Friday, December 30, 2011

IX Atomic Structure (Discovery of a fundamental particle Electron,Proton and Neutron)

The first direct experimental evidence for the electrical nature of matter came from the experiments of Michale Faraday. He showed from his experiments that electricity is composed of particles called ‘atoms of electricity’.

It was George Johnstone Stoney, an Irish Physicist who first proposed the word ‘electron‘ for atom of electricity’ in 1891.His contribution to research in this area laid the foundations for the eventual discovery of particles by J.J. Thomson in 1897.

In 1878, Sir William Crooke, while conducting an experiment using a discharge tube, found certain visible rays travelling between two metal electrodes. These rays are known as Crooke’s Rays or cathode rays. The discharge tube used in the experiment is now referred to as Crookes tube or more popularly as
Cathode Ray Tube (CRT).

Cathode Ray Tube : It is a long glass tube filled with gas and sealed at both the ends. It consist of two metal plates (which act as electrodes) connected with high voltage. The electrode which is connected to the negative terminal of the battery is called the cathode (negative electrode). The electrode connected to the positive terminal is called the anode (positive electrode). There is a side tube which is connected to a pump. The pump is used to lower the pressure inside the discharge tube.

Discovery of electron 

Later, J.J. Thomson also found that when a high voltage of 10,000 V was applied between the electrodes present in a partially evacuated cathode ray tube at a pressure of 0.01mm of mercury, a bright spot of light was formed on the screen coated with a fluorescent material placed at the other end of the tube.

The Fluorescent material coated on the screen started to glow because it was struck by the ray which originated from the cathode. Since these rays were emitted by the cathode, he named these rays as cathode rays. Later, he named it as electrons.

Properties of cathode rays
1.The cathode rays travel in straight lines.
Cathode rays fall on a small object which is placed in between the cathode and anode.A shadow which is of the same shape as the object is observed on the wall opposite to the cathode.
2.Cathode rays are made up of small particles that have mass and kinetic energy.
Cathode rays fall on a light paddle wheel which is placed between cathode and anode. The wheel starts rotating.
3.The cathode rays are negatively charged particles

Cathode rays are passed through an electric field. The cathode rays are deflected towards the positive plate of electric field.

4. Cathode rays are passed through a magnetic field . The deflection of the rays is perpendicular to the applied magnetic field.
The direction of deflection indicates that the cathode rays constitute negatively charged particles. These negatively charged particles are called electrons

Characteristics of cathode rays : 
1) Cathode rays are not visible but their behavior can be observed with the help of a fluorescent or a phosphorescent. 
2) These rays travel from cathode to anode. 
3) These rays travel in straight lines in the absence of electric and magnetic fields. 
4) However these rays are deflected towards the positive end in electric field. Hence it was concluded that the rays constitute negatively charged particles and are known as electrons. 
These rays are also deflected in magnetic field.
5) The behavior and the properties of rays are independent of the nature of the cathode material and nature of the gas present in the cathode ray tube. 
These facts conclude that the electrons are the negatively charged fundamental particles present in all the substances.

Charge to mass ratio of Electron (e/me): 
The charge to mass ratio of electron was calculated by J. J. Thomson. Its value is equal to
Charge on the Electron (e) : The charge on the electron was calculated by Millikan in oil drop experiment as 1.60 x 10-19coulombs.  Now the mass of an electron can be derived as follows:

Related Post -Structure of Atom: IX

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Structure of Atom: IX NCERT Solution
Study material: Topic- Empirical formula and molecular formula
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Discovery of a fundamental particle protons
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How was the Discovery of Electron? (Structure of Atom)
Class IX Chemistry E-Notes Chapter Atomic Structure
IX Quick revision E Notes for chapter Structure of Atom
 Discovery of the Neutron - Ruther ford Model of Atom

CBSE VII SCIENCE Electric Current and its effects NCERTSolutions

Q1 What is meant by electric current?
Ans-Electric Current : Flow of electrons.
Q2 What is an electrc circuit?
Ans -Electric Circuit : The closed path in which electric current flows.
Q3 Under what conditions a circuit is said to be complete?
Ans-Current can flow through a circuit only if it is complete i.e. all its parts are made up of a conductor.
Q4 What is a switch?
Ans -Switch is used to close and open a circuit. When switch is ‘ON’ circuit is complete and current flows through it and when it is ‘OFF’ circuit breaks (air is an insulator) and flow of current stops.
Q5 Draw the symbols for various Components of an electric circuit ?
Cell : Source of electric current. 
 Battery : Combination of 2 or more cells 
Connecting Wires – generally insulated Copper wires. 
Electric Bulb – Key or switch-Open key-Closed key
Note : When cells are connected to form a battery positive terminal of one is always connected to negative terminal of the other.
Q6 What is a circuit diagram?
Ans—In an electrical Circuit when we replace electrical components with their symbols we call it Circuit diagram.

