part | Aster Classes

Question 1:

Match the pairs.

Group ‘A’Group ‘B’
a. C2H61. Unsaturated hydrocarbon
b. C2H22. Molecular formula of an alcohol
c. CH4O3. Saturated hydrocarbon
d. C3H64. Triple bond
ANSWER:
Group ‘A’Group ‘B’
a. C2H61. Saturated hydrocarbon
b. C2H22. Triple bond
c. CH4O3. Molecular formula of an alcohol
d. C3H64. Unsaturated hydrocarbon 
Question 2:
Draw an electron dot structure of the following molecules. (Without showing the circles)

a. Methane

b. Ethene

c. Methanol

d. Water

ANSWER:

Question 3:
Draw all possible structural formulae of compounds from their molecular formula given below.
a. C3H8  
b. C4H10  
c. C3H
ANSWER:
Question 4:
Explain the following terms with example.

a. Structural isomerism

b. Covalent bond

c. Hetero atom in a carbon compound

d. Functional group

e. Alkane

f. Unsaturated hydrocarbon

g. Homopolymer

h. Monomer

i. Reduction

j. Oxidant

a. Structural isomerism: -Structural isomerism or constitutional isomerism is a form of isomerism in which molecules have same molecular formula but different arrangements of the atoms in space.

Different arrangement may be in bonding patterns and atomic organization.

For example: CH3OCH3 and CH3CH2OH are structural isomers.

b. Covalent bond: -Covalent bond is a chemical bond that involves the sharing of electron pairs between atoms.

These electron pairs are known as shared pairs or bonding pairs.

It is also known as molecular bond.

For example: Molecules that have covalent linkages are hydrogen, nitrogen, chlorine, water, and ammonia (H2, N2, Cl2, H2O, NH3).

A single line indicates a single bond between two atoms (i.e.involving one electron pair), double lines (=) indicate a double bond between two atoms (i.e. involving two electron pairs), and triple lines (≡) represent a triple bond (C≡O).


c. Hetero atom in a carbon compound: It is a compound formed by replacement of carbon and hydrogen by heteroatom in a compound.

A heteroatom is any atom other than carbon or hydrogen.

Typical heteroatoms are nitrogen, oxygen, sulfur, phosphorus, chlorine, bromine, and iodine.

Similarly, Nitrogen is the hetero atom in Ethyl amine ( CH3-CH2NH2


d. Functional group: The functional group is defined as an atom or group of atoms joined in a specific manner, which gives the chemical properties of the organic compound and they are the centers for chemical reactivity.

Compounds having a similar functional group undergoes similar reactions.

For example:


1. Alkane: The functional group presence in the alkane is -C-C-. The IUPAC group suffix of an alkane is –ane.

Example: Methane CH4


2. Alkene: The functional group presence in the alkene is -C=C- (double bond). The IUPAC group suffix of an alkene is –ene.

Example: butane


3. Alkynes: The functional group presence in the alkyne is -C ≡ C- (triple bond). The IUPAC group suffix of an alkyne is –yne.

Example: Propyne

4. Arenes: They contain a benzene ring as the functional group.

Example: Benzene


5. Halides: The functional group presence in halides is X(halogen).

Example: Chloromethane


6. Alcohols: The functional group, which is present in alcohol, is -OH. The IUPAC group suffix of alcohol is –ol.

Example: Ethanol

7. Aldehydes: The functional group, which is present in an aldehyde, is -CHO. The IUPAC group suffix of an aldehyde is –al.

Example: Formaldehyde

8. Ketones: The functional group, which is present in a ketone is >C=O. The IUPAC group suffix of a ketone is –one.
Example: Acetone

9. Carboxylic acid: The functional group present in a carboxylic acid is -COOH. The IUPAC group suffix of a carboxylic acid is –oic acid.

Example: Acetic acid

10. Amine: The functional groups present in an amine are -NH2>NH>N- The IUPAC group prefix of an amine is amino– or the suffix is –amine.
Example: Methylamine

11. Ester: The functional group present in an ester is -COOR The IUPAC group suffix of an ester is –ate.
Example: Ethyl acetate

e. Alkane: Alkane is a saturated hydrocarbon.

It is formed when there is sharing of one electron pair between carbon atoms in a compound.

The general formula for alkane is CNH2N+2, where N is equal to no of carbon atoms in a compound.

For example:

C2H6Ethane
C3H8propane
C4H10butane
C5H12pentane
C6H14hexane
C7H16heptane
C8H18octane
C9H20nonane
C10H22decane
C11H24undecane

f. Unsaturated hydrocarbon: An unsaturated hydrocarbon is a hydrocarbon containing at least one double or triple bond.

For example: Alkenes – These unsaturated hydrocarbons are molecules that contain at least one carbon-to-carbon double bond.

With the chemical formula consisting of CnH2n.

The simplest alkene is ethylene.

Alkynes – These unsaturated hydrocarbons are molecules that contain at least one carbon-to-carbon triple bond. 

Acetylenes are common examples of alkynes.

g. Homopolymer: A homopolymer is a polymer formed from the same type of monomer units.

For examples:

Polyvinylchloride (PVC),

Polyethylene,

Polystyrene are homopolymer.

h. Monomer: A monomer is a molecule that forms the basic unit for polymers.
They may be considered as building blocks from which proteins are made.
Monomers may bind to other monomer unit to form a repeating chain molecule.
Monomers may be either natural or synthetic in origin.

For example:

Ethylene,

vinyl chloride,

styrene etc.

i. Reduction: The addition of hydrogen to a substance is called reduction.
The removal of oxygen from a substance is called reduction.
For example:2Ag2O → 4 Ag + O2
In a reaction, silver oxide is changing to silver.
That is, oxygen is being removed from silver oxide.
Removal of oxygen from a substance is called reduction, so silver oxide undergoes reduction.
NiO + H2 → Ni + H2O
In a reaction, Nickel oxide is changing to nickel.
That is, oxygen is being removed from nickel oxide.
Removal of oxygen from a substance is called reduction, so nickel oxide undergoes reduction.
In a reaction, hydrogen is changing to H2O.
That is, oxygen is being added to hydrogen.
Addition of oxygen to a substance is called oxidation, so hydrogen undergoes oxidation.

j. Oxidant:The substance which gives oxygen for oxidation is called an oxidizing agent or oxidant.
The substance which removes hydrogen is called an oxidizing agent or oxidant.

