Saturday, July 30, 2011

NCERT CBSE Class 7th Science Chapter 9 : Soil

What is soil?
Soil is the crust part of the earth. It is mainly the mixture of rock particles and humus.

How will you say that the soil is one of the most important natural resources

  Soil is one of the most important natural resources because
- It supports the growth of plants by holding the roots firmly and supplying water and nutrients.
- It is the home for many organisms.
- Soil is essential for agriculture. Agriculture provides food, clothing and shelter for all.
- Soil is thus an inseparable part of our life.

What are the factors which affect the soil?

Wind, rainfall, temperature, light and humidity are the factors which affect the soil soil profile and bring changes in the soil structure.

What do you mean by soil profile?

A vertical section through different layers of the soil is called the soil profile.

What are horizons?

Each layer of soil differs in feel (texture), colour, depth and chemical composition.
These layers are called horizons.

What factors are used to differentiate various layers of soil?

The layers of soil are different from each other in respect to their texture, colour, depth, particle size and chemical composition.

Describe the different layers in soil profile.

(a) Different layers of the soil are referred to as horizons.The uppermost layer, the top soil, also known as A-horizon is generally dark in color and fertile as it is rich in humus and minerals. This layer is generally soft, porous and can retain more water. This provides shelter for many living organisms such as worms, rodents, moles and beetles. The roots of small plants are embedded entirely in the topsoil.

(b) The next layer, middle layer called B-horizon has a lesser amount of humus but more of minerals. This layer is generally harder and more compact.

(c) The third layer is the C-horizon which is made up of small lumps of rocks with cracks and crevices.

(d) Below this layer is the bedrock, which is hard and difficult to dig with a spade. Water can be held in the tiny gaps.

What is humus?

A non living organic matter formed from remains of dead and decay  plants and animal by the activity of micro organism present in soil.

Why is top soil known as the habitat of many living organisms?

Soil is the habitat for many living organisms, like bacteria, fungi, protozoan and earthworms as it contains large amounts of nutrients. Therefore top soil is called the habitat of many living organisms.

Why Upper most layers in a soil profile is described as most productive

In the soil profile, Horizon – A, also known as Topsoil is best suited for the plant growth.
As we know that availability of nutrients and water in soil helps to determine the productivity of soil. Top soil is it is rich in humus minerals along with water Therefore Top soil is considered as more productive.

How soil is formed?

The soil is formed by the breaking down of rocks by the action of wind, water and climate. This process is called weathering.

There are two different types of weathering.  Physical weathering  and chemical weathering.

Mechanical (physical) weathering is the breakdown of rock into smaller particles due to such factors as as freezing and thawing, release of pressure, water absorption, salt crystal formation, land mass uplift, expansion and contraction from the sun or fire, plant root growth, actions of animals, abrasion, or other means that do not directly affect the rock's chemistry.

Chemical weathering is the dissolution, carbonation, oxidation, or hydrolysis of rock and mineral by chemical means only, mostly from reactions with water or the acids contained in rainwater. Other materials are formed in the process. Warm, tropical climates are ideal environments for chemical weathering to take place as the chemical reactions are quickened by the bountiful rain and warm temperatures.

What is the similarity between chemical and mechanical weathering?

They both reduce the size of a rock body

At what factors nature of soil depend on?

The nature of any soil depends upon the rocks from which it has been formed and the type of vegetation that grows in it.

Plants help the development of the soil. How?

The plants attract animals, and when the animals die, their bodies decay. Decaying matter makes the soil thick and rich. This continues until the soil is fully formed. The soil then supports many different plants.

The soil is classified on the basis of the proportion of particles of various sizes. How?

If soil contains greater proportion of big particles it is called sandy soil.
If the proportion of fine particles is relatively higher, then it is called clayey soil.
If the amount of large and fine particles is about the same, then the soil is called loamy.
Thus, the soil can be classified as sandy, clayey and loamy.

Soil particles size is an important factor to determine the property of soil. Explain.

 Different particles of soil have different sizes which affect its properties such as:

(a) Sand particles are quite large and having  large spaces between them. These spaces are filled with air. Water can drain quickly through these spaces. So, sandy soils tend to be light, well aerated and rather dry.

(b) Clay particles, being much smaller, pack tightly together, leaving little space for air. So, clay soils have little air. But they are heavy as they hold more water than the sandy soils.

