Free Download CBSE Papers: Class 10 Science - Sample Papers, Important Questions, Notes

TERM - I

Theme: Materials

Unit I : Chemical Substances - Nature and Behaviour

Chapter - 1 Chemical reactions and equations

Chemical Reactions: Chemical equation, Balanced chemical equation, implications of a balanced chemical equation, types of chemical reactions: combination, decomposition, displacement, double displacement, precipitation, neutralization, oxidation and reduction.

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Atomic Physics Question Bank Class 10 - ICSE Board

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Handwritten Notes Heredity and Evolution Class 10 Science

Handwritten Notes How do Organisms Reproduce Class 10 Science

Handwritten Notes Control and Coordination Class 10 Science

Chapter - 2 Acids, Bases and Salts

Adam, Bases and Salts: Their definitions in terms of furnishing of H+ and OHions, General properties, examples and uses, concept of pH scale (Definition relating to logarithm not required), importance of pH everyday life; preparation and uses of Sodium Hydroxide, Bleaching powder, Baking soda, Washing soda and Plaster of Paris.

Chapter - 3 Metals and Non-metals

Metal and Non-metals: Properties of metals and non-metals; Reactivity series; Formation and properties of ionic compounds
Theme: The World of the Living

Unit II : World of Living

Chapter - 6 Life Processes

Life processes: ‘Living Being’. Basic concept of nutrition, respiration, transport and excretion in plai and animals.

Theme: How Things Work

Unit III: Natural Phenomena

Chapter - 10 Light, Reflection and Refraction Reflection of Light by Curved Surfaces:

Images formed by spherical mirrors, centre of curvature, principal axis, principal focus, focal length, mirror formula (Derivation not required), magnification. Refraction; Laws of refraction, refractive index. Refraction of light by spherical lens; Image formed by spherical lenses; Lens formula (Derivation not required); Magnification. Power of a lens.

Chapter - 11 Human Eve and Colourful World

Refraction of light through a prism, dispersion of light, scattering of light, applications in daily life

TERM - II

Theme: Materials

Unit I : Chemical Substances - Nature and Behaviour

Chapter - 4 Carbon and its Compounds

Carbon Compounds: Covalent bonding in carbon compounds. Versatile nature of carbon.Homologous series.

Handwritten Notes Life Process Class 10 Science

Handwritten Notes Source of Energy Class 10 Science

Handwritten Notes Light Reflection and Refraction Class 10 Science

Handwritten Notes Carbon and its Compound Class 10 Science

Handwritten Notes Periodic Classification of Elements Class 10 Science

Handwritten Notes Some Basic Concepts of Chemistry Class 10 Science

Handwritten Notes Human Eye and Colourful World Class 10 Science

Acids Bases and Salts CBSE Class 10 Notes Chapter 2

Metals and Non-metals Class 10 Notes Science Chapter 3

Carbon and its Compounds Class 10 Notes Science Chapter 4

Periodic Classification of Elements Class 10 Notes Science Chapter 5

Chapter - 5 Periodic Classification of Elements

Periodic Classification of Elements: Need for classification, early attempts at classification of elements (Dobereiner’s Triads, Newland’s Law of Octaves, Mendeleev’s Periodic Table), Modern periodic table, gradation in properties, valency, atomic number, metallic and non-metallic properties.

Theme: The World of the Living

Unit II : World of Living

Chapter - 8 How do Organisms Reproduce?

Reproduction: Reproduction in animals and plants (asexual and sexual) reproductive health-need and methods of family planning. Safe sex vs HIV/AIDS. Child bearing and women’s health.

Chapter - 9 Heredity and Evolution

Heredity: Heredity; Mendel’s contribution- Laws for inheritance of traits: Sex determination: brief introduction;

Theme: Natural Phenomena

Unit IV : Effects of Current

Chapter - 12 Electricity Ohm’s law; Resistance, Resistivity. Factors on which the resistance of a conductor depends. Series combination of resistors, parallel combination of resistors And its applications in daily life, Heating effect of electric current and its applications in daily life. Electric power, Interrelation between P, V, I and R.

Chapter - 13 Magnetic Effects of Current

Magnetic Effects of Current: Magnetic field, field lines, field due to a current carrying conductor, field due to current carrying coil or solenoid; Force on current carrying conductor, Fleming’s Left Hand Rule, Electric Motor, Electromagnetic induction. Induced potential difference, Induced current. Fleming’s Right Hand Rule.

Theme: Natural Resources

Unit V : Natural Resources

Chapter - 15 Our Environment

Our Environment: Eco-system, Environmental problems, Ozone depletion, waste production and their solutions. Biodegradable and non-biodegradable substances.