Q7 What do mean by heating effect of current?
Ans--When current flows through a metal wire it gets heated up, this is called heating effect of current. e.g. a glowing electric bulb becomes warm.
Q8 Name few appliances which use heating effect of current.
Ans--Appliances using heating effect of current Electric Iron, room heater, electric heater, geyser, hair dryers etc.
Q10 What are filaments of a bulb and a heater made up of?
Ans--In a bulb there is a thin wire called the filament made up of tungsten. When current passes through it, it glows and gets heated up. In a heater there is a coil of wire called element which is made up of nichrome. When current passes through element it becomes red hot and give out heat.
Q11 What are the factors on which amount of heat produced depends?
The amount of heat produced in a wire depends on
(A) Its material – better conductors produce less heat; e.g. Elements of electric appliances are made of nichrome whereas connecting wires are made up of copper which is a better conductor so they do not get heated up as the element.
(B) Its length – as length increases heat produced increases; e.g. elements are coiled in heaters to increase length.
(C) Thickness – as thickness increases heat produced decreases; e.g. lead wires of iron, heater etc. are thicker than normal connecting wire so that they don’t get heated up easily.
Q12 What is an electric fuse?
Ans---Electric Fuse - A Safety device in domestic circuit used to prevent electrical fire due to short circuit or overloading.
Q 13.Name any two effects of electric current.
Ans : Heating Effect : When an electric current flows through a wire, the wire gets heated. It is the heating effect of current due to resistance of wire that flow of current. This effect has many applications like Electric Heater, Light Bulb etc.
Magnetic effect : When an electric current flows through a wire, it produces magnetic effect around it that is detected by magnetic compass. Magnetic Effect of electric current use in Electric Bell, Motor, Fan etc.
Q 14.Fill in the blanks:
(a) Longer line in the symbol for a cell represents its ------- terminal.
(b) The combination of two or more cells is called a -------- .
(c) When current is switched ‘on’ in a room heater, it ----------.
(d) The safety device based on the heating effect of electric current is called a -------.
Ans: (a)negative (b) battery(c) gives out heat (d)fuse
Q 15. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell.
(b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks.
(c) An electromagnet does not attract a piece of iron.
(d) An electric bell has an electromagnet. 
(a)     (F)         (b) (T)              (c)(F)              (d)(T) 

CBSE 7th Waste Water Story management Solved Sample questions

Q1. State various uses of water.
Ans. Water is used for: • Drinking • Cooking • Washing clothes, utensils • Generating electricity • Bathing
• Habitat for various organisms etc.
Q2. What is waste water?
Ans. The dirty water which contains various impurities like dust, polythene bags, Vegetable peels, kitchen waste, oil & water that goes down the drains from sinks, showers, toilets, laundries etc is waste water. Waste water can not be used further.
Q3. What are the various causes of water pollution?
Ans. water is polluted by various factors like:
• Bathing of cattle in river bodies.
• Washing of clothes & utensils by people in rivers.
• Discharging wastes from factories, industries in nearby river bodies & ponds.
Q4. When is World Water Day celebrated?
Ans. World Water Day is celebrated on 22nd March.
Q5. What is sewage?
Ans. The waste water that is being generated at homes, industries, agricultural activities, human activities etc is called sewage.
Q6. What do you mean by “sewage treatment”?
Ans. Sewage treatment is a process of removing pollutants before it enters a water body or is refused.
Q7. Explain why is it harmful to discharge untreated sewage into Water bodies?
Ans. It is harmful to discharge the untreated sewage into the water bodies as it contains harmful substances. Most of it is water which has dissolved & suspended impurities which may pollute the water bodies & also harm the aquatic plants & animals.
Q8. What is sludge? How is it treated?