(c) Loamy soil is a mixture of sand, clay and another type of soil particle known as silt. The size of the silt particles is between those of sand and clay. The loamy soil also has humus in it. It has the right water holding capacity for the growth of plants.

Why loamy soil is known as best for growing plants?

The loamy soil has adequate  humus mixed in it. It has the right water holding capacity for the growth of plants. So loamy soil is known as  best for growing plants

What is silt? It is a component of which type of soil?
Silt is the soil present as deposits in riverbeds. It is formed by the weathering of rocks in the mountains and flows into the rivers. It is a component of loamy soil which is considered most suitable for growth of plants.

What is percolation of water? How it is different for different types of soil?

The gravity flow of groundwater through the pore spaces in rock or soil is called percolation of water. Percolation rate of water is different in different types of soil. It is highest in the sandy soil and least in the clayey soil.

What are the factors help us to determine the various types of vegetation and crops that might grow in any region?

The climatic factors, as well as the components of soil, determine the various types of vegetation and crops that might grow in any region

How does moisture affect the fertility of the soil?

The ability of a soil to hold water is called soil moisture. Soil moisture impacts the distribution and growth of vegetation, soil aeration, soil microbial activity, soil erosion, concentration of toxic substances and the movement of nutrients in the soil to the roots, thus affect fertility of soil. For example, clayey and loamy soils both have good water retaining  capacity. Crops such as wheat are grown in the fine clayey soils, because they are rich in humus and are very fertile.

What are the main agents of weathering ?

The main agents of weathering are :-
1. Temperature: Temperature changes that cause the rock surface to break apart
2. Frost:  Ice expand and produce pressure , causing the crevices in rock to open
3. Water: - Continuous movement of rain water causes braking down of rock particles into fine particles
4. Air : Wind blow across rock surface and carry minute particle and form layer
5. Living organism : - Lichen grow on the surface of rocks and produce acid which corrode the rocky surface .Weathering by living organism is called biological weathering.

How is clayey soil useful for crops?

Clayey  soil having a good capacity to retain water. It is also  rich in organic matter So best suitable for growing cereals like wheat, And gram

What are the causes of soil erosion?

Soil erosion is mainly caused by rain, wind, flooding, overgrazing, and deforestation. Erosion of soil is more severe in areas of little or no surface vegetation, such as desert or bare lands

How can soil erosion be prevented?

There are many ways to prevent soil erosion
(i) By planting more trees and increasing the vegetation cover.
(ii)By prevented Cutting of trees and deforestation and taking efforts to increase the green areas.
(iii)By maintaining soil in its natural condition by using less manure or by crop rotation
(iv)By arranging proper irrigation

What are the different types of soils found in india?

Late rite Soils :- This typical soil is found in those regions which receive heavy rainfall. This soil is poor in lime content and hence it is more acidic. This soil contains least moisture content.It is basically red in colour because of the presence of iron oxides. It is more popular in the coastal regions of Ratnagiri District and Malabar.
Black Soil :- It is black in colour due to presence of salt and large amount of humus . This soil becomes sticky when is wet. It does not contain adequate nitrogen but it contains sufficient phosphorous required for the growth of the plants.It is generally found in hilly areas.

Red and Yellow Soils : Red and yellow soils are found in areas, which receive low rainfall. They contain huge concentration of iron oxides that are responsible for giving the reddish or yellow colour.

Alluvial Soils : Alluvial Soils are mainly found in the plains of northern India. These soils have low phosphorous and nitrogen content and found in the north western regions of the country

Mountain Soils : Mountain soils are considered as a significant variety of soil in the Himalayan region of the country. They are mainly found in dry and cold district in the northern region of India.

Central Teacher Eligibility Test ( CTET) overview

The results of the first Central Teacher Eligibility Test ( CTET)) conducted by CBSE for recruitment of teachers to Central Government schools, were declared on Tuesday with 97,919 candidates clearing it.

Of the total 79,4080 candidates registered for the test, 71,5050 had sat for the exam held on June 26. The test was conducted in 1,178 centres and 81 cities across the country and two cities abroad

Friday, July 29, 2011

Class 7th Motion and Time Solved Questions

Question:1. What is motion?

Answer: Motion is a change in the position of an object with time.

Question:2. What is rest ?