For example:
CuO + H2 → Cu +  H2O Oxidising agent=CuO Reducing agent= H2 Substance oxidised=H2Substance reduced=CuO
ANSWER:
Question 5:
Write the IUPAC names of the following structural formulae.
a. CH3-CH2-CH2-CH3b. CH3-CH2-CH2-CH3
c. CH3-CHOH-CH3d. CH3-CHOH-CH3
e. CH3-CH2-COOHf. CH3-CH2-COOH
ANSWER:

a. CH3-CH2-CH2-CH3 = Butane
b. CH3-CH(OH)-CH3 = Propan-2-ol
c. CH3-CH2-COOH = Propanoic acid
d. CH3-CH2-NH2 = Ethan-1-amine
e. CH3-CHO = Ethanal
f. CH3-CO-CH2-CH3 = Butanone

Question 6:
Identify the type of the following reaction of carbon compounds.

a. CH3 -CH2 -CH2-OH → CH3 -CH2 -COOH

b. CH3 -CH2 -CH3 → 3CO2 + 4H2O

c. CH3 -CH = CH -CH3 + Br2 → CH3 -CHBr – CHBr -CH3

d. CH3 -CH3 + Cl2 → CH3 -CH2 -Cl + HCl

e. CH3 -CH2 -CH2 -CH2 -OH → CH3 -CH2 -CH=CH2 + H2O

f. CH3 -CH2 -COOH + NaOH → CH3 -CH2 -COO – Na+ + H2O

g. CH3 -COOH + CH3 -OH → CH3 -COO- CH3 + H2O

ANSWER:

a. CH3 -CH2 -CH2-OH → CH3 -CH2 -COOH = Oxidation reaction(acidic KMnO4)

b. CH3 -CH2 -CH3 → 3 CO2 + 4H2O = Combustion reaction

d. CH3 -CH3 + Cl2 → CH3 -CH2 -Cl + HCl = Substitution reaction

e. CH3 -CH2 -CH2 -CH2 -OH → CH3 -CH2 -CH=CH2 + H2O = Dehydration reaction

f. CH3 -CH2 -COOH + NaOH → CH3 -CH2 -COO – Na+ + H2O = Neutralization reaction(reaction with base)

g. CH3 -COOH + CH3 -OH → CH3 -COO- CH3 + H2O = Esterification reaction

Question 7:

Write structural formulae for the following IUPAC names.

a. pent-2-oneb. 2-chlorobutane
c. propan- 2 old. methanal
e. butanoic acidf. 1-bromopropane
g. ethanamineh. butanone

ANSWER:


Question 8:
Write answers as directed.
a. What causes the existence of very large number of carbon compound ?
b. Saturated hydrocarbons are classified into three types. Write these names giving one example each.
c. Give any four functional groups containing oxygen as the heteroatom in it. Write name and structural formula of one example each.
d. Give names of three functional groups containing three different hetero atoms. Write name and structural formula of one example each.
e. Give names of three natural polymers. Write the place of their occurrence and names of monomers from which they are formed.
f. What is meant by vinegar and gasohol? What are their uses ?
g. What is a catalyst ? Write any one reaction which is brought about by the use of catalyst ?
ANSWER:

a. Organic compounds mean carbon compounds.

Carbon is unique element in the periodic table.

It has 4 valence electrons.

That means each individual carbon atom can bind to 4 other atoms of almost any variety and each of those 4 can bind to 4 other atoms.

This leads to the formation of organic compounds having incredible variety and complexity – short chains, long chains, ring structures, branched structures and so on.

This self linking property of carbon atom is called catenation, which leads to the existence of a very large number of carbon compounds.


b. Saturated hydrocarbons are classified into three types:
Saturated hydrocarbonExampleStructure
1) Straight chain hydrocarbonsPropane C3H8
2)Branched chain hydrocarbonisobutane C4H10
3)Cyclic hydrocarbonCyclohexane C6H12
c. Four functional groups containing oxygen as the heteroatom in it are as follows:


1. Alcohols: The functional group, which is present in alcohol, is -OH. The IUPAC group suffix of alcohol is –ol. Example: Ethanol

2. Aldehydes: The functional group, which is present in an aldehyde, is -CHO. The IUPAC group suffix of an aldehyde is –al. Example: Formaldehyde

3. Ketones: The functional group, which is present in a ketone is >C=O. The IUPAC group suffix of a ketone is –one. Example: Acetone

4. Carboxylic acid: The functional group present in a carboxylic acid is -COOH. The IUPAC group suffix of a carboxylic acid is –oic acid. Example: Acetic acid

d. Three functional groups containing three different hetero atoms are as follows: Carboxylic acid:

The functional group present in a carboxylic acid is -COOH.

The IUPAC group suffix of a carboxylic acid is –oic acid.

Here, heteroatom is oxygen.


Example: Acetic acid

Amine: The functional groups present in an amine are -NH2>NH>N- The IUPAC group prefix of an amine is amino– or the suffix is –amine. Here, heteroatom is nitrogen.
Example: Methylamine

Halo: The functional group presence in halides is X (halogen= F,Cl,Br,I). Here, heteroatom is chloride. Example: Chloromethane.

e. Give names of three natural polymers. Write the place of their occurrence and names of monomers from which they are formed.
ANSWER:
Natural polymers     Monomer unitOccurrence
1.PolysaccarideGlucose  Starch
2.Cellulose   Glucose     Wood (cell wall of plant cells)
3.Proteins      Alpha aminoacids   Muscles, hair, Skin, Egg
4.D.N.A       Nucleotide(base-deoxyribose-phosphate) Chromosomes of animals
5.R.N.A      Nucleotide(base-ribose-phosphate )   Chromosomes of plants
6.Rubber    Isoprene(CH2=C(CH3)-CH=CH2 )   Latex of rubber tree

f. Vinegar is the type of liquid which consist of acetic acid ( Ethanoic acid ). It is basically produced by the process of fermentation of ethanol through ethanoic acid in the presence of bacteria


Reaction involved in the formation of Vinegar:

CH₃CH₂OH + O₂→ CH₃COOH + H₂O Fermentation is the process of converting sugar into alcohol.

But if the cork of the bottle open for sometimes then there is the second type of fermentation happened. 

In this process, alcohol is changes into acetic acid, so the main compound which formed is vinegar.