Life Process Class 10 Notes Science Chapter 6

Control and Coordination Class 10 Notes Science Chapter 7

How do Organisms Reproduce Class 10 Notes Science Chapter 8

Heredity and Evolution Class 10 Notes Science Chapter 9

Light Reflection and Refraction Class 10 Notes Science Chapter 10

Human Eye and Colourful World Class 10 Notes Science Chapter 11

Electricity Class 10 Notes Science Chapter 12

Magnetic Effects of Electric Current Class 10 Notes Science Chapter 13

Sources of Energy Class 10 Notes Science Chapter 14

Our Environment Class 10 Notes Science Chapter 15

Management of Natural Resources Class 10 Notes Science Chapter 16

CBSE Class 10 Biology Pre Board Question Paper

CBSE Class 10 Biology Half Yearly Question Paper - DPS

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CBSE Class 10 Half Yearly Biology Questions - DPS

PRACTICALS

Practical should be conducted alongside the concepts taught in theory classes.

TERM - I

List of Experiments

1. A. Finding the pH of the following samples by using pH paper/universal indicator:

(i) Dilute Hydrochloric Acid

(ii) Dilute NaOH solution

(iii) Dilute Ethanoic Acid solution

(iv) Lemon juice

(v) Water

(vi) Dilute Hydrogen Carbonate solution

B. Studying the properties of acids and bases (HC1 & NaOH) on the basis of their reaction with:

(a) Litmus solution (Blue/Red)

(b) Zinc metal

Unit I : Chapter-2

2. Performing and observing the following reactions and classifying them into:

A. Combination reaction

B. Decomposition reaction

C. Displacement reaction

D. Double displacement reaction

(i) Action of water on quicklime

(ii) Action of heat on ferrous sulphate crystals (Hi) Iron nails kept in copper sulphate solution

(iv) Reaction between sodium sulphate and barium chloride solutions.

Unit I : Chapter - 1

3. A. Observing the action of Zn, Fe, Cu and Al metals on the following salt solutions:

(i) ZnSO4 (aq)

(ii) FeSO4 (aq)

(iii)CuSO4 (aq)

(iv) Al2 (SO4)3 (aq)

B. Arranging Zn, Fe, Cu and Al (metals) in the decreasing order of reactivity based on the above result.

Unit I : Chapter - 3

4. Experimentally show that carbon dioxide is given out during respiration.

Unit II : Chapter - 6

5. Determination of the focal length of (t) Concave mirror and (ii) Convex lens by obtaining the image of a distant object.

Unit III : Chapter - 10

6. Tracing the path of a ray of light passing through a rectangular glass slab for different angles of f incidence. Measure the angle of incidence, angle of refraction, angle of emergence and Interpret the result.

Unit Ill : Chapter-10

7. Tracing the path of the rays of light through a glass prism.

Unit III : Chapter - 11

CBSE Class X Biology Test Papers 2020 - DPS

CBSE Class X Biology Test Question Papers 2020 - DPS

CBSE Class 10 Biology Sample Test Papers - DPS

CBSE Class 10 Biology Periodic Test Papers - DPS

CBSE Class 10 Science HOTS Question Management of Natural Resources

CBSE Class 10 Biology HOTS Question Our Environment

CBSE Class 10 Biology HOTS Question Heredity and Evolution

CBSE Class 10 HOTS Question How Do Organisms Reproduce

CBSE Class 10 Science Control and Coordination HOTS Questions

CBSE Class 10 Biology Life Processes HOTS Questions

Carbon and its Compounds Class 10 Notes Science Chapter 4

Acids Bases and Salts Class 10 Notes Science Chapter 2

TERM - II

List of Experiments

1. Studying the dependence of Potential difference (V) across a resistor on the current (I) passing through it and determining its resistance. Also plotting a graph between V and I

Unit IV : Chapter - 12

2. Studying (a) binary fission in Amoeba, and (b) budding in yeast and Hydra with the help of prepared slides.

Unit II : Chapter - 8

Prescribed Books

 Science-Textbook for class IX-NCERT Publication

 Science-Text book for class X- NCERT Publication

 Assessment of Practical Skills in Science-Class IX - CBSE Publication

 Assessment of Practical Skills in Science- Class X- CBSE Publication

 Laboratory Manual-Science-Class IX, NCERT Publication

 Laboratory Manual-Science-Class X, NCERT Publication

 Exemplar Problems Class IX - NCERT Publication

 Exemplar Problems Class X - NCERT Publication

CHAPTER – 1

CHEMICAL REACTIONS AND EQUATIONS

CHEMICAL REACTIONS

Any change can be classified as physical change and chemical change. Physical changes can be easily reversed but, it is not easy to reverse a chemical change.

In chemical changes, new substances are formed and it is difficult to regenerate the original substances. Chemical changes are more permanent than physical changes.

Chemical reaction involves chemical changes.