Thursday, December 29, 2011

Class VII Science Chapter Light Mirror and Lens Solved questions and Notes

Objective type Questions:
1. Out of convex mirror and concave mirror, whose focus is situated behind the mirror?
Ans: The focus of convex mirror is situated behind it.
2. For what position of an object, a concave mirror forms an enlarged virtual image?
Ans: Object between pole (P) and focus (F) of the concave mirror.
3. If the focal length of a concave mirror is 25cm. What is its radius of curvature?
Ans: Focal length = Radius of curvature / 2
25 = R / 2
R = 25 X 2 = 50cm.
4. A ray of light falls on a mirror normally. What are the values of angle of incidence and the angle of reflection?
Ans: Both angle of incidence and the angle of reflection are zero.
5. What is the focal length of a plane mirror?
Ans: Infinite.
6. Which spherical mirror is called a divergent mirror?
Ans: A convex mirror is called a divergent mirror.
7. What is the angle of incidence, when a ray of light falls on the spherical mirror from its centre of curvature?
Ans: The angle of incidence is zero, when a ray of light falls on the spherical mirror from its centre of curvature.
8. Name the type of mirror that always forms a virtual image for a real object?
Ans: Convex Mirror.
9. State the relation between radius of curvature and focal length of spherical mirrors.
Ans: Radius of curvature = 2 X focal length.
R = 2f.
10. Which of the two is a diverging lens? Convex lens (or) Concave lens.
Ans: Concave lens.
Short types Questions
Q1. What do you mean by reflection of light?
Ans. Bouncing back of light when it falls on a shiny surface is called reflection of light.
Q2. How does a path of light can be changed?
Ans. By reflecting it from a Polished Surface.
Q3. What are the laws of reflection?
Ans. Angle of incidence is equal to angle of reflection.Incedent, reflected ray & the normal lie on the same plane.
Q4. What is the nature of image formed in a plane mirror?
Ans. Virtual, erect, same image, laterally Inverted (left appears right & vice versa), at same distance from the mirror as the object.
Q5. Difference between real & virtual image? 
Ans Real Image
Image which can be obtained on a screen Image e.g.- Plane Mirror
Virtual Image
Image which cannot be obtained on a screen e.g. – Pinhole Camera, Photograph Camera.
Q6. What type of mirror – the inner surfact of the Spoon acts as and the outer surface of the spoon acts as ?
Ans. Inner surface of the spoon acts as Concave mirror and the outer surface of the spoon acts as concave mirror.
Q7. Which concave mirror called a converging mirror and a convex mirror called a diverging mirror?
Ans. Concave mirror is called a converging mirror because parallel rays of light fall on the mirror they Converge at a point called focus.
Convex mirror is called a diverging mirror because parallel rays of light fall on it they diverge after reflection.
Q8. What is the nature of image formed in a convex mirror?
Ans. It is always virtual, erect and diminished.
Q9. What is the nature of image formed in a concave mirror?
Ans. It depends on the portion of the object in front of the mirror. If the object is very close to the mirror the image is virtual, erect & magnified. As the distance increases image becomes real, inverted & its size keeps changing.
Q10. What are the uses of concave mirror?
Ans. 1) Used by the ENT Specialists, dentists. 
2.) Used as Shaving mirror. 
3) Used by makeup artists.
4) Used in torches & Car headlights to get a parallel beam of light.
Q11. What are the uses of Convex mirror?
Ans. 1) Used as a rear view mirror in vehicles because it has a wide field of view as images are smaller.
2) Used at metro Stations and big departmental stores to keep a check.
Q12. What are uses of Plane Mirror?
Ans. Plane Mirrors are used in optical testing, blind corners instrumental scales, Periscopes, telescope etc.
Q13. What is a lens?
Ans. A piece of transparent material bound by curved surfaces.
Q14. Difference between a convex lens & a Concave lens?
1. It is Thick at the Centre and thinner at edges
2. It is called converging lens
1. It is thin at the center and thicker at edges
2. It is called diverging lens.
Q15. Why a convex lens is called a converging lens and a concave lens a diverging lens?
Ans. If parallel rays of light fall on a convex lens they converge at a point.
If parallel rays of light fall on a concave lens they diverge as they pass through the lens.
Q16. What is the nature of image formed in a concave lens?
Ans. Virtual, erect & diminished.
Q17. What is the nature of image formed in a convex lens?
Ans. Same as in Concave mirror.
Q18. What are the uses of lenses?
Ans. 1.Magnifying glass – Convex lens.
2. To correct eye defects –people who can not see far off objects clearly wear Concave lens.
People who cant not see nearby object clearly wear Convex lens.
3. lenses are also used in Microscope, Telescope etc.
Q19. How is the rainbow formed?
Ans. Rainbow is formed after rainfall when Sun Shines. When sunlight passes through suspended raindrops it is split into seven colours “VIBGYOR’.
Q20. Where else you can see seven colours of sunlight?
Ans. You can see Seven colours of Sunlight when it falls over Soap bubbles, oil films, Shiny surfaces of CD etc.
Q 21. State the characteristics of the image formed by a plane mirror.
1. Image is Virtual
2. It is behind the mirror
3. Image is erect (means not inverted)
4. Image is of same size as the object
5. Image is at same distance from the mirror as the object is from the mirror.
Q22. Fill in the blanks
a. An image that cannot be obtained on a screen is called --------
b. Image formed by a convex ------------- is always virtual and smaller in size.
c. An image formed by a ------------- mirror is always of the same size as that of the object.
d. An image which can be obtained on a screen is called a ----------- image.
e. An image formed by a concave ------------ cannot be obtained on a screen.
Answers:  a) virtual image  b) convex mirror c) planed) real e) concave lens
For full chapter
CBSE Class 7 Science Chapters


