Class 11 English The Voice of Rain summary

“The Voice of the Rain“

by Walt Whitman

 

1. Poem : “The Voice of the Rain”

   Poet   :   Walt Whitman

 

2. Summary of the Poem

• The poet asks the rain, “And who art thou?” and strangely, the rain replies, calling itself the “poem of earth.”
• The rain says that it is born from the earth but cannot be seen since it is in the form of vapors.
• It rises into the sky to form clouds and then falls back to the earth in the form of drops.
• It removes droughts and washes away even the tiniest particles.
• It falls on dry seeds, which appear lifeless, and helps them sprout into saplings.
• It gives life to its own origin, i.e., earth; it purifies and beautifies the earth.
• Like a song coming out from the heart, it spreads joy all around and seeps back into the earth.

 

3. Poetic Devices Used in the Poem
4. Personification:

“Said the voice of the rain” – Rain speaks throughout the poem.

 

2. Antithesis:

“All together changed, and yet the same” – Two opposite ideas have been pulled

together to describe the continuous cycle of rain.

 

3. Metaphor:

“I am the poem of the earth.”

 

4. Theme of the Poem
5. The poet portrays the life cycle of rain and compares it to a song.
6. The poem discusses a conversation between the poet and the rain, where the rain calls itself the “poem of the earth.”
7. The rain describes its journey:

• It rises as vapors from the land and sea.
• It forms clouds and falls back to the earth to refresh drought-filled lands.
• This helps seeds grow into beautiful greenery.

4. The poet compares his role in creating poems to the role of rain, as both bring life and beauty.
5. The rain symbolizes the cycle of life in all living things.
6. The rain completes the cycle of life, much like the life of all human beings.

 

 

Class – 8^th

Crop Production and Management

 

• All living organisms require food.

• The energy from food is utilised by an organism for carrying out its various life processes such as digestion, respiration, and excretion.

• Plants can make their food themselves but animals including humans cannot.

• We get our food from plants or animals, or both.

Plants of the same kind that are grown and cultivated as a source of food in a large cultivable land is called a crop.

Kya hum koi bhi crop kabhi bhi uga sakte hai? Nahi, har crop different hai jisko different weather conditions different soil and nutrients required hai.

Types of Crops

Rabi Crop

Crops which are grown in the winter season (from October to March) are called Rabi crops.

For Example: Wheat, Gram, Pea, Mustard, and Linseed.

Kharif Crop

Crops which are sown in the rainy season (from July to October) are called Kharif crops.

For Example: Paddy, maize, soyabean, groundnut, and cotton.

Zaid Crops (or Summer Crops)

The crops which are grown in the summer season are called zaid crops.

For Example : Moong, muskmelon, watermelon, cucumber, gourd and bitter gourd.

Cultivation of crops

• Soil Preparation:It involves loosening and tilling of the soil (i.e., ploughing and watering).

Selection of Seed – Quality of the Seeds

• The quality of the seed is an important factor that determines the crop yield.

• The selection of good seeds is done by putting the seeds in water.

• The dead and damaged seeds become hollow and float on water, whereas the good seeds sink.

• Sowing:Sowing is the process of putting seeds in the soil.

• Adding Manure and Fertilisers:The substances, which are added to the soil in the form of nutrients to improve the production of the crops and fertility of the soil are called manure and fertilisers.

• Irrigation:Supply of water to crops at appropriate intervals is called irrigation.

• Protection from Weeds:Weeds are the unwanted plants that grow along with the crops. Its removal is a must for the better growth of the crops. These can be controlled by spraying certain chemicals, called weedicides, like 2, 4-D.

• Harvesting:The cutting of the crop after it is mature is called harvesting.

• Storage: If the crop grains are to be kept for a longer time, they should be safe from moisture, insects, and rats.

 

Class – IX                                CSCE TUTORIAL                                       Biology

Tissues

 

Tissues

Tissues are the cluster of structurally and functionally similar cells arranged to give the highest possible efficiency of the function they perform. All cells of a tissue have a common origin.

Characteristics of Tissues

1. There is division of labour in multicellular organisms, as different group of cells perform different functions.
2. Tissues become organized to form organs and organs thereby develop into systems.
3. Due to improved organisation and higher efficiency, multicellular organisms have higher rate of survival than unicellular organisms.

 

Plant Tissue

On the basis of dividing capacity, plant tissues can be classified into two fundamental types as:-

1). Meristematic Tissue

The tissue whose called divide actively throughout life is known as meristematic tissue. It is also called as growth tissue and is found in the growing regions of plant like root and shoot tip. The process of cell division in meristematic tissue is prominent to get new cells. Cell forming in this tissue are active and have dense cytoplasm, thin cellulose walls and prominent nuclei. These are classified on the basis of  the regions where they are present as growth of plants occurs only in certain specific regions.