Chemical reactions are the processes in which new substances with new properties are formed.

During a chemical reaction, atoms of one element do not change into those of another element.

Only a rearrangement of atoms takes place in a chemical reaction.

Magnesium ribbon burns with a dazzling white flame and changes into a white powder. This

powder is magnesium oxide. It is formed due to the reaction between magnesium and oxygen present in the air.

Magnesium Oxygen Magnesium Oxide

Heat

(As ribbon) (From air) (White powder)

 

The burning of magnesium in air to form magnesium oxide is an example of chemical reaction.

REACTANTS AND PRODUCTS

The substances which take part in a chemical reaction are called reactants. The new substances produced as a result of chemical reaction are called products.

In the above chemical reaction, there are two reactants : Magnesium and Oxygen but only one

product : Magnesium oxide.

CHARACTERISTICS OF CHEMICAL REACTIONS

In a chemical reaction, reactants are transformed into products. The important characteristics of chemical reaction are:

 Evolution of a gas

 Formation of a precipitate

 Change in colour

 Change in temperature and

 Change in state.

Any one of these characteristics can tell us whether a chemical reaction has taken place or not.

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VERY SHORT ANSWER TYPE QUESTIONS

1. How are chemical reactions expressed in the shortest way?

2. What is the type of reaction in which the reactant gives simpler products?

3. What is the type of reaction in which two or more reactants combine to a give a single product?

4. In which type of reaction does an exchange of partners take place?

5. Why are chemical equations balanced?

6. What symbol is used to indicate a solution made in water?

7. What type of reaction does occur during the digestion of food inside our body?

SHORT ANSWER TYPE QUESTIONS

1. What do you mean by a Chemical reaction? Give an example of a chemical reaction.

2. What do you mean by a combination reaction? Give an example.

3. What do you mean by a displacement reaction? Give an example.

4. What do you mean by a decomposition reaction? Give an example.

5. What do you mean by a double displacement reaction? Give an example.

6. Explain the term “Electrolytic decomposition”, giving a suitable example.

7. Mention any two uses of decomposition reaction.

CHAPTER – 2 ACIDS, BASES AND SALTS

ACIDS

Acid is a substance which furnishes H+ ions or H3O + ions when dissolved in water. Acids have one or more replaceable hydrogen atoms. The word acid is derived from the Latin name ‘acidus’ which means sour taste. Substances with ‘sour taste’ are acids. Lemon juice, vinegar and grape juice have sour taste, so they are acidic. They change blue litmus to red. They are colourless with phenolphthalein and pink with methyl orange. There are many substances which contain acid and hence taste sour, such as curd, tamarind, lemon, etc.

CLASSIFICATION OF ACIDS

1. Based on their sources : Acids are classified into two types namely organic acids and inorganic acids. Organic acids:- Acids present in plants and animals (living beings) are organic acids eg. HCOOH, CH3COOH (Weak acids).

Inorganic acids:- Acids from rocks and minerals are inorganic acids or mineral acids eg.

HCl, HNO3, H2SO4 (Strong acids).

2. Based on their basicity

Monobasic acid: - It is an acid which gives one hydrogen ion per molecule of the acid in solution eg. HCl, HNO3.

Dibasic acid:- It is an acid which gives two hydrogen ions per molecule of the acid in solution e.g., H2SO4, H2CO3.

Tribasic acid:- It is an acid which gives three hydrogen ions per molecule of the acid in solution. e.g.,H3PO4,

3. Based on ionisation

Acids are classified into two types based on ionisation.

Strong acids:- These are acids which ionise completely in water eg.HCl

Weak acids:-These are acids which ionise partially in water eg. CH3COOH

4. Based on concentration:- Depending on the percentage or amount of acid dissolved in water acids are classified into concentrated acid and dilute acid.

Concentrated acid:- It is an acid having a relatively high percentage of acid in its aqueous solution.

Dilute acid:- It is an acid having a relatively low percentage of acid in aqueous solution.

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NATURAL INDICATOR

Indicators obtained from natural sources are called natural indicators. Litmus, turmeric, red cabbage, China rose, etc. are some common natural indicators used widely to show the acidic or basic character of substances.

LITMUS

Litmus is obtained from lichens. The solution of litmus is purple in colour. Litmus paper comes in two colour – blue and red.

 An acid turns blue litmus paper red.

 A base turns red litmus paper blue.

TURMERIC

Turmeric is another natural indicator. Turmeric is yellow in colour. Turmeric solution or paper turns reddish brown with base. Turmeric does not change colour with acid.

RED CABBAGE

The juice of red cabbage is originally purple in colour. Juice of red cabbage turns reddish with acid and turns greenish with base.

OLFACTORY INDICATORS

Substances which change their smell when mixed with acid or base are known as olfactory indicators. For example onion, vanilla, clove, etc.