Q1. Describe the different methods of asexual reproduction . Give examples.
A.There are different methods by which plants reproduce asexually. They are vegetative propagation, budding,fragmentation and spore formation. The vegetative parts of a plant are the roots, stems and leaves. When new plants are produced from these parts, the process is called vegetative propagation.
1. Budding- A bulb like projection grows on the parent organism. It grows and may eventually break away from the parent. E.g. yeast, hydra, corals, sponges.
2. Fragmentation- The organism breaks up into two or more fragments after maturation. These fragments grow into new individuals. E.g. spirogyra, hydra
3. Spore formation- A spore is a tiny, spherical and unicellular body protected by a thick wall. Under favourable conditions, a spore germinates and develops into a new individual. E.g. mosses, ferns, moulds
Q2. Describe the various ways by which seeds are dispersed.
A. Seeds and fruits are dispersed by agents like wind, water, animals and humans.
The pods present in these seeds dry up in the sun. This causes the pod to split with great force, thereby dispersing the seeds away from the parent plant.
Some seeds are dispersed by a special method called explosion. Examples are mustard, ladies finger, peas, bean, pod and castor.
Q3. How is fertilization brought about in a flower?
A. The zygote is formed by the fusion of the male and female gametes. This process is called fertilisation. After fertilisation, the ovary changes into a fruit. It may be either fleshy or dry.
Q4. Write 4 advantages of vegetative propagation.
A.The advantages are- 1. New plants can be produced quickly.
2. The plants so produced are exact copies of parent plants
3. Seedless plants can be easily propagated.
Q5. Differentiate between:-
1. unisexual flowers and bisexual flowers-
Bisexual flowers contain both – the stamens and the pistil. For example, mustard and rose.
Unisexual flowers have either the stamens or the pistil. For example, cucumber, maize and watermelon
2. sexual and asexual reproduction
In sexual reproduction, the male and the female gametes fuse to form seeds that eventually develop into new plants.
The seeds are formed inside the fruit. On the other hand, in asexual reproduction, a new plant is grown from any part of a plant other than the seeds.
3. cross pollination and self pollination
The transfer of pollen grains from the anther of one flower, to the stigma of another flower on another plant of  the same type, is known as cross-pollination.
The transfer of pollen grains from the anther to the stigma of the same flower or to the stigma of another flower on the same plant, it is termed self-pollination.
Q6. Why are flowers known as reproductive parts of a plant? are known as reproductive parts of a plant as flowers contain both male and female reproductive structures as  stamen and pistil respectively.
Q7. What is the significance of dispersal of seeds and fruits?
A. A plant produces a large number of seeds. They are required to be dispersed properly to get enough space, water and minerals and sunlight to grow healthy.
Q8. Why do spores can survive for a long time?
A. Spores are protected within a thick wall that makes it withstand unfavourable and extreme climate.
Q9. Which take less time to grow and bear flowers and fruits, plants produced by vegetative propagation or from seeds? Why?
Ans: A plant produced by vegetative propagation takes less time to develop and bear fruits and flowers. Plants grown from seeds require more attention and take good time to germinate and grow.
Q10. Write a short note on pollination.
A. It is the transfer of pollen grains from an anther to the stigma. Insects, birds and other animals help in cross pollination of flowers. Insects are attracted by the colour and scent of petals. Winds can also blow pollen grains. Such flowers such plants have flowers with small petals or with no petals at all.
Q11. Describe the process of seed formation.
A. After fertilization, petals, sepals and stamen wither away and fall off. Style and stigma also fall off. The ovule walls develop hard layers and seed develop. Each seed contains embryo enclosed in a protective seed coat.
Q12. Explain the process of fruit formation.
A. The ovary begins to swell. In time it becomes a fruit. So, a fruit is actually a developed ovary. Some fruits, like mangoes and apples are sweet and juicy. Sometimes, they become hard and woody forming the shells of nuts.
Q13. What are characteristics of seeds dispersed by water.
A. Seeds develop floating ability in the form of spongy or fibrous outer coat. E.g. coconut seeds have a thick coat of fiber that enables it to float in water. Lotus fruit has a spongy part that enables it to float.
Q 14.Define reproduction.
Ans:Reproduction is life process of producing new individuals from their parents of its own kinds. Q.15. What do you understand by the term 'leaf venetion'? What are the two types of leaf venetion?
Ans: The arrangement of veins in a leaf is called the leaf venation.
Reticulate Venation :In this the veins form a network like structure
Parallel venation : In this the veinsrun paralell to each other