1. Apical Meristem – These are present at growing tips of stems and roots. Thus, are helpful in increasing the length of the stems and the roots. It acts as pro-meristem having actively dividing cells, giving rise to other meristems.
2. Intercalary Meristem – These are present at the base of the leaves or internodes on twigs. It helps in longitudinal growth of plants by adding primary tissues.
3. Lateral Meristem – These are present on the lateral sides of stem and roots. It helps in increasing the girth of the stem or root.

 

2). Permanent Tissue

This tissue is formed from the cells of meristematic tissue when they loose their ability to divide and have attained a permanent shape, size and function by the process called differentiation.

1. Simple permanent tissue
   It is made up of only one type of cells, the cell forming these tissues are similar in structure and function.
2. Parenchyma
   They are present in cortex and pith of stem and roots and also in mesophyll of leaves.

Characteristics of Parenchyma are:-

1. The cells are isodiametric, i.e. all sides equal with thin cell walls made up of cellulose.
2. Cells are loosely packed with large spaces between cells (i.e. intercellular spaces).
3. Each cell encloses a large vacuole and a peripheral cytoplasm containing nucleus.

Functions of Parenchyma are :-

1. It stores and assimilates food and serves as food storage tissue.
2. It provides support to plant due to its turgidity property.
3. When the parenchyma cell contains chlorophyll in some situations, it performs photosynthesis. Such Parenchyma tissues are called Chlorenchyma.
4. In aquatic plants, large air cavities are present in parenchyma cells in order to give buoyancy to plants which help them to float. Such type of parenchyma tissue is called Aerenchyma. 

   Aerenchyma

1. The presence of intracellular spaces between the cells allows the exchange of gases.
2. It serves as a packing tissue to fill the spaces between other tissues and maintains the shape and firmness of the plants.
3. Collenchyma

These are the tissues which are found in leaf stalks below the epidermis, leaf mid-ribs and herbaceous dicot stems.

Characteristics of Collenchyma are:-

1. Cells are living, elongated and irregularly thickened at the corners.
2. Cell wall has extra deposition of cellulose and pectin and possesses simple pits.
3. They have very little intercellular spaces.
4. They contain chloroplast.

Functions of Collenchyma are:-

1. It provides mechanical support and elasticity or flexibility to plants.
2. It allows easy bending in various parts of a plant without breaking.
3. They manufacture sugar and starch when possess chloroplasts.
4. Sclerenchyma
   It is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts.

Characteristics of Sclerenchyma are:-

1. The cells of sclerenchyma tissue are dead and do not contain protoplasm.
2. The cells are long and narrow in appearance.
3. Cells are of two types : fibres and sclereids (grit cells or stone cells).
4. Cell wall are thickened due to lignin deposition which acts as cement and hardens them.
5. A prominent middle lamella exists between two cells.
6. Due to the presence of thick walls, there is no internal space inside the cell.

Functions of Sclerenchyma are:-

1. It is known to be chief mechanical tissue which makes plant hard and stiff.
2. It provides strength and enables the plant to bear various stresses.
3. It forms protective covering around seeds and nuts.
4. It gives rigidity, flexibility and elasticity to the plant body.

 

Protective Tissue

The protective tissue is meant to provide protection to the plants from undue loss of water and retain adequate water in them. The two types of protective tissues present in plants are:-

(i) Epidermis                                                         (ii) Cork (or Phellum)

• Epidermis

Epidermis is the outer covering of the plant. It is meant to provide protection to all the parts of the plant. On the aerial parts of the plant, Epidermal cells often secrete a waxy, water-resistant layer on their outer surface which provides protection against loss of water, mechanical injury and invasion of parasitic fungi. Cells of epidermis tissue form a continuous layer and no intercellular spaces due to protective role.

Epidermal cells of leaf bear small pores known as stomata. These are enclosed by two kidney shaped cells called guard cells. Stomata are responsible for the exchange of gases with the atmosphere and for the process of transpiration. The epidermal cells of roots whose main function is water absorption bear long hair like outgrowths called root hair that greatly increase the total absorptive surface area and helps the roots to absorb water and nutrients from the soil. In desert plants, epidermis has a thick waxy coating of cutin on its surface to prevent water loss. Cutin is a chemical substance with waterproof quality.

 

• Cork

It is the strip of secondary meristem which replaces the epidermis of older stems. Cells of cork are dead, compactly arranged and have no intercellular spaces. It forms bark of the tree. A chemical called suberin is present in their walls which make them impervious to gases and water. It prevents desiccation, infection and mechanical injury.

 

Complex Permanent Tissue

It is made of more than one type of cells having a common origin. The cells look different from each other. Regardless of different appearances, all the cells co-ordinate to perform a common function.