ONION

Paste or juice of onion loses its smell when added with base. It does not change its smell with acid.

VANILLA

The smell of vanilla vanishes with base, but it’s smell does not vanishes with an acid. Olfactory indicators are used to ensure the participation of visually impaired students in laboratory.

SYNTHETIC INDICATOR

Indicators that are synthesized in laboratory are known as synthetic indicators. For example; phenolphthalein, methyl orange, etc. Phenolphthalein is a colourless liquid. It remains colourless with acid but turns into pink with a base.

UNIVERSAL INDICATOR: Using a litmus paper, phelophthalein, methyl orange, etc. only the acidic or basic character of a solution can be determined, but use of these indicators does not give the idea about the strength of acid or base. So, to get the strength as well as acidic and basic nature of a given solution universal indicator is used. Universal indicator shows different colour over the range of pH value from 1 to 14 for a given solution. Universal indicator is available both in the form of strips and solution. Universal indicator is the combination of many indicators, such as water, propanol, phelophthalein, sodium salt, sodium hydroxide, methyl red, bromothymol blue monosodium salt, and thymol blue monosodium salt. The colour matching chart is supplied with universal indicator which shows the different colours for different values of pH.

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VERY SHORT ANSWER TYPE QUESTIONS

1. Name two natural indicators.

2. Name two indicators that are usually used in chemical laboratories to indicate acidic/basic

nature of a solution.

3. What is the general name of bases that are soluble in water?

4. What is an acid?

5. Define base

6. What is the action of an acid on blue litmus paper?

7. Name two natural substances that contain acid.

8. What is the oxide of a metal called?

9. Are all bases alkalis?

10. Which type of substance is used to indicate an acid or a base?

11. What is the common element present in all acids?

12. Give the name and formula of two mineral acids.

13. Common salt contains a substance which is hygroscopic. Name the substance and write its formula.

14. Name any two organic acids.

15. What is the common to all bases?

16. Name two sources of common salt.

17. How do metals react with acid?

18. Name two metals that react with a base to produce hydrogen gas.

19. Which gas is evolved when sodium carbonate reacts with hydrochloric acid?

20. What happens when carbon dioxide gas is passed into lime water?

21. Name a sodium compound which loses its water of crystallization on exposure to air.

22. A compound of metal is obtained mainly from sea water. Write the name and formula of the compound.

23. What is the common name and formula of sodium hydroxide?

24. What is the reaction called in which an acid and a base nullify the effect of each other?

25. Name the salt which was an important symbol in India’s struggle for freedom?

26. Name a sodium compound used as a cleansing agent for domestic purposes.

27. Why does and aqueous solution of an acid conduct electricity?

28. The pH of a solution is 4. What is the nature of the solution?

29. A solution reacts with crushed egg-shells to give a gas that turns lime water milky. Say, whether the solution contains an acid or a base.

30. Which type of medicine is used to treat indigestion?

31. Which compound of a metal is a constituent of many dry soap powders?

32. Name the acid which is used as a bathroom cleaner.

33. What is the action of litmus on an aqueous solution of ammonium chloride?

34. Why is a basic substance used to treat a honey-bee sting?

35. A solution turns blue litmus re. What is it pH value?

36. Which one is more acidic, pH = 2 or pH = 5?

37. Which one of the two solutions is more basic, pH = 8 or pH = 11?

38. What is the nature of the salt which dissolves in water to produce a solution which turns blue litmus to red?

39. A milkman adds some baking soda to fresh milk. How will the pH of the fresh milk change?

40. What is the pH of a solution which is neither acidic nor basic?

41. What is the chemical formula of common salt?

42. Name the process by which sodium hydroxide is made by electrolysis of brine?

43. Give the chemical name and formula of washing soda?

44. Mention the property of sodium carbonate that makes it useful as an ingredient for dry soap powders.

45. Name the carbonate of a metal which is soluble in water.

46. What is soda ash?

47. State whether the aqueous solution of washing soda is acidic or alkaline?

48. Name the substance which on being treated with chlorine yields bleaching powder.

49. Write the chemical formula of plaster of paris.

50. Write an equation to show the reaction between plaster of paris and water.

51. Write the chemical formula of quicklime.

52. Name a compound of calcium which is used for whitewashing.

53. Which compound of calcium is used for making cement and glass?

54. Write an equation to show the reaction between quicklime and water.

55. Which compound of calcium is used to produce limelight?

56. Write the chemical name and formula of baking soda?

57. Name a compound of sodium which is used in fire extinguisher.

58. Write the chemical name and formula of bleaching powder?

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CHAPTER – 3 METALS AND NON-METALS

Metals occupy the bulk of the periodic table, while non-metallic elements can only be found on the right-hand-side of the Periodic Table . A diagonal line, drawn from boron (B) to polonium (Po), separates the metals from the nonmetals. Most elements on this line are metalloids, sometimes called semiconductors. This is because these elements exhibit electrical properties intermediate to both, conductors and insulators. Elements to the lower left of this division - line are called metals, while elements to the upper right of the division - line are called non-metals.