Tuesday, December 27, 2011

X CBSE | NCERT Solutions Periodic Classification of Elements E- notes (Dobereiner Trieds)

OBJECTIVES OF THIS LESSON Periodic Classification of Elements
After completing this lesson, you will be able to:
! state different historical classifications of elements in brief;
! state main features of Mendeleev’s periodic table;
! explain the defects of Mendeleev’s periodic table;
! state modern periodic law;
! describe the features of the long form of periodic table;
! define various periodic properties;
! discuss the trends in various periodic properties in the periodic table.

The first classification of elements was as metals and non-metals. This served only limited purpose mainly because of two reasons:
1. All the elements were grouped in to these two classes only. The group containing metals
was very big.
2. Some elements showed properties of both-metals and non-metals and they could not be placed in any of the two classes.
Dobereiner’s triads
In 1829, Dobereiner, a German scientist made some groups of three elements each and called them triads.He observed that the
Atomic mass of the middle element of a triad was nearly equal to the arithmetic mean of atomic masses of other two elements.
Element symbol Atomic mass
Lithium, Li 7
Sodium, Na 23
Potassium, K 39
These elements are called Alkalies metal as they react with metal and form alkalies (Caustic solution)
Element symbol Atomic mass Element symbol Atomic mass
Calcium, Ca 40 Chlorine, Cl 35.5
Strontium, Sr 88 Bromine, Br 80
Barium, Ba 137 Iodine, I 127
These elements are called These elements are called Halogen
Alkalies Earth metal as they react with metal and form salt .
as their oxide are alkalies in nature
and exist in the Earth
Drawback: Dobereneir’s idea of classification of elements into triads did not receive wide acceptance as he could not arrange all elements in this manner.
Newland’s law of Octaves : In 1864 John Alexander Newland, an English chemist noticed that “when elements are arranged in the increasing order of their atomic masses. He found that
"every eighth element had properties similar to the first element.”
Newland called it the Law of Octaves. It was due to its similarity with musical notes .
Look carefully at the Newland’s arrangement of elements shown below:
Li Be B C N O F
(6.9) (9.0) (10.8) (12.0) (14.0) (16.0) (19.0)
Na Mg Al Si P S Cl
(23.0) (24.3) (27.0) (28.1) (31.0) (32.1) (35.5)
K Ca
(39.1) (40.1) Because his work The Royal Society , London awarded By Davy Medal in 1887
1.Newland could arrange elements in this manner only up to calcium (atomic mass 40 )out of a total of over sixty elements known at his time.
2. No Place given for forth coming elements.
3. He placed unlike elements in same slot like Co and Ni placed with F,Cland Iodine
4. When Nobel gas were discovered in 1900 law of octave fail and 9th element became similar to 1st.
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Sunday, December 25, 2011

CBSE MATH 9th 10th CBSE Sample paper for maths and science 2...

CBSE MATH STUDY: 9th 10th CBSE Sample paper for maths and science 2...