Answer: When a body do not change its position with it said to be in rest

Question:3. How can you say that motion and rest are relative ?

Answer: We have observed that the position of stars and planets change while you remain stationary. In 

reality the earth is moving too. Thus, an object which appears to be at rest, may actually be in motion. 
Therefore, motion and rest are relative terms.

Question:4. What is  rectilinear motion?

Answer: The motion of an object along a straight line is called rectilinear motion. For example the motion of a 

vehicle on a straight road, march-past of soldiers in a parade or the falling of a stone.

Question:5. What is circular motion?

Answer: Motion of an object in a circular path is called circular motion eg. Motion of the hands of a clock.

Question:6. What is periodic motion?

Answer: When an object repeats its motion after some time. This type of motion is called periodic motion. 

Eg. Motion of a pendulum , motion of a child on a swing, motion of the strings of a guitar.

Question:7. Define non-uniform motion?

If the speed of an object keeps changing in equal interval of time , while moving along a straight line, its 

motion is said to be non-uniform.

Question:8. What is oscillatory motion?

Answer: The to and fro motion of an object from the position of rest is called  an oscillatory motion.

Question:9. Give an example when objects undergo combinations of different types of motion?

Answer: The motion of a ball on the ground. Here the ball is rolling on the ground and rotating as well as 

moving forward on the ground. Thus, the ball undergoes a rectilinear motion as well as rotational motion.

Question:10. What is speed of an object?

Answer: The distance covered by an object in a unit time as the speed of the object. the basic unit of speed 

is m/s. Of course, it could also be expressed in other units such as m/min or km/h.

Question:11. What is the difference between uniform and non uniform motion ?

Answer: Uniform motion

An object moving along a straight line with a constant speed is said to be in uniform motion.

In this case, the average speed is the same as the actual speed.

Non-uniform motion

If the speed of an object moving along a straight line keeps changing, its motion is said to be non-uniform. In 

this case, the average speed is different fron the actual speed.

Question:12. What is time?

The interval between two events is called time. Example: The time between one sunrise and the next was 

called a day. Clocks or watches are the most common time measuring devices. The basic unit of time is a 
second. Its symbol is s. Larger units of time are minutes (min) and hours (h).

Question:13. What is simple pendulum?

Answer: A simple pendulum consists of a small metallic ball or a piece of stone suspended from a rigid stand 

by a thread .The metallic ball is called the bob of the pendulum.

Question:14.What is oscillation of a pendulum?

Answer: One complete to and fro motion of a pendulum from rest position is called one oscillation.

The time taken by the pendulum to complete one oscillation is called its time period. It is only depending on 

the length of the string of pendulum.

Question:15. What are the different types of motion? 

Answer: Translatory Motion  :  -  In translatory motion the particle moves from one point in space to 

another. This motion may be along a straight line or along a curved path.  

Rectilinear motion   :  Motion along a straight line is called rectilinear motion.   Example: A car moving on a 

straight road

Curvilinear motion  :  Motion along a curved path is called curvilinear motion.Example: A car negotiating a 


Rotatory Motion :  In rotatory motion, the particles of the body describe concentric circles about the axis of 


Vibratory Motion In vibratory motion the particles move to and fro about a fixed point.  Example   Simple Pendulum

Question:15. Who made the pendulum clock? 

Answer: The first pendulum clock, invented by Christiaan Huygens in 1656.Huygens was inspired by investigations of pendulums by Galileo Galilei beginning around 1602.

Wednesday, July 27, 2011

National Talent Search Exam (NTSE) 2012

National Talent Search Exam: 2012

National Talent Search Scheme is a flagship activity of the NCERT started in the year 1963. The purpose of the scheme was to identify talented students and nurture their talent.

The NCERT conducts the National Talent Search Examination for students studying in Class VIII only.

Scholarships: On the basis of the examination conducted, 1000 scholarships will be awarded for each group of students appearing for Class VIII examinations. The amount of scholarship will be Rs.500/- per month as per NTS rules.

Reservation: 15% scholarships will be reserved for students belonging to the SC category, 7.5% scholarships for students belonging to the ST category and 3% for Physically Challenged Group of Students.