Uses of Vinegar are:

It is used in the preparation of the food .

It is used in pickling.
It is used as folk medicine material.
It is used as a household cleaning agent.
Gasohol is a mixture of 90% gasoline and 10% of anhydrous Alcohol (Ethyl Alcohol).
It is commonly known as the alternative fuel or a motor fuel.

Benefits of gasohol are :-

It is cheaper.
It is eco-friendly.
It has higher performance.
It is used as a cleaner to the environment.
It doesn’t freeze in typical conditions.

Uses of gasohol are:

It is used in a fuel or petroleum Industry.
It is used in an automobile industry.
It is used as common gasoline or hydrous around the world.
It is used as a flexible fuel vehicle, because it does not freeze in typical conditions.

g. Catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
For example:
E.g.Name of processEquations (in words or formulae)Catalyst
1Fermentation of glucose to form ethanolGlucose → Ethanol + Carbon dioxideSpecific enzymes (in yeast)
2Hydration of ethene to form ethanolEthene + Water (Steam) Heat → EthanolPhosphoric Acid
3Hydrogenation of unsaturated fats(to harden oils in the manufacture of margarine)Hydrogen + Unsaturated Fats → Saturated Fats
Nickel (Ni)
4Haber’s processNitrogen +Hydrogen → AmmoniaIron

Question 1:

Write names.

a. Alloy of sodium with mercury.

b. Molecular formula of the common ore of aluminium.

c. The oxide that forms salt and water by reacting with both acid and base.

d. The device used for grinding an ore.

e. The nonmetal having electrical conductivity.

f. The reagent that dissolves noble metals.

ANSWER:

a. Sodium amalgam, commonly denoted as Na(Hg), it is an alloy of mercury and sodium.

b. Bauxite(Al2O3.2H2O) is the common ore of aluminium.

c. Metal oxides which react with both acids as well as bases to produce salts and water are also known as amphoteric oxides. For example: Al2O3 is an amphoteric oxide. An amphoteric compound is a molecule or ion that can react both an acid as well as a base to produce salt and water.

d. The device used for grinding an ore is grinding mill.

e. Graphite an allotrope of carbon is a good conductor of electricity.

f. Aqua Regia is 1:3 mixture of concentrated nitric and hydrochloric acids. It dissolves noble metals such as gold, palladium, and platinum.

Question 2:

Substance  Property 
a. Potassium bromide1. Combustible
b. Gold2. Soluble in water
c. Sulphur3. No chemical reaction
d. Neon4. High ductility.

ANSWER:

Substance  Property 
a. Potassium bromideSoluble in water
b. GoldHigh ductility.
c. SulphurCombustible
d. NeonNo chemical reaction


Question 3:

Identify the pairs of metals and their ores from the following.

ANSWER:

Group AGroup B
a. Bauxitei. Aluminium
b. Cassiteriteii. Tin
c. Cinnabariii. Mercury

Question 4:

Explain the terms.

a. Metallurgy

b. Ores

c. Minerals

d. Gangue

ANSWER:

a. Metallurgy: The various processes involved in the extraction of metals from its ores and refining is called metallurgy.

The major steps involved for the extraction of a metal from its ore are:

(i) Concentration of ores (or enrichment of ore)

(ii) Conversion of concentrated ore into metal

(iii) Refining (purification) of impure metal

b. Ores: Those minerals from which metals can be extracted conveniently and profitably.

c. Minerals:” A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes” (Nickel, E. H., 1995).


 “Minerals are naturally-occurring inorganic substances with a definite and predictable chemical composition and physical properties.” (O’ Donoghue,1990).


 “A mineral is a naturally occurring homogeneous solid, inorganically formed, with a definite chemical composition and an ordered atomic arrangement” (Mason, et al,1968).


 “These… minerals …can be distinguished from one another by individual characteristics that arise directly from the kinds of atoms they contain and the arrangements these atoms make inside them” (Sinkankas, 1966).


 “A mineral is a body produced by the processes of inorganic nature, having usually a definite chemical composition and, if formed under favorable conditions, a certain characteristic atomic structure which is expressed in its crystalline form and other physical properties” (Dana & Ford,1932).


 “Every distinct chemical k occurring in inorganic nature, having a definite molecular structure or system of crystallization and well-defined physical properties, constitutes a mineral species” (Brush & Penfield


d. Gangue: – is the unwanted impurities like rock material, dust, soil, sand, earthy particles, limestone, mica etc. present in an ore.

Question 5:

Write scientific reasons.

a. Lemon or tamarind is used for cleaning copper vessels turned greenish.
b. Generally the ionic compounds have high melting points.
c. Sodium is always kept in kerosene.
d. Pine oil is used in froth flotation.
e. Anodes need to be replaced from time to time during the electrolysis of alumina.

ANSWER:


a. Copper vessels turned greenish due to the formation of copper carbonate layer.
The citric acid present in the lemon or tamarind neutralizes the basic copper carbonate and dissolves the layer.
That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.

b. In an ionic compound there is strong electrostatic force of attraction between oppositely charged ions.
To overcome these forces a considerable amount of energy is needed.
Therefore, ionic compounds have high melting points.

c. Sodium is a very reactive metal. It is kept in kerosene to prevent it from coming in contact with oxygen and moisture.
If this happens, it will react with the moisture present in air and form sodium hydroxide.
This is a strongly exothermic reaction and lot of heat is generated.

d. Pine oil is added in the froth flotation method to create froth or bubble so that metal can be purify easily because pine oil prevents the ore from gangue for further mixing.
Pine oil also acts as the best substance for forming froth for the minerals.
It also increases the non wettability of mineral particles.

e. In the electrolysis of alumina, graphite rod is used as anode.
During the electrolytic reduction of alumina, aluminium is produced at the cathode and oxygen gas is evolved at the anode.
This gas reacts with the graphite rods (anode) and forms carbon dioxide.
Thus, the graphite rods are continuously eroded.
Hence, the graphite rods i.e. anodes be replaced from time to time during the electrolysis of fused alumina. 

Question 6:

When a copper coin is dipped in silver nitrate solution, a glitter appears on the coin after some time. Why does this happen? Write the chemical equation.