1. All questions are compulsory.
2. The question paper consists of 34 questions divided into four sections, namely
Section A : 10 questions (1 mark each)
Section B : 8 questions (2 marks each)
Section C : 10 questions (3 marks each)
Section D : 6 questions (4 marks each)
3. There is no overall choice. However, internal choice has been provided in 1 question of two marks, 3 questions of three marks and 2 questions of four marks each.
4. Use of calculators is not allowed.
10th_maths_sample_paper_2011-2012 - 1 Download File
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X phy Human Eye and Colourful World

CBSE PHYSICS: X phy Human Eye and Colourful World: X CBSE PHYSICS Questions for Practice 1. A person can see only objects beyond 1m. From his eyes. Name the defect of the eye. 2. Out of lig...

X Science Guess Paper – 2012 Carbon and its compou...

chemistry adda: X Science Guess Paper – 2012 Carbon and its compou...: Guess Paper – 2012 Class – X Subject - Science Carbon and its compounds Answer the following questions: Section A – one mark ea...

IX Science WORK, POWER AND ENERGY Guess Paper – 2...

CBSE PHYSICS: IX Science WORK, POWER AND ENERGY Guess Paper – 2...: 1. What is the work done by a force equal to? 2. Name two factors on which kinetic energy depends. 3. What is the commerc...

Saturday, December 24, 2011

CBSE Science 8th - Pollution Of Air And Water

Air pollution is described as any change in the composition of air either by physical or chemical methods so as to cause harmful effects on health.
The substances which contaminate the air are called air pollutants.
Sources of Air Pollution are :
1. Natural sources 2. Man-made (anthropogenic) sources.
Natural sources: Volcanic eruption, forest fire, sea salt sprays, biological decay, photochemical oxidation of terpenes oil , marshes, pollengrains, spores, etc.,
Man made sources : Industrial emissions, vehicles, aeroplanes, power stations and burning of fuels, etc.,
Mainly air pollution is caused due to burning of fuels to run vehicles, and from chimneys of factories and power stations.
The Green House Effect : Some of the infrared radiation from the earth passes through the atmosphere but most is absorbed and re-emitted in all directions by greenhouse gas molecules and clouds. This warms up the Earth’s surface and the lower atmosphere
Global Warming : CO2 is continuously being released because of human activities. On the other hand, area under forests is decreasing. Plants utilize CO2 from the atmosphere for photosynthesis, thereby decreasing the amount of CO2 in the air. Deforestation leads to an increase in the amount of CO2 in the air because the number of trees which consume CO2is reduced. Human activities, thus, contribute to the accumulation of CO2 in the atmosphere.
CO2 traps heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.
Ozone layer is thinning due to the emission of pollutant into the
atmosphere. Holes caused in the ozonelayer allow the harmful UV rays to reach the earth.
Radioactivity: Radio active minerals present in the earth’s crust are the sources of radioactivity in the atmosphere.
Acid Rain : Oxides of nitrogen, sulphur, carbon produced by combustion of coal, petroleum, etc,. dissolve in atmospheric water vapour. They form their corresponding acids like nitric acid, sulphuric acid, etc., and reach the earth’s surface as acid rain.
Effects of acid rain
● It irritates eyes and skin of human beings.
● It inhibits germination and growth of seedlings.
● It changes the fertility of the soil, destroys plants and aquatic life.
● It causes corrosion of many buildings, bridges, etc.,
Control of air pollution :Air pollution can be minimized by the following methods:
1. Use of crude oil should be avoided and use of high quality fuels, unleaded petrol, bio-diesel and compressed natural gas(CNG) should be recommended.
2. Use of automobiles should be minimized.
3. Industrial smokes must be filtered before releasing into the atmosphere.
4. By planting more trees to get pure air (O2) and reduce the CO2 content of the environment.
Water pollution: The contamination of water that changes in the physical, chemical and biological conditions of water is called water pollution. This makes water unfit for human consumption.
Whenever harmful substances such as sewage, toxic chemicals, silt, etc., get mixed with water, the water becomes polluted.
The substances that pollute water are called water pollutants.
1.Many industries discharge harmful chemicals into rivers and streams, causing the pollution of water.
2.Use of pesticides and weedicides . These chemicals dissolve in water and are washed into water bodies from the fields. They also seep into the ground to pollute ground water.
3. The bacteria present in the faeces of mammals.
4. Throwing untreated sewage directly into rivers.
Water which is suitable for drinking is called potable water.
Water can be made safe for drinking:
1. By filtering water. A popular household filter is a candle type filter.
2. By boiling Water.Boiling kills the germs present in the water
3. Chlorination is a commonly used chemical method for purifying water.It is done by adding chlorine tablets or bleaching powder to the water
  1. Water pollution is the contamination of water by substances harmful to life.
  2. Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water.
  3. Water which is purified and fit for drinking is known as potable water.
  4. Water is a precious natural resource. We must learn to conserve it.