On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a nonmetal.

PHYSICAL PROPERTIES OF METALS:

 Physical state - Metals are solids at room temperature e.g. sodium, aluminium, potassium, magnesium. There are exceptions to this. Mercury and gallium are metals but they are in liquid state at room temperature.

 Luster – Metals have a shining surface called luster when freshly prepared. They have a quality of reflecting light from their surface and they can be polished e.g. metals like gold, silver, copper show this property.

 Malleability - Metals can be beaten into thin sheets. This property is called malleability. Due to this property, metals can be rolled into sheets e.g. aluminium, copper, zinc can be beaten into sheets.

 Ductility - Metals can be drawn into thin wires. This property is called ductility. For example, 100 grams of silver can be drawn into a thin wire about 200 meters long.

 Hardness – Metals are generally hard e.g. iron, cobalt, nickel. There are few exceptions to this. Sodium and potassium are soft and they can be cut with a knife.

 Sound: Metals produce ringing sound, so, metals are called sonorous. Sound of metals is also known as metallic sound. This is the cause that metal wires are used in making musical instruments.

 Conduction – Generally, metals are good conductors of heat and electricity because they have free electrons. Silver and copper are the two best conductors . Relatively, lead and bismuth are poor conductors of heat and electricity.

 Density - Metals generally have high density and they are heavy. Iridium and osmium have the highest densities while lithium has the lowest density.

 Melting and boiling point – Metals usually have high melting point and boiling point. For example, iron, cobalt and nickel have high melting and boiling point. Tungsten has the highest melting point. There are some exceptions to this. For example , most of the alkali metals have low melting and boiling point.

 Strength: Most of the metals are strong and have high tensile strength. Because of this big structures are made using metals, such as copper and iron.

 Color: Most of the metals are grey in color. But gold and copper are exceptions

CHAPTER – 6 LIFE PROCESSES

LIFE PROCESS

The maintenance of living organisms must go on even at the conditions, when they are not physically active. Even when we sit idle and during sleeping, this maintenance job through cells functioning has to go on. The life process includes the activities performed by the different organs to maintain the body. Some of the life processes in the living beings are described below:

 Nutrition

The process of obtaining energy through consumption of food is called as nutrition.

 Respiration

The process of acquiring oxygen through breathing and make it available to cells for the process of breaking down of organic substances into simpler compounds is called as respiration.

 Transportation

Transportation is the process by which the food and oxygen is carried from one organ to other organs in the body.

 Excretion

It is the process by which the metabolic waste by-products are removed from the different organs and released out from the body.

Question 1: Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?

Answer : Multicellular organisms such as humans possess complex body designs. They have specialised cells and tissues for performing various necessary functions of the body such as intake of food and oxygen. Unlike unicellular organisms, multicellular cells are not in direct contact with the outside environment. Therefore, diffusion cannot meet their oxygen requirements.

Question 2: What criteria do we use to decide whether something is alive?

Answer : Any visible movement such as walking, breathing, or growing is generally used to decide whether something is alive or not. However, a living organism can also have movements, which are not visible to the naked eye. Therefore, the presence of life processes is a fundamental criterion that can be used to decide whether something is alive or not.

Question 3: What are outside raw materials used for by an organism?

Answer : An organism uses outside raw materials mostly in the form of food and oxygen. The raw materials required by an organism can be quite varied depending on the complexity of the organism and its environment.

Question 4: What processes would you consider essential for maintaining life?

Answer : Life processes such as nutrition, respiration, transportation, excretion, etc. are essential for maintaining life.

CHAPTER - 10 LIGHT – REFLECTION AND REFRACTION

LIGHT

An object reflects light that falls on it. This reflected light when received by our eyes, enables us to see things.

Reflection of light

Reflection of light is the phenomenon of bouncing back of light in the same medium on striking the surface of any object.

There are two types of reflection:

1. Regular reflection or Specular Reflection

2. Irregular reflection or Diffuse Reflection

Regular Reflection: When the reflecting surface is smooth and well polished, the parallel rays falling on it are reflected parallel to one another, the reflected light goes in one particular direction. This is Regular reflection or Specular reflection see below figure.

Irregular reflection: When the reflecting surface is rough, the parallel rays falling on it reflected in different direction, as shown in below fig. Such a reflection is known as diffuse reflection or irregular reflection.