ANSWER:


Copper is more reactive than silver. Hence, displacement reaction occurs.
When copper coin is dipped in silver nitrate solution, it forms copper nitrate and silver metal.
A shining white deposit of silver metal is formed on copper coin.
The grey solid crystal(glitters) of Ag metal appears on the copper coin and solution turns blue in colour.
Balanced equation: 
2AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2Ag(s)

Question 7:

The electronic configuration of metal ‘A’ is 2,8,1 and that of metal ‘B’ is 2,8,2. Which of the two metals is more reactive? Write their reaction with dilute hydrochloric acid.

ANSWER:


On moving from left to right in a period of periodic table, the chemical reactivity of elements first decreases from sodium to silicon and then increases from phosphorus to chlorine.
The electronic configuration of metal ‘A’ is 2,8,1. This is electronic configuration of sodium metal.
The electronic configuration of metal ‘B’ is 2,8,2.
This is electronic configuration of magnesium metal.
In the first element of third period, sodium, there is 1 valence electron which it can lose easily to react with other substances, so it is very reactive metal.
The second element magnesium has 2 valence electrons.
It is not easy for an atom to lose 2 electrons, so magnesium is less reactive than sodium.
Reaction with dil hydrochloric acid:

Question 8:

Draw a neat labelled diagram.

a. Magnetic separation method.

ANSWER:

b. Froth floatation method.

ANSWER:

c. Electrolytic reduction of alumina.

ANSWER:

d. Hydraulic separation method.

ANSWER:

Question 9:

Write the chemical equation for the following events.

a. Aluminium came in contact with air.

b. Iron filings are dropped in aqueous solution of copper sulphate.

c. A reaction was brought about between ferric oxide and Aluminium.

d. Electrolysis of alumina is done.

e. Zinc oxide is dissolved in dilute hydrochloric acid.

ANSWER:

a. Aluminium came in contact with air.

Aluminum is a very reactive metal.

The outer surface of the metal is actually covered by a very thin layer of the oxide which keeps the metal protected from the air.

But when the oxide layer is damaged, aluminum comes in contact with the air.

It is easily attacked by air.

Then aluminium starts reacting with the oxygen.

It will burn as bright white flame to change into aluminum(III) oxide.

Chemical Equation: 

  

b. Iron filings are dropped in aqueous solution of copper sulphate.

Iron is more reactive than copper.

It can displace Copper (Cu) from its salt Copper sulphate (CuSO4) and its colour changes from blue to green.

Chemical Equation: 

c. A reaction was brought about between ferric oxide and aluminium.

Aluminium is more reactive than iron.

Aluminium metal replaces iron from ferric oxide to form aluminium oxide and iron

Chemical Equation:

d. Electrolysis of alumina is done.

The electrolysis of alumina is carried out in a steel tank lined inside with graphite.

The graphite lining serves as cathode.

Anode is also made up of graphite rods hanging in the molten mass.

The electrolyte consists of alumina dissolved in fused Cryolite(Na3AlF6) and Fluorspar(CaF2).

Cryolite lowers the melting point of alumina and fluorspar increases the fluidity of the mass so that the liberated aluminum metal may sink at the bottom of the cell.

When electric current is passed through this mixture, the aluminum is collected at the cathode in molten state and sinks at the bottom.

e. Zinc oxide is dissolved in dilute hydrochloric acid.

Zinc Oxide is an inorganic compound with the formula ZnO.

It is insoluble in water.

When Zinc oxide reacts with hydrochloric acid it forms zinc chloride and water.

It also leads in the formation of small bubbles of hydrogen.

This is a double displacement reaction.

Chemical Equation: 

Question 10:

Complete the following statement using every given options.

During the extraction of aluminium…………..

a. Ingredients and gangue in bauxite.

b. Use of leaching during the concentration of ore.

c. Chemical reaction of transformation of bauxite into alumina by Hall’s process.

d. Heating the aluminium ore with concentrated caustic soda.

ANSWER:

a. Bauxite is the main ore of aluminium.

Silica (SiO2), ferric oxide (Fe2O3) and titanium oxide (TiO2) are the impurities present in bauxite.

Ingredient in bauxite are molten cryolite (Na3AIF6), fluorspar (CaF2).


b. The separation of impurities(silica (SiO2), ferric oxide (Fe2O3) and titanium oxide (TiO2)) in bauxite ore is done by leaching process using either Bayer’s method or Hall’s method.


c. In the Hall’s process the bauxite is in powdered form and then leached by heating with aqueous sodium carbonate in the digester to form water soluble sodium aluminate.

Then the insoluble impurities are filtered out.

The filtrate is warmed and neutralised by passing carbon dioxide gas through it.

This results in the precipitation of aluminium hydroxide.

The precipitate of Al(OH)3 obtained in both, Bayer’s and Hall’s processes is filtered, washed, dried and then calcined by heating at 10000C to obtain alumina.

d. When Aluminium ore is heated with caustic soda  (NaOH) solution under high pressure for 2-8 hours at 1400-1500C, water soluble sodium aluminate is formed.

Question 11:

Divide the metals Cu, Zn, Ca, Mg, Fe, Na, Li into three groups, namely reactive metals, moderately reactive metals and less reactive metals.

ANSWER:

Highly reactive metals
moderately reactive metalsless reactive metals.
CaFeAu
MgZnAg
NaCuPt
Li

Question 1:

Match the columns in the following table and explain them.
Column 1–Column 2—Column 3

answer:

Column 1Column 2Column 3
Farsightedness

Far away object can be seen clearlyConvex lens
Presbyopia

Problem of old ageBifocal lens
Nearsightedness

Nearby object can be seen clearly Concave lens

Farsightedness

Hypermetropia

This defect is also known as Hypermetropia. It is an eye defect in which a person is unable to see nearby objects clearly but can see the far away objects clearly.

It is caused due to

1. reduction in the curvature of the lens
2. decrease in the size of the eyeball
Since a convex lens has the ability to converge incoming rays, it can be used to correct this defect of vision, as you already have seen in the animation.


Nearsightedness:

Myopia

This defect is also known as Myopia.
It is a defect of vision in which a person clearly sees all the nearby objects, but is unable to see distant objects comfortably and his eye is known as a myopic eye.
A myopic eye has its far point nearer than infinity.
It forms the image of a distant object in front of the retina as shown in the figure.

It is caused by

1. increase in curvature of the lens
2. increase in length of the eyeball.
Since a concave lens has an ability to diverge incoming rays, it is used to correct this defect of vision. The image is allowed to form at the retina by using a concave lens of suitable power.

