Current Affairs 9th Class

  Work and Energy   Chapter Overview  
  • Introduction
  • Definition of Work
  • Measurement of work done by a content force
  • Nature of work
  • Unit of work
  • Energy
  • Different forms of energy
  • Kinetic energy
  • Relation between kinetic energy and linear momentum
  • Potential energy
  • Definition of potential energy
  • Types of potential energy of a system
  • Potential energy of an object at a height
  • Transformation of energy
  • Conversion of potential energy into kinetic energy and then in electrical energy
  • Devices used to transform energy from one form to another
  • Law of conservation of energy
  • Power
  • Average in terms of energy
  • Power in terms of energy
  • Commercial unit of energy
 
  • Introduction
  • The concept of work is related to the concept of energy. The general ideas of work-energy can be applied to a wide range of phenomena in different fields of physics. In our daily life, any physical or mental activity is termed as work done. However, in physics, the meaning of work is entirely different. In this chapter, we shall discuss the difference between the term 'work' used in our daily life and the term "work" defined in physics. Work-energy approach is based on Newton's Laws and as such does not involve any new principles. Further, from a practical point of view, it is important to know not only the work done on a particle but also the rate at which it is being done.  
  • Definition of work
  • "Work is said to be done only when the force acting on a body produces motion in it, in the direction of the force applied. Factors on which work done depends (1) Magnitude of the force applied: More the force applied, the more is the work done provided the body is displaced. Work done (W) = Force applied (F) provided the body is displaced W = F   (2) Displacement of the body: Work done by the force on a body is directly proportional to he displacement of the body in the direction of force applied. Work done = Displacement of the body     Remember: No work is done if a body does not change its position on the application of force.  
  • Measurement of work done by a constant force
  • (a) When the body moves in the direction of the applied force OR When a constant force is applied in the horizontal direction When a force F acting on a body produces displacement s in it.   Fig.3.1.   Work done = Force x Displacement (in the direction of force) \[W=F\times s\] The work done on the block (or any other object) by a constant force is equal to the product of the magnitude of the more...

      Sound   Chapter overview  
    • Introduction
    • Production of sound
    • Wave
    • Medium
    • Propagation of sound
    • Classification of wave motion
    • Graphical representation of Longitudinal waves
    • Difference between Longitudinal and Transverse waves
    • Characteristics of a sound wave
    • Relation between wave speed, frequency and wavelength
    • Factors affecting the Loudness of sound
    • Difference between Musical sound and Noise
    • Speed of Sound
    • Shockwaves-Sonic boom
    • Echo
    • Reverberation
    • Uses of multiple reflection of sound
    • Range of Hearing (Audible Range)
    • Infrasenics or Infrasound
    • Ultrasonics or Ultrasound
    • Echolocation
     
  • Introduction
  • The five basic senses of human beings are sight, touch, taste, smell and hearing.       After sight, sound is the most important among our senses. It keeps us informed about our surroundings. Sound is a form of energy just like heat and light. We hear sounds from various sources of moving vehicles of televisions, people in our surroundings, machine and so on. Sound is a form of energy which produces a sensation of hearing in our ears. What is sound exactly? What are the characteristics of sound? What is the mechanism of creating and propagating sound? We will find the answers to these questions while we study this chapter.  
  • Production of Sound
  • Sound is produced when a body vibrates, i.e. sound is produced by vibrating bodies. The following experiments demonstrate this fact. See Article NCERT Activities 1.               
  • Wave
  • The movement of the disturbance through a medium due to the repeated periodic motion of the particles of the medium about their mean position is known as a wave. Wave motion is a type of motion in which energy is transferred from one region to another without the actual movement of molecules of the medium from one region to other.  
  • Medium
  • A substance or matter through which mechanical wave is transmitted is called medium. e.g. solid, liquid, gas etc. Mechanical wave: A mechanical wave is a periodic disturbance which requires material medium (solid, liquid, gas) for its propagation. Examples: Sound waves, water waves, seismic wave (known as waves produced by earthquake), waves produced in a stretched string, waves produced in a slinky. Electromagnetic waves (EM wave): Those waves which do not required any material medium like solid, liquid or gas for their propagation. They are called electromagnetic waves. e.g., light waves, radio waves.   Do You Know Sound wave travel in air at very low speed of 3-32 m/s at\[20{}^\circ C\]. But light waves travel at a very high speed of \[3\times {{10}^{8}}m/s\]in air.  
  • Propagation of Sound
  • A vibrating body produces sound. Now we shall study, how the sound travels from one dace to another place. When a body or an object vibrates, then the particles of the medium around the object are set into vibration. These particles do not move their equilibrium position but simply vibrate about their equilibrium positions. A particle of the more...

      Why Do We Fall ILL   Chapter Overview  
    • Introduction
    • Health and its failure
    • Disease and its causes
    • Types of disease
    • Infectious disease
    • Principles of treatment
    • Principles of prevention
    • Common microbial diseases and their prevention
    • Chapter at a Glance and Glossary
    • NCERT Activities
    • NCERT Intext Questions
    • NCERT Exercise
    • Other Important Questions
     