Types of Complex Permanent Tissue are:-

• Xylem

It is a vascular and mechanical conducting tissue, also known as wood. The cells of xylem have thick walls and many of them are dead. It transport water and minerals from roots to other parts of the plant. It provides mechanical strength to the plant. Xylem consist of various types of elements which are :-

1. Tracheids
   These are long, tubular, elongated, dead cells with lignified walls and tapering ends. They transport water and minerals vertically. They possess pits for transport of water from cell to cell.
2. Vessels
   These are long, tube like structures, formed by a row of cells, placed end to end. These  are dead cells with lignified walls. These are shorter and wider than tracheids due to their thick walls and broad lumen.
3. Xylem Parenchyma
   These are the only living cells of xylem with thin cell walls. It stores food and help in the sideways conduction of water.
4. Xylem Fibres
   They have elongated dead cells with tapering ends and thick cell walls. They are sclerenchyma fibres associated with Xylem.

• Phloem

It is another kind of living conducting tissue, also known as bast. It transport food from leaves to other parts of the plant. Materials can move in both direction in it. All phloem cells are living except phloem fibres.

1. Sieve tubes
   These are tubular cells with walls perforated by numerous pores and are called sieve plates. Nucleus is absent, but present in young cells. They have thin layer of cytoplasm.
2. Companion cells
   These are small elongated cells having thin walls. They have dense cytoplasm and prominent nucleus. They are connected to sieve tubes with numerous plasmodesmata. They help in maintain pressure gradient in sieve tube.
3. Phloem parenchyma
   These are thin-walled living parenchymatous cells. They help in storage and slow lateral conduction of food by plasmodesmatal connections.
4. Phloem fibre
   These are thick-walled, elongated, dead sclerenchymatous cells having narrow lumen. They provide mechanical strength to the tissue. Bast fibers obtained from plants like jute, hemp, flex etc. have commercial value.

 

Animal Tissue

1. Epithelial Tissue
   It is the simplest protective tissue of the animal body, which covers most organs and cavities of the body. Cells of epithelial tissues are tightly packed and form a continuous sheet. They have a very small amount of cementing material between them. It forms a barrier to keep different body systems separated from each other. It is separated from underlying tissue by an extracellular fibrous basement membrane containing collagen.

On the basis of shape and arrangement, epithelial tissues further classified as:-

1. Squamous Epithelium

   ‘Squama’ means scales. It has scale like appearance, it is also known as tessellated or pavement epithelium.
   It is further categorized as :-
   1. Simple Squamous Epithelium
   The cells are very thin and flat and appear as tiles over a floor. It is single layered and closely fitted. It forms a delicate lining of blood vessels and lung alveoli, where substance transport occurs through a selectively permeable membrane.
   2. Stratified Squamous Epithelium

    

2. Cuboidal Epithelium
3. Column Epithelium
4. Ciliated Columnar Epithelium

 

 

CSCE TUTORIAL

CHAPTER 15

IMPROVEMENT IN FOOD RESOURCES

 

1. What is the most important source of irrigation in India?

Ans:  Rain water i.e., Monsoons.

 

2. What are the traditional ways of irrigation used in India?

Ans:  There are many traditional ways of irrigation used in our country:

1. Wells – There are two types of wells, dug wells and tube wells. In a dug well water is collected from the water bearing strata whereas in a tube well water is pumped out from the deeper strata through pumps.
2. Canals – In this system water from one or more reservoirs or from rivers. The main canal is then branched into distributaries to irrgate fields.
3. River lift system – In areas where the canal flow is irregular/ insufficient due to inadequate reservoir release, the lift system is used. Water is directly drawn from the rivers for supplementing irrigation in areas that are closed to the rivers.
4. Tanks – These are small storage reservoirs which receive and store run-off of smaller catchment areas.

 

3. What are the two fresh initiatives for increasing the availability of water for agriculture? What is the advantage of building check dams?

Ans.  Rain water harvesting and water shed management are the two fresh initiatives to supply water for irrigation. This involves building                  small check dams which  lead to an increase in ground water levels. Stop the rain water from flowing away thus reduces soil erosion.

 

4. What do you mean by:
   1. Mixed cropping – Mixed cropping is growing two or more crops simultaneously on the same piece of land. For example, wheat + gram or wheat + mustard. This reduces the risk and gives some insurance against failure of one of the crops.
   2. Inter-cropping – It is growing of two or more crops simultaneously on the same field in a definite pattern. A few rows of one of alternate with a few rows of another crop for example soya bean + maize or finger millets + cow pea. The crops are selected in such a way that their nutrient requirements are different. This ensures maximum utilization of nutrients supplied and also prevents pests and diseases from spreading in a field.
   3. Crop rotation – The growing of different crops in a pre-planned succession is called crop rotation. Depending on the duration different combination of crops can be used. The availability of moisture and irrigation facilities decides the choice of crops. It can help the farmer to get two or three crops in a year with good harvests.