Selection: There will be two-stage selection process for award of scholarship. For Stage-I, selection will be done by States/UTs through a written examination. Students who qualify Stage I will be eligible to appear for Stage II examination conducted by NCERT. The States/UTs will also conduct the selection test for National Means-cum-Merit Scholarship Scheme along with the Stage-I written examination for NTS.

Tuesday, July 26, 2011

CBSE Class-7 Science Heat and temperature

CBSE Class-7 Science Heat and temperature By 
Questions: Fill in the blanks :
(a) The hotness of an object is determined by its temperature.

(b) Temperature of boiling water cannot be measured by a clinical thermometer.

(c) Temperature is measured in degree

(d) No medium is required for transfer of heat by the process of Radiation.

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of  conduction.

(f )
Clothes of dark colours absorb heat better than clothes of light colours.

Questions: Match the following :
(i) Land breeze blows during  à night
(ii) Sea breeze blows during-àday
(iii) Dark coloured clothes are preferred during à winter
(iv) Light coloured clothes are preferred during-àsummer

Questions: What is heat?

Heat is a form of energy, entry or exit of which correspondingly increases or decreases internal energy of a body when no work is done on the body or by the body.

Questions: What is temperature?
A reliable measure of the hotness of an object is its temperature. Temperature is measured by a device called  thermometer.

Questions:What is clinical thermometer?

The thermometer that measures our body temperature is called a clinical thermometer
A clinical thermometer consists of a long, narrow, uniform glass tube. It has a bulb at one end. This bulb contains mercury.

Questions: Why clinical thermometer ranging 35oC to 42oC.?

The normal temperature of human body is 37°C.The temperature of human  body normally does not go below 35oC or above 42oC. That is the reason that this a clinical thermometer has the range 35oC to 42oC.

Questions: What is the use of the m a x i m u m - m i n i m u m thermometer?

Different types of thermometers are used for different purposes. The maximum and minimum
temperatures of the previous day, reported in weather reports, are measured by a  thermometer called the m a x i m u m - m i n i m u m thermometer.

Questions: What is the range of a laboratory thermometer?

The range of a laboratory thermometer is generally from –10°C to 110°C

Questions: Why does the mercury not fall or rise in a clinical thermometer when taken out of the mouth?

Kink prevents mercury level from falling on its own.

Questions: What is conduction?

Heat flows from a hotter object to a colder object. The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.

Questions: Why conduction is only possible in solids

In solids, generally, the heat is transferred by the process of conduction because particles of solids are closely packed and heat is transferred from the hotter end to the colder end of an object.

Questions: What are conductor and insulators?

The materials which allow heat to pass through them easily are conductors of heat. For examples, aluminum, iron and copper

The materials which do not allow heat to pass through them easily are poor conductors of heat known as insulators such as plastic and wood.

Questions: Explain how water heated by convection?

The water is  poor conductors of heat so do not heated by conduction.
When water is heated, the water became lighter. Hot water rises up. The cold water from the sides moves down towards the source of heat  This water also gets hot and rises and water from the sides moves down. This process continues till the whole water gets heated. This mode of heat transfer is known as convection

Questions: What is land and sea breeze explain?

During the day, the land gets heated faster than the water. The air over theland becomes hotter and rises up. The cooler air from the sea rushes in towards  the land to take its place. The warm air from the land moves towards the sea to complete the cycle. The air from the sea
is called the sea breeze.

At night  , The water cools down more slowly than the land. So, the cool air from the land moves towards the sea. This is called the land breeze

Questions: How does the heat from the sun reach us?

It cannot reach us by conduction or convection as there is no medium such as air in most part of the space between the earth and the sun. From the sun the heat comes to us by  another process known as radiation.

Radiation can take place whether a medium is present or  not.

Questions: In summer we prefer light-coloured clothes and in winter we usually wear dark-coloured clothes. Why

Dark surfaces absorb more heat and, therefore, we feel comfortable with dark coloured clothes
in the winter. Light coloured clothes reflect most of the heat that falls on them and, therefore, we feel more comfortable wearing them in the summer.

Questions: How Woolen clothes keep us warm in winter

Woollen clothes keep us warm during winter. It is so because wool is a poor conductor of heat and it has air trapped in between the fibres

Questions: Why one thick blanket  is less warm up than  two thin blankets joined together?

There ia  a layer of air in between the blankets..Since air is bad conductor of heat prevent body heat to escape out.