Friday, December 23, 2011

CTET/TET Sample Model Question Paper 2012

CTET/TET Sample Model Question Paper 2012 Child development and Pedagogy
CTET examination papers can be downloaded from given link
English Language
CTET or Other state Tet model paper

Sunday, December 4, 2011

CBSE PHYSICS IX Physics Sound NCERT Solutions

Explain how sound is produced by your school bell.
When the bell continues to move forward and backward, it creates a series of compressions and rarefactions. In this  way a bell produce the sound .
Why sound waves are called mechanical waves?
Sound waves need the material medium to vibrate and propagate. Hence, these waves are known as mechanical waves. Sound waves propagate through a medium because of the interaction of the particles present in that medium.
Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Sound needs a medium to propagate. Since there is no material medium on the moon due to absence of atmosphere, you cannot hear any sound on the moon.
Page 166 : Which wave property determines (a) loudness, (b) pitch?
(a) Amplitude of sound wave determines the loudness of a sound. The amplitude of a sound directly proportional to amplitude of wave. If the amplitude of a sound is large, then the sound produced will also be loud.
(b) Frequency of sound wave determines the pitch of a sound . The pitch of a sound is proportional to its frequency. High pitched sounds have high frequency
Guess which sound has a higher pitch: guitar or car horn?
The frequency of the vibration of a sound produced by a guitar is greater than that produced by a car horn. As we know that the pitch of a sound is directly proportional to its frequency, the guitar has a higher pitch than a car horn.
Page 166 : What are wavelength, frequency, time period and amplitude of a sound wave?
Wavelength: The distance between two consecutive compressions or two consecutive rarefactions  is known as the wavelength. Its SI unit is metre (m).
Frequency: The number of oscillations produced by vibrating body in one second is known as the frequency of a sound wave. It is measured in hertz (Hz).
Amplitude: The maximum height reached by the crest or trough of a sound wave is called its amplitude.
How are the wavelength and frequency of a sound wave related to its speed?
Speed of sound wave is product of wavelength and frequency of a sound wave
Speed ( v) = Wavelength × Frequency = ν λ
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Frequency of the sound wave, v = 220 Hz Speed of the sound wave, v = 440 m/ s
Speed = Wavelength × Frequency
Wavelength of a sound wave = Speed of the sound wave/ Frequency of the sound wave
= 440 m/s ÷ 220 Hz = 2m
Hence, the wavelength of the sound wave is 2 m.

A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?
You know that the time taken to complete two successive compressions or two consecutive rarefactions is called the time period of the wave.
Time period of the wave = 1/Frequency Hence, time period is reciprocal of the frequency of the wave
Now, Time period of the wave=1/500=0.002 second
Page 166 : Distinguish between loudness and intensity of sound.
a) Intensity of sound waves is defined as the average energy transported per second per unit area perpendicular to the direction of propagation.
b) It is measured in Js-1m-2 or Wm-2.
c) The intensity of sound in air depends on the square of the frequency and the square of the amplitude.
a) The loudness of sound is defined as the degree of sensation of sound produced in the ear
b) The loudness of a sound depends on its amplitude.
c) The amplitude of a sound decides its intensity, which in turn is perceived by the ear as loudness.
Page 167 : In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?
The speed of sound depends on the nature of the medium. Sound travels the fastest in solids. Its speed decreases in liquids and it is the slowest in gases. Therefore, for a given temperature, sound travels fastest in iron.
Page 168 : An echo returned in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m/s ?
Speed of sound, v = 342 m/ s Echo returns in time, t = 3 s
Distance travelled by sound = v × t = 342 × 3 = 1026 m
In the given time interval, sound has to travel a distance that is twice the distance of the reflecting surface and the source.
Hence, The actual distance of the reflecting surface from the source =1026/2=513m
Page 169 : Why are the ceilings of concert halls curved?
Ceilings of concert halls are curved so that sound after reflection (from the walls) spreads uniformly in all directions due to irregular reflection.
Guess Paper for Class - IX-Physics Chapter : Sound
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IX-Physics for term-II Sound CBSE Test paper      Download File