 

5. What are weeds? Give examples. How are they harmful to the crops?

Ans:  Weeds are unwanted plants growing in the field along with the main crops.
For example, Xanthium and Parthenium, Cyperinus rotundus.
They compete with the main crop for nutrients, water, space etc. Therefore, they need to be removed from the field in the early stages            of crop growth for a good harvest.

 

6. What are the various ways in which insect pests attack the plants?

Ans:  Three ways in which insect pests attack the plants are-

1. They cut the root, stem and leaf.
2. They suck the cell sap from the various parts of the plants.
3. They bore into the stem or fruits. In these ways the plant health is harmed by the insect pests.

 

7. How weeds, insects and diseases can be controlled in plants?

Ans:  Diseases in plants are caused by pathogens such as bacteria, fungi, virus etc. Weeds, insects and diseases can be controlled by various methods.

1. By using pesticides which include herbicides, insecticides, fungicides etc. These chemicals are sprayed on crop plants or used for treating the seeds and soil. However, excessive use of these chemicals creates problems as they are poisonous substances harming the environment and plants and animals.
2. Weeds control methods also include mechanical removal.
3. Growth of weeds can also be prevented by proper seedbed preparation, inter or mixed cropping pattern etc.
4. To avoid pests, pest resistant varieties can be used. Summer ploughing is also helpful in removing weeds. In this method fields are ploughed deep in the summer to destroy weeds and pests.

 

9. What factors may be responsible for losses of grains during storage?
   Ans:  Storage losses in agriculture can be very high. factors responsible for such losses are:Biotic – insects, rodents, fungi, mites, bacteria etc.

   Abiotic – inappropriate moisture and temperature of the storage area.

10. How does storage losses cause harm to agricultural produce?

Ans:  Storage losses cause degradation in quality, loss in weight, poor germinability and discoloration of produce resulting in poor marketability.

 

10. What are the various methods to avoid loss of grains during storage?

Ans:  Storage losses of the grains can be reduced by strict cleaning of the produce before storage, proper drying of the produce first in sunlight and then in shade and fumigation using chemicals which can kill the pests.

 

11. What do you mean by animal husbandry?

Ans:  The scientific management of animal livestock is called animal husbandry. It includes feeding, breeding and disease control.

 

12. Give two reasons for which cattle farming is done.

Ans:  Cattle husbandry is done for two purposes – milk and draught labour for agricultural work such as tiling, ploughing etc.

 

13. What is the lactation period?

Ans: The period of milk production after the birth of calf is called the lactation period.
Milk production can be increased by increasing the lactation period. For this reason exotic breeds  like Jersey and Brown Swiss (for long lactation period) are crossbred with Indian breeds like Red Sindhi and Sahiwal (excellent resistance to diseases) to get animals with both the desired qualities.

 

14. Name two milk producing cattle in India.

Ans: Bos indicus (Cow) and Bos bubalis (buffalo)

 

15. What are the food requirements of dairy animals?

Ans:  The food requirements of the dairy animals are of two types –

1. maintenance requirements – the food required by the animal to live a healthy life.
2. milk producing requirements – the food required by the animal during lactation period.

 

16. What are the two major components of animal feed?

Ans:  Animal feed includes

1. roughage – largely fibre
2. concentrates – low in fibre and contains relatively high levels of proteins and other nutrients.

 

17. How does one get to know if a cattle is sick?

Ans:  A healthy animal feeds regularly and has a normal posture.

 

18. What are the different types of parasites affecting the health of animals?

Ans:  The animal may get affected by both external and internal parasites. The external parasites live on the skin and mainly cause skin  diseases.   The internal parasites like worms affect the stomach and intestine while flukes damage the liver.

 

19. What do you mean by poultry farming?

Ans:  Poultry farming is undertaken to raise domestic fowl for egg production and chicken meat.

 

20. Name Indian and exotic breeds of poultry birds.

Ans:  The cross breeding programmes between Indian ( Aseel) and exotic ( Leghorn) breeds for variety improvement are focused on to develop new varieties of poultry birds.

 

21. What are the various traits for which cross breeding programmes are carried out for poultry birds?

Ans:  i)       Number and quality of chicks.

1. ii) Dwarf broilers for commercial chick production.

iii)     Summer adaptation capacity.

1. iv) Low maintenance requirements.
2. v) Reduction in the size of the egg-laying birds

 

22. Explain the dietary requirements of the poultry birds.

Ans: The dietary requirements for broilers are different from the layers. Broiler

chickens are fed with vitamin rich supplementary feed for good growth rate and better feeding efficiency. The daily ration for the broilers is protein rich with adequate fats. The level of vitamin A and K is kept high in poultry feeds.

 

23. What management practices are used for good production of poultry birds?

Ans.  For good production of the poultry birds temperature management and hygienic conditions are required for housing. Good poultry feed and prevention from diseases and pests are also needed to have a good yield of poultry birds.

 

24. What are the two ways in which fish production is carried out?

Ans: There are two ways of fish production. One is from natural sources which is

called capture fishery. The other is fish farming, also called culture fishery.