Questions: How is heat transferred in solids, liquids and gases?

The heat flows from a body at a higher temperature to a body at a lower temperature
In solids, generally, the heat is transferred by conduction. In liquids and gases the heat is transferred by convection. No medium is required for transfer of heat by radiation

Questions: Why we wear light cloths in summer?

Dark-coloured objects absorb radiation better than the light-coloured  objects. That is the reason we feel more comfortable in light-coloured clothes in the summer

Questions: What are the different thermometer scales?

Different thermometer scales

(a) The centigrade or Celsius scale: It is introduced by Celsius, is usually used in scientific laboratories. In this scale the lower fixed point or the ice-point is 0°C and the steam-point 100°C. The fundamental interval is divided in 100 equal parts; each part is called 1°C (one degree Celsius).

(b) The Fahrenheit scale: It is suggested by Gabriel Fahrenheit, is usually used in clinical and meteorological purposes. Here, the ice-point and the steam-point are correspondingly marked as 32°F and 212°F, and the fundamental interval is divided into 180 equal divisions. Each division is called one degree Fahrenheit. (1°F).

(c) Absolute scale or Kelvin scale: It is designed by Lord Kelvin, is used internationally in modern scientific world. In this scale the ice-point is marked 273K and the steam-point 373K, the fundamental interval is divided into100 equal divisions, like that in the Celsius scale. Each division is read as one degree absolute or one Kelvin (IK). In fact, Kelvin scale of temperature starts from the temperature corresponding to -273°C, taken as zero Kelvin 

Questions: What is the Relation between Celsius, Fahrenheit and Kelvin scales?

Since the range of temperature from ice-point to steam-point is equal in all the three scales, 100 centigrade degrees = (212 - 32) or 180 Fahrenheit degrees = (373 - 273) or 100 absolute degrees.
We consider three thermometers in the above three scales are dipped simultaneously in a liquid of certain temperature.
Let the temperatures recorded in the Celsius, Fahrenheit and Kelvin thermometers  respectively be C, F and K.    
Now it can be proved that  C / 5 = F- 32 / 9 = K- 273 /5

Questions: What is the unit of heat

Units of Heat
(a) C.G.S. unit of heat is Calorie.
(b) The M.K.S. or S.I. unit of heat is Joule

1 calorie equals 4.18 or 4.2 joules approximately.

Questions: The quantity of heat absorbed or given out by a substance during a thermal change depends on what factors?

The quantity of heat absorbed or given out by a substance during a thermal change depends on
(a) mass,
(b) difference of temperature and
(c) Specific heat of the material of the substance.

(a) Mass: A larger mass of a substance absorbs or gives out more heat than a smaller mass of it for a certain change of temperature. So, if 'H' be the quantity of heat absorbed or given out by a substance of mass 'm’ for a given change of temperature, H = m.

(b) Temperature: The heat absorbed or released by a certain quantity of a given substance increases or decreases accordingly as the difference between the initial and final temperatures is large and small. Thus, H= (T-t) where, (T-t) is the difference between the initial and the final temperatures of the body.

(c) Specific heat: This is a fundamental property of matter. An equal mass of different materials absorb or give out different quantities of heat, even if they are heated or cooled through the same range of temperature.This is also called specific heat capacity (abbreviated as SHC) in S.I. system.

Heat (H) absorbed or given out by body of mass (m) for rise or fall of temperature through t is given by H = mst. 

Questions: State similarities between the laboratory thermometer and the clinical thermometer

1. Laboratory thermometer and the clinical thermometer consist of a long, narrow, uniform glass tube.
2. Laboratory thermometer and the clinical thermometer have a bulb containing mercury at the end of the tube.
3. Laboratory thermometer and the clinical thermometer are marked with Celsius scale on the glass tube.

Questions: Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

In between the layers of cloths there is trapped air. As air is bad conductor of heat so the out side low temperature do not get transferred to body as well as prevent our body heat to escape out side. Hence more layers of cloths keep us warmer during cold winter.

Questions: In places of  hot climate it is advised that the outer walls of houses be painted white. Explain.

In places of  hot climate it is advised that the outer walls of houses be painted white because a light colour absorb very less radiant heat  and we feel comfortable inside such houses due to lower temperature inside house.

Questions: Why stainless steel cooking utensils  are usually provided with copper bottoms?