LAWS OF REFLECTION OF LIGHT

According to the laws of Reflection of light,

(i) The angle of incidence is equal to the angle of reflection, and

(ii) The incident ray, the normal to the mirror at the point of incidence and the

reflected ray, all lie in the same plane.

These laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces.

OBJECTS

Anything which gives out light rays either its own or reflected by it is called an object.

LUMINOUS OBJECTS: The objects like the sun, other stars, electric bulb, tubelight etc. which emit their own light are called luminous objects.

NON – LUMINOUS OBJECTS: The objects which do not emit light themselves but only reflect or scatter the light which falls on them, are called non-luminous objects. A flower, chair table, book, trees, etc are all non-luminous objects.

IMAGES

Image is an optical appearance produced when light rays coming from an object are reflected from a mirror (or refracted through lens).

REAL IMAGE

The image which can be obtained on a screen is called a real image. In a cinema hall, we see the images of actors and actress on the screen. So, the images formed on a cinema screen is an example of real images.

VIRTUAL IMAGE

The image which cannot be obtained on a screen is called a virtual image. A virtual image can be seen only by looking into a mirror. The image of our face in a plane mirror is an example of virtual image.

LATERAL INVERSION

When an object is placed in front of a plane mirror, then the right side of object appears to become the left side of image; and the left side of object appears to become the right side of image. This change of sides of an object and its mirror image is called lateral inversion.

The phenomenon of lateral inversion is due to the reflection of light.

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SPHERICAL MIRROR A spherical mirror is that mirror whose reflecting surface is the part of a hollow sphere of glass.

The spherical mirrors are of two types:

Concave mirror and Convex mirror.

CONCAVE MIRROR: A concave mirror is that spherical mirror in which the reflection of light takes place at the concave surface (or bent-in surface).

CONVEX MIRROR: A convex mirror is that spherical mirror in which the reflection of light takes place at the convex surface (or bulging –out surface).

TERMS RELATED TO SPHERICAL MIRRORS

Centre of Curvature(C): The centre of curvature of a spherical mirror is the centre of the hollow sphere of glass of which the spherical mirror is a part. It is represented by letter ‘C’.

Pole(P): The pole of a spherical mirror is the centre of the mirror. It is represented by letter ‘P’.

Radius of Curvature(R): The radius of curvature of a spherical mirror is the radius of the hollow sphere of glass of which the spherical is a part. It is represented by the letter ‘R’.

Principal axis: The principal axis of a spherical mirror is the straight line passing through the centre of curvature C and pole P of the spherical mirror, produced on both sides.

Aperture: The aperture of a spherical mirror is the diameter of the reflecting surface of the mirror.

USES OF CONCAVE MIRRORS

1. Concave mirrors are commonly used in torches, search-lights and vehicles headlights to get powerful parallel beams of light.

2. Concave mirrors are used as shaving mirrors to see a larger image of the face.

3. The dentists use concave mirrors to see large images of the teeth of patients.

4. Concave mirrors are used as doctor’s head mirrors to focus light coming from a lamp on to the body parts of a patient to be examined by the doctor.

5. Concave dishes are used in TV dish antennas to receive TV signals from the distant communications satellite.

6. Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

USES OF CONVEX MIRRORS

Convex mirrors are commonly used as rear-view (wing) mirrors in vehicles. These mirrors are fitted on the sides of the vehicle, enabling the driver to see traffic behind him/her to facilitate safe driving. Convex mirrors are preferred because they always give an erect, though diminished, image. Also, they have a wider field of view as they are curved outwards. Thus, convex mirrors enable the driver to view much larger area than would be possible with a plane mirror.

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NUMERICALS BASED ON CONVEX AND CONCAVE MIRROR

1. Find the focal length of a convex mirror of radius of curvature 1m.

2. Focal length of a convex mirror is 50 cm. What is its radius of curvature?

3. Radius of curvature of a concave mirror is 25 cm. What is its focal length?

4. A concave mirror produces 10 cm long image of an object of height of 2cm. What is the magnification produced?

5. An object 1 cm high is held near a concave mirror of magnification 10. How tall will be the image?

6. An object 4 cm in size is placed at a distance of 25 cm from a concave mirror of focal length 15 cm. Find the position, nature and height of the image.

7. A converging mirror forms a real image of height 4 cm, of an object of height 1 cm placed 20 cm away from the mirror. Calculate the image distance. What is the focal length of the mirror?

8. A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.

9. An arrow 2.5 cm high is placed at a distance of 25 cm from a diverging mirror of focal length 20 cm., Find the nature, position and size of the image formed.

10. The image formed by a convex mirror of focal length 20cm is a quarter of the object. What is the distance of the object from the mirror?

11. Find the size, nature and position of image formed by a concave mirror, when an object of size 1cm is placed at a distance of 15cm. Given focal length of mirror is 10cm.