Presbyopia

Presbyopia: This is a common defect of vision, which generally occurs at old age.
A person suffering from this type of defect of vision cannot see nearby objects clearly and distinctly.
A presbyopic eye has its near point greater than 25 cm and it gradually increases as the eye becomes older.

Presbyopia is caused by the1. weakening of the ciliary muscles2. reduction in the flexibility of the eye lensIt can be corrected using bifocal lens.


Question 2:

Draw a figure explaining various terms related to a lens.

ANSWER:

Terms Associated with Lenses:

Optical centre:-
Optical centre is a point at the centre of the lens. It always lies inside the lens and not on the surface. It is denoted by ‘O’.

Centre of curvature:-
It is the centre point of arcs of the two spheres from which the given spherical lens (concave or convex) is made. Since a lens constitutes two spherical surfaces, it has two centers of curvature.

Radius of curvature:
The distance of the optical centre from either of the centres of curvatures is termed as the radius of curvature.

Principal axis:
The imaginary straight line joining the two centers of curvature and the optical centre (O) is called the principal axis of the lens.
Focus:
The focus (F) is the point on the principal axis of a lens where all incident parallel rays after refraction from the lens meet or appear to diverge from. For lenses there are two foci (F1 and F2) depending on the direction of incident rays.

Focal length:
The distance between the focus (F1 or F2) and the optical centre (O) is known as the focal length of the lens.    

Question 3:

At which position will you keep an object in front of a convex lens so as to get a real image of the same size as the object? Draw a figure.

Answer:

When an object is placed at the centre of curvature 2F1 of a convex lens, we will get a real image of the same size as the object.

Question 4:

Give scientific reasons:

a. Simple microscope is used for watch repairs.

ANSWER:

Simple microscope has convex lens which has the ability to produce 20 times larger as well as erect image of an object. This means the magnifying power of the microscope is very high. Thus, simple microscopes are used by watchmakers to see the small parts and screws of the watch while repairing it.

b. One can sense colours only in bright light.

ANSWER:

The cells present on the retina and responsible for colour vision are known as cone cells.
These cells become active only under bright light and remain inactive under dark.
Thus, we are able to sense only in bright light.


c. We cannot clearly see an object kept at a distance less than 25 cm from the eye.

ANSWER:

We cannot clearly see an object kept at a distance less than 25 cm from the eye.
This is because the ciliary muscles of our eyes are unable to contract beyond certain limit.
If the object is placed at a distance less than 25 cm from the eye, then the object appears blurred because light rays coming from the object meet behind the retina.

Question 5:

Explain the workings of an astronomical telescope using refraction of light.

ANSWER:

The astronomical telescope consists of two lenses: objective and eyepiece.
Objective has larger focal length and diameter to accommodate the maximum amount of light coming from the far away (astronomical) objects.
A parallel beam of rays from an astronomical object is made to fall on the objective lens of the telescope.
It forms a real, inverted and diminished image A’B’ of the object.
The eyepiece is so adjusted that A’B’ lies just at the focus of the eye piece.
Therefore, a highly magnified image of the object is formed at infinity.
The same has been shown in the figure below.

Question 6:

Distinguish between:

a. Farsightedness and Nearsightedness
b. Concave lens and Convex lens
ANSWER:

a.


b.

Question 7:

What is the function of the iris and the muscles connected to the lens in human eye?

ANSWER:

Function of Iris:

The iris is a muscular diaphragm that controls the size of the pupil, which, in turn, controls the amount of light entering the eye. It also gives colour to the eye.

Function of ciliary muscles:

The eye lens is held in position by the ciliary muscles. The focal length of the eye lens is adjusted by the expansion and contraction of the ciliary muscles.

Question 8:

Solve the following examples.

i. Doctor has prescribed a lens having power +1.5 D. What will be the focal length of the lens? What is the type of the lens and what must be the defect of vision?

ANSWER:

ii. 5 cm high object is placed at a distance of 25 cm from a converging lens of focal length of 10 cm. Determine the position, size and type of the image. 

ANSWER:

iii. Three lenses having power 2, 2.5 and 1.7 D are kept touching in a row. What is the total power of the lens combination? 

ANSWER:

iv. An object kept 60 cm from a lens gives a virtual image 20 cm in front of the lens. What is the focal length of the lens? Is it a converging lens or diverging lens?

ANSWER:


Question 1:

Fill in the blanks and rewrite the sentence.

a. The amount of water vapour in air is determined in terms of its ……….. .

b. If objects of equal masses are given equal heat, their final temperature will be different. This is due to difference in their …………….. .

c. During transformation of liquid phase to solid phase, the latent heat is ………… .

ANSWER:

a. The amount of water vapour in air is determined in terms of its absolute humidity.
b. If objects of equal masses are given equal heat, their final temperature will be different. This is due to differences in their different specific heat capacity.
c. During transformation of liquid phase to solid phase, the latent heat is latent heat of fusion.

Question 2:

Observe the following graph. Considering the change in volume of water as its temperature is raised from 0°C, discuss the difference in the behaviour of water and other substances. What is this behaviour of water called?

ANSWER:

Most of the substances expand on heating and contract on cooling. Whereas, from the graph, it is clearly visible that water shows a distinct and peculiar behavior between 0oC to 4oC.
Water, instead of expanding, contracts between 0oC to 4oC. After 4oC, it shows the normal behavior of expansion as is shown by other substances.
Thus, at 4oC, water posses maximum density and minimum volume. 
This behavior of water between 0oC to 4oC is known as anomalous behavior of water.

Question 3:

What is meant by specific heat capacity? How will you prove experimentally that different substances have different specific heat capacities?

Take three balls of iron, copper and lead of equal mass and put them in boiling water for some time.
Then, take them out of the water and measure their temperature.
All of them will be at temperature 100oC. Now, put them immediately on the thick slab of wax.
Note the depth that each of the ball goes into the wax.
The ball which absorbs more heat from the water will give more heat to wax.
More wax will thus melt and the ball will go deeper in the wax. It will be observed that the iron ball goes deepest into the wax.
Lead ball goes the least and copper ball goes to intermediate depth.
This shows that for equal rise in temperature, the three balls have absorbed different amounts of heat.
This means that the property which determines the amount of heat absorbed by a ball is different for the three balls.
This property is called the specific heat capacity.