 

25. What are the various products of fish farming?

Ans:  Fish farming is done for producing finned true fish as well as shellfish such as prawns and molluscs.

 

26. Name important varieties of fish obtained in India.

Ans:  Popular marine fish varieties in India include pomphret, mackerel, tuna, sardines and Bombay duck. Some marine fish are also farmed in sea water. This includes finned fishes like mullet, bhetki and pearl spots. shellfish like prawns, mussels and oysters. Oysters are cultivated for the pearls they make.

 

27. What do you mean by mariculture?

Ans:  Fish farming done in ocean water is called mariculture.

 

28. How is fish farming done in combination with rice farming?

Ans:  Sometimes fish are also grown in paddy fields. This helps the farmer to increase his income.

 

29. What are brackish waters?

Ans:  Brackish water resources are the one where the sea water and fresh water mix together e.g. lagoons and estuaries. These places are important fish reservoirs.

 

30. How are the schools of fish located?

Ans:  Large schools of fish are located by using satellites and echo-sounders. Then these fish can be easily captured by using large fishing nets.

 

31. What is composite fish culture? What are the advantages of this system? State its one limitation and also the solution to this limitation.

Ans:  Composite fish farming is a method of intensive fish farming. In such a system a combination of five or six fish species is used in a single fish pond.

These species are selected in such a way that they do not compete with each other for food as they have different food habits.

Some of these species are surface feeders (Catlas), Rohus feed in the middle zone, while Mrigals and Common carps are the bottom feeders. Green carps feed on the weeds. Together these species can use all food in the pond without competing with each other. This increases the fish yield from the pond.

 

Limitation – Many of these fish breed only in monsoon season, even if fish seeds are collected from the wild, it can be mixed with that of other species as well. So a major problem is to obtain good quality seeds.

This problem can be overcome by hormonal stimulation of fish in the ponds to ensure supply of pure fish seeds in desirable quantities.

 

32. Why is bee keeping done? How does it help the farmer?

Ans:  Beekeeping is done to obtain honey which  is widely used and also to obtain bee wax which is used for various medicinal purposes.

 

33. List various varieties of honey bee reared in India.

Ans:  The local varieties of honey bees used for commercial honey production are Apis cerana indica (Indian bee), Apis dorsata (The rock bee) and Apis florae (The little bee). An Italian bee variety, Apis mellifera, has also been used to increase the production of honey. This variety has high honey collection capacity and they sting less. Also, they stay in a given bee hive for a longer period of time.

 

34. What is an apiary?

Ans:  Large bee farms for commercial honey production are called apiaries. Rearing

and breeding of honey bees for honey production is called apiculture.

 

35. What are the factors on which the quality of honey depends?

Ans:  The value or the quality of honey produced depends on the pasturage or the

flowers available to the bees for collection of nectar and pollen. Besides this the kind of flowers available also determine the taste of the honey.

CSCE TUTORIAL

SOUND

 

1. Sound is a form of energy which produces a sensation of hearing in our ear.

2. Production of sound – Sound is produced by vibration of an object.

3. Vibration means to and fro motion of an object.

4. The sound of the human voice is produced by the vibrations of the vocal cords.

5. Sound produced by a bee is due to flapping of its wings. When a bird flaps its wings, sound is produced.

6. Propagation of sound – Sound is produced by a vibrating object. The matter or substance through which sound is transmitted is called a medium. When an object vibrates, it sets the particles of the medium around it vibrating. The particles do not travel all the way from the source of sound to the listener. A particle of the medium in contact with the vibrating object first displaces from its equilibrium position which then exerts force on the next adjacent particle. After displacing the second particle the first particle comes to rest. This disturbance thus passes to through the medium until it reaches our ear. Thus, only energy gets transferred in the form of sound waves and not the particles as the sound propagates.

7. A sound wave is a disturbance that moves through a medium when the particles of the medium set the neighbouring particles into motion. Since sound waves are characterized by the motion of particles in a medium, they are called the mechanical waves.

8. Sound as a series of compressions and rarefaction – Air is the most common medium through which sound travels. When a vibrating body moves forward, it pushes and compresses the air in front of it creating a region of high pressure called compression (C). This compression starts to move away from the vibrating body. When the vibrating body moves backwards, it creates a region of low pressure called rarefaction (R). As the object moves to and fro rapidly, this sets a series of compressions and rarefactions in the air. This makes the sound to propagate in the air.  ( Pressure is related to the number of particles of the medium in the given volume) More density of air means more pressure while less density of air means less pressure. Thus, propagation of sound can be visualized as propagation of density variations or pressure variations in the medium.

9. Sound needs a medium to travel – Sound waves are called longitudinal waves as they travel in the form of a series of compressions and rarefactions. In these waves the individual particles of the medium move in the direction parallel to the direction of motion of the wave. The particles of the medium are not actually moving, they only vibrating back and forth about their position of rest.