12. An object 2cm high is placed at a distance of 16cm from a concave mirror, which produces 3cm high inverted image. What is the focal length of the mirror? Also, find the position of the image.

13. An erect image 3 times the size of the object is obtained with a concave mirror of radius of curvature 36cm. What is the position of the object?

14. A 2.5cm candle is placed 12 cm away from a convex mirror of focal length 30cm. Give the location of the image and the magnification.

15. An object is placed in front of a concave mirror of focal length 20cm. The image formed is 3 times the size of the object. Calculate two possible distances of the object from the mirror

SPHERICAL LENSES

A lens is any transparent material (e.g. glass) of an appropriate shape that can take parallel rays of incident light and either converge the rays to a point or diverge the rays from a point. A transparent material bound by two surfaces, of which one or both surfaces are spherical, forms a lens. Some lenses will focus light rays to a single point. These lenses are called converging or concave lenses. Other lenses spread out the light rays so that it looks like they all come from the same point. These lenses are called diverging or convex lenses. Lenses change the direction of light rays by refraction. They are designed so that the image appears in a certain place or as a certain size. Lenses are used in eyeglasses, cameras, microscopes, and telescopes.

CHAPTER - 11 THE HUMAN EYE AND THE COLOURFUL WORLD

REFRACTION OF LIGHT THROUGH A PRISM

Prism is a transparent optical element, which refracts light. An optical object to be defined as prism must have at least two faces with an angle between them. A triangular glass prism has two triangular bases and three rectangular lateral surfaces. These surfaces are inclined to each other. The angle between its two lateral faces is called the angle of the prism.

DISPERSION OF WHITE LIGHT BY A GLASS PRISM

When a ray of light enters the prism, it bends towards the normal; because light is entering from a rarer medium to a denser medium. Similarly, when the light emerges from the prism, it follows the laws of refraction of light. Due to the angle of the prism and due to different wavelengths of different components of white light; the emergent ray gets segregated into different colours. Finally, a colourful band of seven colours is obtained. This phenomenon is called dispersion of white light by the prism.

RAINBOW FORMATION

A rainbow is a natural spectrum appearing in the sky after a rain shower. It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop (see below figure). Due to the dispersion of light and internal reflection, different colours reach the observer’s eye.

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TWINKLING OF STARS

Stars emit their own light and they twinkle due to the atmospheric refraction of light. Stars are very far away from the earth. Hence, they are considered as point sources of light. When the light coming from stars enters the earth’s atmosphere, it gets refracted at different levels because of the variation in the air density at different levels of the atmosphere. When the star light refracted by the atmosphere comes more towards us it appears brighter than when it comes less towards us. Therefore, it appears as if the stars are twinkling at night.

ADVANCE SUNRISE AND DELAYED SUNSET

The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset because of atmospheric refraction. By actual sunrise, we mean the actual crossing of the horizon by the Sun. The below figure shows the actual and apparent positions of the Sun with respect to the horizon. The time difference between actual sunset and the apparent sunset is about 2 minutes. The apparent flattening of the Sun’s disc at sunrise and sunset is also due to the same phenomenon.

SCATTERING OF LIGHT

In the air, part of the sunlight is scattered. The small particles (molecules, tiny water droplets and dust particles) scatter photons the more, the shorter their wavelength is. Therefore, in the scattered light, the short wavelengths predominate, the sky appears blue, while direct sunlight is somewhat yellowish, or even reddish when the sun is very low.

TYNDALL EFFECT

The earth’s atmosphere is a heterogeneous mixture of minute particles. These particles include smoke, tiny water droplets, suspended particles of dust and molecules of air. When a beam of light strikes such fine particles, the path of the beam becomes visible. The light reaches us, after being reflected diffusely by these particles. The phenomenon of scattering of light by the colloidal particles gives rise to Tyndall effect. This phenomenon is seen when a fine beam of sunlight enters a smoke-filled room through a small hole. Thus, scattering of light makes the particles visible. Tyndall effect can also be observed when sunlight passes through a canopy of a dense forest.

WHY IS THE COLOUR OF THE CLEAR SKY BLUE?

The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelengths at the blue end than light of longer wavelengths at the red end. The red light has a wavelength about 1.8 times greater than blue light. Thus, when sunlight passes through the atmosphere, the fine particles in air scatter the blue colour (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes. If the earth had no atmosphere, there would not have been any scattering. Then, the sky would have looked dark. The sky appears dark to passengers flying at very high altitudes, as scattering is not prominent at such heights.

Important Questions

1. A man can read the number of a distant bus clearly but he finds difficulty in reading a book. From which defect of the eye is suffering from?

2. What type of spectacles should be worn by a person having the defects of myopia as well as hypermetropia? How does it help?