Question 4:

While deciding the unit for heat, which temperature interval is chosen? Why?

ANSWER:

While deciding the unit for heat (which is calorie), the temperature interval chosen is 14.5oC-15.5oC.
We know that the amount of heat released or absorbed by a body is given as∆Q =ms ∆T
Now, we also know that one calorie is defined as the amount of heat required to raise the temperature of 1 g of water through 1oC.
Thus, for 1 calorie of heat energy, the specific heat capacity of water should be 1 cal g-1 oC-1.
It is found experimentally that the specific heat capacity of water is 1 cal g-1 oC-1 when the temperature range is 14.5oC-15.5oC.

Question 5:

Explain the following temperature vs time graph.

ANSWER:

In the given graph, line AB represents conversion of ice into water at constant temperature.
When ice is heated, it melts at 0oC and converts into water maintaining constant temperature of 0oC.
This constant temperature, at which the ice converts into water is called the melting point of ice.
Also, during this transition, the ice absorbs heat energy.
This heat energy is utilized for weakening the bonds between the atoms or molecules in the ice to transform itself into liquid.
This heat energy absorbed by ice, at constant temperature, to convert it into liquid is called the latent heat of fusion.
Once all the ice is transformed into water, the temperature of the water starts rising. It increases upto 100oC.
Line BC in the graph represents rise in temperature of water from 0oC to 100oC.
Thereafter, even though heat energy is supplied to water, its temperature does not rise.
The heat energy is absorbed by water at this temperature and is used to break the bonds between molecules of the liquid and convert the liquid into gaseous state.
Thus, during transformation from liquid phase to gas phase, heat energy is absorbed by the liquid, but its temperature does not change.
The constant temperature at which the liquid transforms into gaseous state is called the boiling point of the liquid.
The heat energy absorbed at constant temperature during transformation of liquid into gas is called the latent heat of vaporization.

Question 6:

Explain the following:

a. What is the role of anomalous behaviour of water in preserving aquatic life in regions of cold climate?

ANSWER:

The anomalous behaviour of water is that it contracts from 0oC to 4oC and beyond 4oC it expands.
Thus, the density of water is maximum at 4oC.
When the surrounding temperature falls, the water in oceans and rivers cools down and say the temperature of water reaches 4oC.
Thus, the water reaches its maximum density at this temperature. 
Below this temperature (4oC), the water layer on the surface expands due to anomalous behaviour of water because of which its density decreases.
Thus, this colder layer remains on top  and converts into ice which acts as an insulator and does not allow the temperature of water layer below it to fall below 4oC.
In this way, a livable temperature is maintained for the aquatic life under the oceans and rivers due to the anomalous behaviour of water.
b. How can you relate the formation of water droplets on the outer surface of a bottle taken out of refrigerator with formation of dew?

ANSWER:

In both the given processes, the temperature of the air near the surface of bottle or the leaves (in case of dew formation) decreases to dew point.
Thus, the air becomes saturated with water vapour.
As a result, water vapour converts or condenses into tiny water droplets which appears on the surface of bottle or leaves.

c. In cold regions in winter, the rocks crack due to anomalous expansion of water.

ANSWER:

Water has the property of expanding below 4oC.
Thus, in cold regions when the temperature falls below 4oC, the water content present in rocks expands.
Due to this expansion of water or increase in volume of water, the rocks cracks.

Question 7:

Answer the following:

a. What is meant by latent heat? How will the state of matter transform if latent heat is given off?

ANSWER:

Latent heat of a body is the amount of heat required to change the state of unit mass of the body from solid to liquid or from liquid to gas without any change in temperature.
If latent heat is given off, then the body in liquid state will transform to solid state and the body in vapour state will transform to liquid state.

This means the internal energy of the matter decreases when latent heat is given off.

b Which principle is used to measure the specific heat capacity of a substance?

ANSWER:

Principle of heat exchange is used in the calorimetry method to determine the specific heat capacity of a substance.
c. Explain the role of latent heat in the change of state of a substance?

ANSWER:

According to the kinetic model, the total energy of a molecule is the sum of kinetic energy due to its motion (which depends on temperature) and its potential energy (which depends on the force of attraction between the molecules and the separation between them.
During the phase change of a substance, its temperature does not increase and hence its kinetic energy.
But the potential energy increases or decreases depending on the type of phase transformation (for example, while melting of ice, the separation between the molecules of ice increases and hence its potential energy). 
Thus, some energy is required in increases or decreasing the separation between the molecules.
Thus, the heat supplied during phase transformation is used up in increasing or decreasing the potential energy and this heat energy is known as latent heat.
d. On what basis and how will you determine whether air is saturated with vapour or not?

ANSWER:

On the basis of amount of water vapour present in the air, it can be either saturated or unsaturated.
If the amount of water vapours exceeds the amount that the air can contain, then it is called saturated.
If the amount of water vapour is less than the limit of the amount that air can contain then it is called unsaturated.
We can determine whether the air is saturated with vapour or not in terms of relative humidity.
If the relative humidity is 100%, the air will be saturated otherwise not.

Question 8:

Read the following paragraph and answer the questions.

If heat is exchanged between a hot and cold object, the temperature of the cold object goes on increasing due to gain of energy and the temperature of the hot object goes on decreasing due to loss of energy.
The change in temperature continues till the temperatures of both the objects attain the same value. In this process, the cold object gains heat energy and the hot object loses heat energy.
If the system of both the objects is isolated from the environment by keeping it inside a heat resistant box (meaning that the energy exchange takes place between the two objects only), then no energy can flow from inside the box or come into the box.
i. Heat is transferred from where to where?
ii. Which principle do we learn about from this process?iii. How will you state the principle briefly?
iv. Which property of the substance is measured using this principle?

ANSWER:

(i) Heat is transferred from the object at higher temperature to the object at lower temperature.
(ii) We learn the principle of heat exchange from this process.
(iii) Principle of heat exchange states that the heat energy lost by hot object is always equal to heat gained by cold object provided that the system of both the objects is isolated.
(iv) Specific heat of an object can be measured using this principle.

