power.

Myopia

→

Concave lens

Hypermetropia

→

Convex lens

05 • Defects of vision

Presbyopia & bifocal lenses

Presbyopia is an age-related defect in which the power of accommodation decreases. The near point gradually moves farther away, making nearby objects difficult to see clearly.

Causes

Gradual weakening of ciliary muscles.
Decreasing flexibility of the eye lens.

Correction

Convex lens of suitable power.
Bifocal lenses may be needed when myopia and hypermetropia occur together.

Upper part
Concave lens
👀 Distant vision

Lower part
Convex lens
📖 Near vision

Bifocal lens: The upper part contains a concave lens for distant vision; the lower part contains a convex lens for near vision.

06 • Refraction through a prism

How does a glass prism bend light?

A triangular glass prism has two triangular bases and three rectangular lateral surfaces. A ray entering from air into glass bends towards the normal. On emerging from glass into air, it bends away from the normal.

Incident ray

↘

Glass prism 🔺

↘

Emergent ray

Angle of a prism

The angle between two adjoining lateral surfaces of the prism.

Angle of deviation (D)

The angle between the directions of the incident ray and the emergent ray.

07 • Dispersion

Splitting of white light

When white light passes through a glass prism, it splits into a band of seven colours. This phenomenon is called dispersion. The band of colours is called the spectrum.

VIBGYOR

Violet • Indigo • Blue • Green • Yellow • Orange • Red

Red light

Has the longest wavelength among visible colours and is deviated the least.

Violet light

Has the shortest wavelength among visible colours and is deviated the most.

Why does dispersion occur? Different colours are deviated through different angles in a glass prism, so they emerge along separate paths.

08 • Recombination & rainbow

White light returns — and nature makes a rainbow

🔺

Recombination of white light

Isaac Newton showed that sunlight is made of seven colours. An identical inverted prism can recombine the spectrum to produce white light.

🌈

Rainbow formation

Raindrops act as tiny prisms. Sunlight is refracted, dispersed, internally reflected and refracted again as it emerges.

Sunlight

→

Water droplet

→

🌈 Colours

Observation: A rainbow appears in the direction opposite to the Sun, usually after a rain shower.

09 • Atmospheric refraction

Light bends in the atmosphere

Atmospheric refraction is the refraction of light by different layers of the atmosphere. It explains several everyday observations.

Twinkling of stars

Changing atmospheric conditions continuously refract starlight. Since stars are point sources, their apparent brightness fluctuates.

Planets do not twinkle

Planets are extended sources. Fluctuations from different parts average out, so their overall brightness remains relatively stable.

Advanced sunrise

Atmospheric refraction makes the Sun appear about two minutes before actual sunrise.

Delayed sunset

The Sun remains visible for about two minutes after actual sunset because its rays bend through atmospheric layers.

Stars near the horizon

They appear slightly higher than their actual position due to atmospheric refraction.

Apparent flickering

Objects behind a hot surface may appear to flicker because changing air density changes the path of light.

10 • Scattering of light

Tyndall effect & the blue sky

Tyndall effect

The scattering of light by colloidal particles is called the Tyndall effect. It makes the path of a beam visible in a smoky room or misty forest.

Scattering and particle size

Very fine particles mainly scatter blue light. Larger particles scatter longer wavelengths; sufficiently large particles may scatter light that appears white.

Sunlight

→

Fine air molecules

→

More blue scattering

Why is the clear sky blue? Air molecules and very fine particles scatter shorter wavelengths, such as blue, more effectively than longer wavelengths, such as red. The scattered blue light makes the sky appear blue.

Extra facts: Red light has a wavelength approximately 1.8 times that of blue light. Without an atmosphere, the sky would appear dark. At very high altitudes, less scattering makes the sky appear darker.

11 • Quick revision

Chapter at a glance

Topic	Key point to remember
Accommodation	Eye lens changes focal length with help of ciliary muscles.
Near point / Far point	25 cm / Infinity for a normal adult eye.
Myopia	Image in front of retina; corrected by concave lens.
Hypermetropia	Image behind retina; corrected by convex lens.
Presbyopia	Reduced accommodation with age; convex or bifocal lens.
Dispersion	White light splits into VIBGYOR; violet deviates most, red least.
Rainbow	Refraction, dispersion and internal reflection in raindrops.
Twinkling	Atmospheric refraction of starlight.
Blue sky	Shorter wavelengths are scattered more by fine particles.

12 • Check your understanding

Quick knowledge check

1. Which lens is used to correct myopia?

Correct! Myopia is corrected using a concave lens of suitable power.

2. Which colour deviates the most through a glass prism?

Correct! Violet light is deviated the most; red is deviated the least.

3. What is the near point of a normal adult eye?

Correct! The near point of a normal adult eye is 25 cm.

Select an option to check the answer. Review the slides and try again.

13 • End of lesson

Keep observing the world!

From the focusing power of our eyes to the colours of a rainbow and the blue sky, light helps explain many wonderful phenomena around us.

👁️ 🌈 ☀️

MG SCHOOL SCIENCE
Learn • Explore • Understand • Achieve

Study material adapted from the supplied Class 10 chapter notes: “The Human Eye and the Colourful World”.

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Sunday, 8 November 2026