3. The sun near the horizon appears flattened at the sun set and sun rise. Explain why.

4. Explain why and when the sun is overhead at noon it appears white

5. A boy uses spectacles of focal length -50 cm. Name the defect of vision he is suffering from. Compute the power of this lens.

6. Give the meaning of the term ‚ VIBGYOR‛ with which phenomenon is it connected?

7. Explain the following terms connected with the eye. (i) Ciliary muscles (ii) Accommodation.

8. What is meant by spectrum of white light?

9. What will be colour of the sky in the absence of atmosphere?

10. Why are the traffic light signals (or danger signals) of red colour?

11. Why does the sky appear dark and black to an astronaut instead of blue?

12. Explain why, when the sun is overhead at noon, it appears white?

13. What is Atmospheric Refraction?

14. A person with myopic eye cannot see objects beyond 1.2metre distinctly. What should be the nature of corrective lenses to restore proper vision?

15. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?

16. The far point of myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to enable him to see very distant objects distinctly?

17. The far point of a myopic person is 150 cm in front the eye. Calculate the focal length and power of a lens required to enable him to see distant objects clearly.

18. How is the eye lens held in its position?

19. What is meant by near point?

20. What is meant by least distance of distinct vision?

21. Which part of the eye controls the amount of the light entering the eye?

22. Which liquid fills the space behind the cornea?

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23. Why is blind spot so called?

24. What is meant by the accommodation of the eye?

25. What is the least distance of distinct vision of a normal human eye?

26. Name the defects of vision of human eye?

27. What is the other name of near sightedness?

28. Where is the image formed in an eye suffering from near sightedness?

29. What is the other name of long sightedness?

30. Where is the image formed in an eye suffering from long sightedness?

31. How is long sightedness corrected?

32. A person has to use a concave lens in his spectacles. What defect of vision is he suffering from?

33. What is the other name of Presbyopia?

34. What is the twinkling of stars due to?

35. Give one example of source of white light.

36. Which scientist first explains the dispersion of light?

37. Name the delicate membrane in the eye having enormous number of light sensitive cells.

38. What kind of lens is used in the spectacles of a person suffering from Myopia (near sightedness)?

39. On what factor the colour of the scattered light depends?

40. What is a function of choroids?

41. Why does sky appear blue on a clear sky?

42. What happens to the lens and the ciliary muscles when you are looking at nearby objects?

43. In an experiment the image of a distant object formed by a concave mirror is obtained on a screen. To determine the focal length of the mirror, you need to measure the distance between the:-

(a) Mirror and the screen

(b) Mirror and the object

(d) Mirror and the screen and also between the object and the screen.

Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

Ans: A normal eye is unable to clearly see the objects placed closer than 25 cm because the ciliary muscles of eyes are unable to contract beyond a certain limit. If the object is placed at a distance less than 25 cm from the eye, then the object appears blurred and produces strain in the eyes.

9. What happens to the image distance in the eye when we increase the distance of an object from the eye?

Ans: Since the size of eyes cannot increase or decrease, the image distance remains constant. When we increase the distance of an object from the eye, the image distance in the eye does not change. The increase in the object distance is compensated by the change in the focal length of the eye lens. The focal length of the eyes changes in such a way that the image is always formed at the retina of the eye.

10. Why do stars twinkle?

Ans: Stars emit their own light and they twinkle due to the atmospheric refraction of light. Stars are very far away from the earth. Hence, they are considered as point sources of light. When the light coming from stars enters the earth’s atmosphere, different levels of the atmosphere. When the star light refracted by the atmosphere comes more towards us, it appears brighter than when it comes less towards us. Therefore, it appears as if the stars are twinkling at night.

11. Explain why the planets do not twinkle?

Ans: Planets do not twinkle because they appear larger in size than the stars as they are relatively closer to earth. Planets can be considered as a collection of a large number of point-size sources of light. The different parts of these planets produce either brighter or dimmer effect in such a way that the average of brighter and dimmer effect is zero. Hence, the twinkling effects of the planets are nullified and they do not twinkle.

12. Why does the Sun appear reddish early in the morning?

Ans: During sunrise, the light rays coming from the Sun have to travel a greater distance in the earth’s atmosphere before reaching our eyes. In this journey, the shorter wavelengths of lights are scattered out and only longer wavelengths are able to reach our eyes. Since blue colour has a shorter wavelength and red colour has a longer wavelength, the red colour is able to reach our eyes after the atmospheric scattering of light. Therefore, the Sun appears reddish early in the morning.

13. Why does the sky appear dark instead of blue to an astronaut?

Ans: The sky appears dark instead of blue to an astronaut because there is no atmosphere in the outer space that can scatter the sunlight. As the sunlight is not scattered, no scattered light reach the eyes of the astronauts and the sky appears black to themit gets refracted at different levels because of the variation in the air density at

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