Question 9:

Solve the following problems:

a. Equal heat is given to two objects A and B of mass 1 g. Temperature of A increases by 3°C and B by 5°C. Which object has more specific heat? And by what factor?

b. Liquid ammonia is used in ice factory for making ice from water. If water at 20°C is to be converted into 2 kg of ice at 0°C, how many grams of ammonia are to be evaporated? (Given: The latent heat of vaporization of ammonia= 341 cal/g)

c. A thermally insulated pot has 150 g ice at temperature 0°C. How much steam of 100°C has to be mixed to it, so that water of temperature 50°C will be obtained? (Given : latent heat of melting of ice = 80 cal/g, latent heat of vaporization of water = 540 cal/g, specific heat of water = 1 cal/g °C)

d. A calorimeter has mass 100 g and specific heat 0.1 kcal/ kg °C. It contains 250 gm of liquid at 30°C having specific heat of 0.4 kcal/kg °C. If we drop a piece of ice of mass 10 g at 0°C, What will be the temperature of the mixture?

Science Chapter 4 – Effects Of Electric Current

SSC, SCIENCE PART I, NEW SYLLABUS, FOR BOARD EXAM 2020,

Question 1:

Tell the odd one out. Give proper explanation.

a. Fuse wire, bad conductor, rubber gloves, generator.

b. Voltmeter, Ammeter, galvanometer, thermometer.

c. Loud speaker, microphone, electric motor, magnet.

ANSWER:

a. The odd one out is generator. It is an electrical device for producing electricity. Fuse wire, bad conductor and rubber gloves have high resistance and are used for blocking electricity. Thus, they can be used as a safety measure against heavy electricity. 
b. The odd one out is thermometer. It is an instrument for measuring the temperature of a body. Rest of the three are electrical instruments based on the phenomenon of electromagnetism and are used for measuring some electrical parameters such as current and voltage. 
c. The odd one out is magnet. Loud speaker, microphone and electric motor are based on the phenomenon of electromagnetism.

Question 2:

Explain the construction and working of the following. Draw a neat diagram and label it.

a. Electric motor

b. Electric Generator (AC)

ANSWER:

a. Motor principle:

The basic principles on which the electric motor works is the magnetic effect of current. A current carrying rectangular coil starts rotating when placed in a magnetic field. 


Construction: The given figure illustrates the internal parts of a simple electric motor.

A motor consists of a rectangular coil ABCD of insulated copper wire.

The coil is placed between two magnetic poles such that the magnetic field acts normal on lengths AB and CD.

The coil is connected with two carbon brushes at points B1 and B2 respectively.

The inner sides of these carbon brushes are in contact with half rings R1 and R2, which are insulated and in contact with an axle (not shown in the figure).


Working:

When a current is allowed to flow through the coil ABCD by closing the switch, the coil starts rotating anti-clockwise.

This happens because a downward force acts on length B1 B2 and at the same time, an upward force acts on length R1 R2.

As a result, the coil rotates anti-clockwise.
The current in length B1 B2 flows from B1 to B2, and magnetic field acts from left to right normal to length B1 B2.

Hence, according to Fleming’s left hand rule, a downward force acts on length AB.

Similarly, the current in length CD flows from C to D, and magnetic field acts from left to right normal to its length.

Hence, an upward force acts on length R1 R2. These two forces cause the coil B1 B2 R1 R2 and the axle to rotate anti-clockwise.

After half-rotation, the position of length B1 B2 and R1 R2 get interchanged.

Simultaneously, half ring R2 comes in contact with brush B1 and half ring R1 comes in contact with brush B2 respectively.

Hence, the direction of current in coil ABCD gets reversed and flows through DCBA.

An electric device that reverses the direction of current in a circuit is called a commutator.

Thus, the split ring acts as a commutator of the electric motor.

Now, due to the reverse direction of current in lengths AB and CD, an upward force acts on length AB, which pushes it up and a downward force acts on length CD,

which pushes it down. As a result, the coil ABCD further rotates anti-clockwise.

The reversal of the current through the coil ABCD repeats at each half-rotation, while its anti-clockwise rotation continues.

b. Electric Generator principle : An electric generator is a machine that generates electricity by rotating its rotor in a magnetic field. Thus, it converts mechanical energy into electrical energy.

Construction: A generator consists of a rectangular coil MNST of insulated copper wire placed between two strong magnetic poles.

The two ends of the coil MNST are connected with brushes A and B of rings C and D respectively.

The inner sides of the rings are insulated. They are attached with an axle X, which can be rotated mechanically.

Brushes A and B are connected with a galvanometer that can measure the flow of current in coil MNST.

Working: When the axle is rotated, lengths MN and ST move up and down respectively.

Since lengths MN and ST are moving in a magnetic field, a current is induced in these lengths caused by electromagnetic induction.

The direction of the induced current in both the lengths is given by Fleming’s right hand rule.

Since length MN is moving upwards in the magnetic field that acts from left to right, the direction of the induced current will be from M to N.

Similarly, the direction of the induced current in length ST will be from S to T.

Hence, an induced current will set up in the coil in the direction MNST, which produces deflection in the galvanometer.

After half-rotation, length MN starts moving down, whereas length ST starts moving up.

The direction of the induced current in the coil gets reversed i.e., the induced current will now flow from T to M via S and N i.e., TSNM.

Therefore, we can conclude that after each half-rotation, the direction of the induced current is reversed.

This current is called an alternating current (AC). An AC reverses its direction after equal time intervals. 

Question 3:

Electromagnetic induction means-

a. Charging of an electric conductor.

b. Production of magnetic field due to a current flowing through a coil.

c. Generation of a current in a coil due to relative motion between the coil and the magnet.

d. Motion of the coil around the axle in an electric motor.

ANSWER:

Electromagnetic induction means generation of a current in a coil due to relative motion between the coil and the magnet.

Question 4:

Differentiating PropertyAC GeneratorDC Generator
1.DefinitionAC generator is a mechanical device which converts mechanical energy into AC electrical power.DC generator is a mechanical device which converts mechanical energy into DC electrical power.
2Direction of CurrentIn an AC generator, the electrical current reverses direction periodically.In a DC generator, the electrical current flows only in one direction.
3Basic DesignIn an AC generator, the coil through which the current flows is fixed while the magnet moves. The construction is simple and costs are less.In a DC generator, the coil through which the current flows rotates in a fixed field. The overall design is very simple but construction is complex due commutators and slip rings.
4CommutatorsAC generator does not have commutators.DC generators have commutators to make the current flow in one direction only.
5RingsAC generators have slip-rings.DC generators have split-ring commutators.