   Since the sound moves through the medium by to and fro motion of the particles, thus sound requires the presence of the material medium for its propagation.

10. Transverse wave – In a transverse wave particles do not oscillate along the direction of propagation but oscillate up and down about their mean position as the wave travels. Thus, in case of transverse wave, the particles move up and down perpendicular to the direction of motion of the wave. For example, if we drop a pebble in a pond of water, the ripples formed on the surface of water is an example of the transverse wave.

    Another example of the transverse waves is light wave. In light wave, however, no material medium is required for the propagation of wave, so they are not mechanical waves.

11. Characteristics of a Sound wave – There are three characteristics of sound.
12. Frequency – The number of oscillations per second is called the frequency of a wave. The SI unit of frequency is Hertz (Hz). It is usually represented by ‘𝛎)’ (Greek letter ‘nu’)
13. Wave length – Sound waves are a series of compressions and rarefactions. Compressions are a region of high pressure represented by the upper portion of the curve shown below:
    Rarefactions on the other hand are the regions of low pressure where particles are far apart and are shown by lower portions of the wave.
    A peak is called a crest and a valley is called a trough of the wave.
    Wavelength is the distance between two consecutive crests or two consecutive troughs and is represented by the (Greek letter ‘Lambda’) and its SI unit is m.  – Greek letter ‘Lambda’.
    Time period – The time taken by two consecutive compressions or rarefactions to cross a fixed point. The time taken to complete one oscillation is called the time period of the sound wave. It is represented by the letter ‘T’. The SI unit of time period is second (s).
    Relation between frequency and time period – Time period and frequency are reciprocal of each other.

14. Pitch – The shrillness of sound is called pitch. It is how our brain interprets the frequency of a sound. It depends on the frequency of sound. The faster is the vibrations of a source, the higher is its frequency and thus higher is its pitch. Thus, a high pitch sound corresponds to more compressions and rarefactions passing through a fixed point per unit time.
15. Loudness – The magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of the wave. It is usually represented as ‘A’. For sound its SI unit is the SI unit for density or pressure.
    The loudness of sound is determined by its amplitude which further depends on the force with which an object is made to vibrate. Larger is the amplitude louder is the sound produced. A sound wave spreads out from its source in all directions. As it moves away from the source its amplitude as well as the loudness decreases because the particles lose the energy associated with them.
16. Quality or timbre of sound – The quality or timbre of sound is that characteristic which enables us to distinguish one sound from the other even if they have same pitch and loudness. A sound that is more pleasant is said to be of rich quality.
17. Tone – Sound of a single frequency is called a tone. The sound which is produced due a mixture of several frequencies are called a note. And is pleasant to our ear. Unpleasant sound is called noise.
18. Speed of sound – The distance which a point on a wave such as compression or rarefaction, travels per unit time.
    Speed, v = distance / time
    Speed = wavelength x frequency
    Speed of sound remains almost same for all frequencies in a given medium under the same physical conditions.

Ex 12.1) A sound wave has a frequency of 2 kHz and wave length 35 cm.

How long will it take to travel 1.5 km?

Ans: Frequency = 2 kHz = 2000 Hz

Wavelength = 35 cm = 35/100 m = 0.35 m

Speed  = Frequency x Wavelength
= 2000 x 0.35
= 700 m/s

Distance = 1.5 km = 1.5×1000 m = 1500 m

V = d/t

t = d/v = 1500/700 = 2.1 s

 

In text questions (page number 166)

3. wavelength = ?

Frequency = 220 HZ

Speed = 440 m/s

Speed = frequency x wavelength

Wavelength = speed / frequency

= 440 / 220 = 2 m

 

4. 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?

Ans:  Frequency = 500 Hz

Time period = 1 / frequency

= 1/500 s = 0.002 s

17. Intensity of sound – The amount of sound energy passing each second through a unit area is called the intensity of sound. Loudness and intensity are not same but related. Loudness refers to the measure of the response of our ear to the sound. Even though two sounds are of equal intensity but one may appear louder than the other because our ear detect it better.
18. Speed of sound in different media – Speed of sound varies in different media and also depends on the temperature of the media. Speed of sound decreases as we go from solid to liquid to gaseous state. It increases with increase in temperature. For example, the speed of sound in air is 331 m s^–1 at 0 ^°C and 344 m s^–1 at 22 ^°C .

19. Reflection of Sound – Sound bounces off after striking a surface (hard). Like light sound also follow the same laws of reflection.
20. The angle of incidence of sound wave is same as the angle of reflection.
21. The incident wave, the reflected wave and the normal to the point of incidence all lie in the same plane.