Question 5:

Which device is used to produce electricity? Describe with a neat diagram.

a. Electric motor

b. Galvanometer

c. Electric Generator (DC)

d. Voltmeter

ANSWER:

The device used for producing electricity is Electric generator (DC). It is based on the phenomenon of electromagnetic induction.

Working:  When the axle is rotated, lengths MN and ST move up and down, respectively.

Since lengths MN and ST are moving in a magnetic field, a current gets induced in these lengths caused by an electromagnetic induction.

The direction of the induced current in both the lengths is given by Fleming’s right hand rule.

In this arrangement, brush A always remains in contact with the length moving up, whereas brush B always remains in contact with the length moving down.

Here, split rings C and D act as a commutator. In this case, the direction of the current induced in the coil will be from M to T via N and S for the first half-rotation, and from T to M via S and N for the second half-rotation of coil MNST.

Hence, we get a unidirectional current called direct current (DC).

Question 6:

How does the short circuit form? What is its effect?

ANSWER:

Short circuit occurs when naked live and neutral wires touch each other.

In such situations, the resistance of the circuit becomes very less. Now, according to Ohm’s law, current is inversely proportional to resistance.

Thus, the decrease in value of resistance of the circuit raises the current to a significant amount.

As a result, the wires become hot and sparks are caused by Joule’s heating effect of current.

Question 7:

Give Scientific reasons.

a. Tungsten metal is used to make a solenoid type coil in an electric bulb.

b. In the electric equipment producing heat e.g. iron, electric heater, boiler, toaster etc, an alloy such as Nichrome is used, not pure metals.

c. For electric power transmission, copper or aluminium wire is used.

d. In practice the unit kWh is used for the measurement of electrical energy, rather than joules.

ANSWER:

a. Tungsten metal is used to make a solenoid type coil in an electric bulb because its melting point is very high. Thus, when a high amount of current is passed through it, it becomes red hot and emit lights without getting burnt.



b. In the electric equipment producing heat, such as iron, electric heater, boiler, toaster etc., an alloy such as Nichrome is used, not pure metals because of the following reasons:

(i) Resistivity of Nichrome is more compared to pure metal.

(ii) Melting point of Nichrome is high as compared to pure metal.

(iii) Nichrome does not get oxidized when heated in air whereas metal does.



c. ​For electric power transmission, Copper or Aluminium wire is used because they provide a low resistance path to the flow of current.

Thus, the power loss in the low resistance transmission wire will be less.



d. In practice, the unit kWh is used for the measurement of electrical energy, rather than joules. This is because the joule is a very small unit and the energy consumption in day to day life is very large i.e.

it comes in figures of 106 to 108. Thus, to reduce the complexity of handling such large figures, a bigger unit was required.

This bigger unit used for the measurement of electrical energy is kWh and is related to joule as1 kWh = 3.6 × 106 J

Hence, the energy reading commercially became simpler by using this bigger unit instead of joule.

Question 8:

Which of the statement given below correctly describes the magnetic field near a long, straight current carrying conductor?

a. The magnetic lines of force are in a plane, perpendicular to the conductor in the form of straight lines.

b. The magnetic lines of force are parallel to the conductor on all the sides of the conductor.

c. The magnetic lines of force are perpendicular to the conductor going radially outward.

d. The magnetic lines of force are in concentric circles with the wire as the center, in a plane perpendicular to the conductor.

ANSWER:

The correct statement describing the magnetic field near a long, straight current carrying conductor is :The magnetic lines of force are in concentric circles with the wire as the center, in a plane perpendicular to the conductor

Question 9:

What is a solenoid? Compare the magnetic field produced by a solenoid with the magnetic field of a bar magnet. Draw neat figures and name various components.

ANSWER:

A solenoid is a long straight insulated wire, such as a copper coil, often wrapped around a cylinder-shaped body. The diameter of the solenoid is lesser than its length. It produces a magnetic field when electric current is passed through it.


Magnetic field produced by a solenoid is shown below:

Magnetic field produced by a bar magnet is shown below:

On comparing field lines produced by a solenoid with that produced by a bar magnet, we observe that they are very much identical. Thus, a solenoid acts as a bar magnet when a current is passed through it.

Question 10:

Name the following diagrams and explain the concept behind them.

ANSWER:

a. It represents Fleming’s right hand rule used for finding the direction of induced current with respect to the directions of the magnetic field and motion of the conductor.

The direction of current induced in a conductor can be obtained by holding the thumb, index finger, and the middle finger of your right hand mutually perpendicular to each other.

In this situation, the thumb indicates the direction of the motion of the conductor, the index finger points along the magnetic field, and the middle finger points along the current induced in the conductor.


b. It represents Fleming’s left hand rule used for finding the direction of magnetic force when a current carrying conductor is placed in a magnetic field.

This rule states that if you stretch the thumb, index finger, and middle finger of your left hand such that they are mutually perpendicular to each other, then your index finger represents the direction of the field, the middle finger represents the direction of the current, and the thumb represents the direction of the force experienced by the conductor.

Question 11:

Identify the figures and explain their use.

ANSWER:

(a) Figure represents a fuse. An electric fuse is a safety device that protects the wiring against excessive heating caused by an excess supply of current. It melts when heavy current flows through the circuit, thereby causing the circuit to become open
(b) Figure represents an MCB. An MCB is a device which functions as a fuse, but does not require replacement. MCB falls down to break the circuit when heavy amount of current flows through it. Once the fault is rectified, the MCB is reset.
(c) Figure (c) represents a DC generator. It is a device that generates electricity by rotating its rotor in a magnetic field. Thus, it converts mechanical energy into electrical energy.

Question 12:

Solve the following example.

a. Heat energy is being produced in a resistance in a circuit at the rate of 100 W. The current of 3 A is flowing in the circuit. What must be the value of the resistance?

b. Two tungsten bulbs of wattage 100 W and 60 W power work on 220 V potential difference. If they are connected in parallel, how much current will flow in the main conductor? 

CONTINUE

c. Who will spend more electrical energy? 500 W TV Set in 30 mins, or 600 W heater in 20 mins?

d. An electric iron of 1100 W is operated for 2 hrs daily. What will be the electrical consumption expenses for that in the month of April? (The electric company charges Rs 5 per unit of energy).

VISITORS COUNT

226649
Users Today : 772
Total Users : 226648
Views Today : 2182
Total views : 805766

Browse Categories

Archives