20. Echo – Reflection of sound after striking a hard surface which can be heard is called echo. The sensation of sound persists in our brain for about 0.1 s. to hear a distinct echo the time interval between the original sound and its reflection must be at least 0.1 second. If the speed of sound is taken to be 344 m/s at any given temperature e.g., 22^o C in air, the sound must go and reach back after reflection after 0.1 s
    Speed    = distance / time
    Distance = speed × time

=    344 × 0.1 = 34.4 m
So, for hearing an echo. The surface should be at least 17.2 m away from the source of sound.

Echoes may be heard more than once. This happens due to multiple reflections.  

21. Reverberation – A sound created in a big hall will persist by repeated reflection from the walls until it is reduced to a value where it is no more audible. The repeated reflection that results in the persistence of sound is called reverberation. In an auditorium or a big hall, excessive reverberation is undesirable. To reduce reverberation, the roof and walls of the auditoriums are generally covered with sound – absorbent materials like compressed fibre board, rough plaster or draperies. The seat material is also chosen on the basis of their sound absorbent properties.

Ex 12.2) A person clapped his hands near a cliff and heard the echo after 5 s. What is the distance of the cliff from the person if the                 speed of the sound, v is taken as 346 m s^–1? 

Sol: Given, Speed of sound, v = 346 m s^–1

Time taken for hearing the echo, t = 5 s

Distance travelled by the sound = v × t = 346 m s^–1 × 5 s = 1730 m

In 5 s sound has to travel twice the distance between the cliff and the person.
Hence, the distance between the cliff and the person = 1730 m÷2 = 865 m.

22. Uses of Multiple Reflection of sound–

• Megaphones or horns, trumpet etc. are designed to send sound in a particular direction without spreading it in all direction. Multiple reflections take place in a tube followed by a conical opening to guide most of the sound waves in forward direction towards the audience.
• Stethoscope is a medical instrument used for listening to sounds produced with in the body mainly heart and lungs.
• The ceilings of concert halls, cinema halls etc. are curved so that sound after reflection reaches all corners of the hall.

23. Range of hearing – The audible range of sound for human beings is from 20 Hz to 20,000 Hz. Children under the age of 5 and some animals like dogs can hear upto 25 kHz. As people grow older their ears become less sensitive to higher frequencies.

26. Infrasonic – Sounds below the frequency of 20 Hz is called infrasonic. Rhinoceros communicate with each other at frequencies as low as 5 Hz. Whales and elephants also produce sounds in infrasonic range.
    It is observed that some animals become disturb before an earthquake. The earthquakes produce low frequency sound before the main shock waves begin to alert the animals.
27. Ultrasonic – Frequencies higher than 20 kHz are called ultrasonic waves. Dolphins, bats and porpoises produce ultrasounds. Moths of certain families have very sensitive hearing equipment. These moths can hear the ultrasounds produced by bats to avoid their capture by the bats. Rats also play games by producing ultrasonic waves.
28. Applications of Ultrasound –

• Ultrasounds can travel along the well-developed paths even in the presence of obstacles. It is therefore used to clean parts located in hard to reach places. For example, spiral tube, odd shaped parts etc. Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution. Due to high frequency, the particles dirt, grease etc get detached and drop out.
• Ultrasound can also be used to detect cracks and flaws in the metal blocks. Huge metal blocks that are used in construction industry, if cracked can reduce the strength of the structure. Ultrasonic waves are allowed to pass through the metal blocks and detectors are used to detect the transmitted waves if there is a crack in the metal block, the ultrasound will get reflected back indicating the defect in the block.
• Ultrasounds are also used in medical diagnosis. It is used take images of various parts of heart. This technique is called echocardiography.
• Ultrasound scanner is an instrument used to get the images of internal organs such as liver, kidney etc. In this technique ultrasound travels through various organs and is reflected from a region where there is a change in the tissue density. These waves are then used to generate images by converting into electrical signals. These images then can be printed on a film. This is called ultrasonography.
• Ultrasonography is also used during pregnancy to detect any congenial defects and growth abnormalities in the foetus.
• Ultrasound may be employed to break small stones formed in the kidneys into fine grains which later get flushed out with urine.

 

27. SONAR – The acronym SONAR stands for SOund  NAvigation and Ranging. SONAR is a device that uses the ultrasonic waves to measure the distance, direction and speed of underwater objects.

• SONAR consists of a transmitter and a detector installed in a boat or ship. The transmitter produces and transmits ultrasonic waves which travel through water and get reflected after striking the object and is sensed by the detector. The detector converts the ultrasonic waves to electrical signals. Which are then appropriately interpreted.
• The distance between the object and the ship is calculated by using the formula               2d = v × t
• Where d is the distance between the object and the ship, v is the velocity of sound through sea water and t is the time interval between the transmission and the reception of the ultrasonic sound
• The above method is called echo ranging.

28. Uses of echo ranging / SONAR–

• It is used to determine the depth of the sea
• It is also used to locate underwater hills, valleys, submarines, ice bergs, sunken ships etc.

29. How do bats catch their prey?

    Bats search out their prey and fly dark night by emitting and detecting high pitched ultrasonic squeaks, which are reflected from the obstacles or prey and returns to the bat’s ear. The nature of reflection tells the bat where the obstacle or prey is and what it is like.

• Porpoises also use ultrasounds for navigation and location of food in the dark.

 

The French Revolution: A Turning Point in History

The French Revolution, one of the most significant events in modern history, marked a radical shift in the political, social, and economic landscape of France. It ignited a flame of change that spread across Europe and influenced subsequent revolutions throughout the world. In this article, we will delve into the causes, key events, and lasting impact of the French Revolution.

Introduction

The French Revolution, which took place from 1789 to 1799, was a period of intense political and social upheaval in France. It was characterized by a series of profound transformations that challenged the existing monarchy and aristocracy, ultimately leading to the establishment of a democratic government.

Background of the French Revolution

To understand the French Revolution, it is essential to explore the prevailing conditions in France leading up to the upheaval. In the 18th century, France was an absolute monarchy under the rule of King Louis XVI. The country was burdened with significant economic challenges, social inequality, and a rigid class system.

Causes of the French Revolution

The French Revolution was the culmination of various factors that had been brewing for years. Several key causes contributed to the explosive nature of the revolution.

Economic factors

France was plagued by economic troubles, including a mounting national debt, inflation, and a regressive taxation system that burdened the common people while exempting the nobility and clergy. The financial crisis further exacerbated the existing social tensions.

Social inequality

French society was divided into three estates: the clergy, the nobility, and the commoners. The first two estates enjoyed numerous privileges and held significant power, while the third estate, comprising the majority of the population, bore the brunt of heavy taxation and lacked political representation.

Political unrest

The absolute rule of the monarchy and its resistance to reform efforts created widespread discontent among the people. Enlightenment ideas emphasizing individual rights, liberty, and equality began to gain traction, inspiring calls for political change and challenging the established order.

Key Events of the French Revolution

The French Revolution unfolded through a series of pivotal events that shaped its trajectory and outcomes. These events shook the foundations of the old regime and set the stage for the birth of a new era.

Estates-General and Tennis Court Oath

In May 1789, the Estates-General, an assembly representing the three estates, was convened to address the country’s financial crisis. Frustrated with the unequal representation and lack of power, the third estate declared itself the National Assembly. They took the famous Tennis Court Oath, pledging not to disband until a constitution was established.

Storming of the Bastille

On July 14, 1789, the disgruntled citizens of Paris stormed the Bastille, a symbol of royal authority. This event marked a significant turning point and came to symbolize the overthrow of tyranny.

 

Rise of the Jacobin Club

The Jacobin Club, a political club formed in 1789, played a crucial role in the radicalization of the revolution. Led by figures such as Maximilien Robespierre, the Jacobins pushed for more extensive political and social reforms, promoting ideas of popular sovereignty and republicanism.

 

Reign of Terror

The period known as the Reign of Terror, which lasted from 1793 to 1794, was characterized by intense political repression and violence. Robespierre and the Committee of Public Safety sought to suppress counter-revolutionary forces, leading to mass executions and a climate of fear.

 

 

Rise of Napoleon Bonaparte

Amidst the chaos and instability, Napoleon Bonaparte emerged as a military leader and eventually seized power in a coup d’état in 1799. His rise marked the end of the revolutionary period and the beginning of a new era in French history.

 

Impact of the French Revolution

The French Revolution had far-reaching consequences, both within France and globally. Its impact extended beyond political boundaries and reshaped societies and ideologies.

Spread of revolutionary ideas

The French Revolution’s ideals of liberty, equality, and fraternity spread across Europe, inspiring and influencing subsequent revolutions and movements for independence. It challenged the prevailing systems of governance and laid the groundwork for modern democratic principles.

Abolition of feudalism

The French Revolution marked the end of the feudal system in France. Feudal privileges were abolished, and the concept of social hierarchy based on birthright was challenged. This led to a more egalitarian society where merit and individual rights gained prominence.

Rise of nationalism

The French Revolution fueled the growth of nationalistic sentiments, emphasizing the importance of the nation as a collective entity. It fostered a sense of identity and solidarity among the French people and served as a model for other nationalist movements around the world.

Influence on other revolutions

The French Revolution’s impact extended beyond Europe. It influenced revolutionary movements in Latin America, inspiring independence movements against colonial powers. The ideals of the French Revolution resonated with oppressed peoples globally, sparking a wave of anti-colonial and anti-imperialist struggles.

Conclusion

The French Revolution stands as a pivotal moment in history, marking a significant shift towards democratic governance, social equality, and the rise of nationalism. It challenged the status quo, inspired generations, and continues to be studied and debated to this day. The revolution’s legacy serves as a reminder of the power of ideas and the potential for radical change in the face of injustice.