  • Introductions
  • Similarly, our body also has tissues, organs, and organ system. There are several specialized activities which keep on going all the time in these parts. For example, the heart beats to pump blood to all the body parts, the lungs breath to exchange gases, the kidneys filter the blood and separate urine and brain thinks. All these activities are interconnected. If our heart stops beating even for a while, the blood circulation will stop, thus the various parts of our body will not get nutrients and oxygen. This will adversely affect our body. Likewise, if our kidneys, stop filtering the blood, poisonous substances will accumulate in the body. Under such conditions, the brain will not be able to think properly. For all such interconnected activities, body requires energy and also requires regular supply of raw materials from outside the body. In other words, regular supply of food is necessary to the body so that essential components are provided to the cells for proper working of the tissues and organs. Anything that prevents proper functioning the cells, tissues and organs will lead to lack of proper activity of the body. In this chapter, we will try to understand health and disease in this perspective.  
  • Health and His Failure
  • The Significance of ‘Health' We use the term’ health' many times in different ways, for example, my grandmother's health is not good, A person remarks, "this is not a healthy attitude’' we may even talk about healthy climate of an area or a town. Then what is meant by the word health? When we consider the first statement the term health implies the idea of being well or functioning efficiently. For our grandmother, being able to walk around easily is being well and not being able to do so is being unwell' or 'unhealthy' Second statement implies the healthy attitude as being interested in some particular work with positive feeling while not being interested is called the 'opposite5. In third statement we are referring to the environmental conditions that are congenial for disease-free, happy life. Thus we can define health as "a state of being well enough to function physically, mentally and socially." The World Health Organisation (WHO), in 1948, has defined health as "a state of complete physical, mental and social well-being, and not merely an absence of disease or infirmity." In other words, WHO recognises three dimensions of health-   (a) Physical health: It refers to the normal structure of the body and more...

      Natural Resources   Chapter Overview  
    • Introduction
    • The breath of life: Air
    • Air pollution
    • Water: A Wonder Liquid
    • mineral Riches in the soil
    • Biogeochemical cycles
    • Greenhouse effect (Global warming)
    • Ozone layer
     
  • Introduction
  • Our earth is the only planet which has all the essential conditions required for the existence and survival of life. Life on earth is dependent on many factors such as an optimum temperature, water, food and air. The resources available on earth and the energy from the sun are necessary to meet the basic requirements of all life forms on the earth.   What are these resources on the Earth? All the varieties of substances that we get from Earth and nature to meet our basic needs are called Natural Resources. The word resource means a source of supplying a material generally held in reserve. These materials present in nature are air, water, soil, minerals petroleum, coal, animals and plants. These all are obtained from nature, thus, they are known as natural resources. Some of the related terms are as follows: (a) Lithosphere: It is outer solid crust of earth, also called land. Its upper thin weathered layer is known as soil. (b) Hydrosphere: It is water component of earth. 75% of the surface of the earth is covered by water, in form of oceans, rivers, lakes, ponds, dams etc. Another component of hydrosphere is underground water. (c) Atmosphere: The air that covers the whole of earth like a blanket is known as atmosphere. (d) Biosphere: Life forms are found where all of the three resources (i.e. lithosphere, hydrosphere and atmosphere) are found and interact with each-other. This life supporting zone of the earth ig known as Biosphere. Biosphere has two types of components biotic and abiotic. (i) Biotic components of biosphere are the living things. Various micro-organisms, plants, and animals form the biotic components of biosphere. (ii) Abiotic components of biosphere are the non-living things. Air, water, soil, temperature, minerals, metals etc. form the abiotic components of the biosphere. Both the types of components provide resources to meet the basic requirements of life forms. However the energy required for sustaining life is ultimately obtained from the sun.                   
    They can replenish themselves by quick recycling and replacement within a reasonable time. They cannot replenish more...
      Improvement in Food Resources   Chapter Overview  
    • Introduction
    • Improvement in crop yields
    • Crop variety improvement
    • Crop production management
    • Crop protection management
    • Fish production (Pisciculture)
    • Bee-Keeping (Apiculture)
    • Chapter at a Glance and Glossary
     
  • Introduction
  • We know that all living organisms need food to get energy and nutrients like protein, carbohydrates, fats, vitamins and minerals. All these nutrients are required for maintenance of our body, development, growth, proper health and sustenance. These nutrients are provided by both plants and animals. It means we are directly or indirectly dependent on agriculture and animal husbandry. Hence the improvement of agriculture as well as of animals has always been Inevitable since time immemorial. But even then, it is natural to think over some burning questions Like, Can the current levels of production be sufficient for us? Why it is necessary to improve the plants and animals? How can we meet with the current demands of production? The reasons of all these questions lie in the following facts:  
  • Population Explosion: Our country is second largest in population in the world with about 1.2 billion people. The problem is day by day aggravating by the continuous rise in population. At this rate it is expected that Indian population may reach around 1-3 billion by the end of 2020. For supplying the food to the ever increasing population of our country, it is necessary that we increase the production of agricultural and animal products because it is estimated that in future we will need more than a quarter of a billion tonnes of grains every year to feed our people. The increase in food yield can be done either by farming on more land or by improving the production efficiency through some modem scientific practices.
  • The first mode of increasing the farming land, is not easily possible in our thickly populated country. Hence, the second point is the only best option with us.  
  • Farming Revolution: So far, by applying the modem scientific methods, we have supplemented our demand of the food to some extent. Like green revolution to increase food grain production and white revolution to better and more efficient use as well as availability of milk. Some more revolutions like blue revolution (enhanced fish and silver revolution (increased poultry production) have also helped to compensate with the increasing demand of food production.
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      Tissues   Chapter Overview  
    • Introduction
    • Division of Labour
    • Plant and Animal Tissues are different
    • Plant tissues
    • Meristem tic tissue
    • Permanent tissue
    • Animal tissue
    • Epithelial tissue
    • muscular tissue
    • Connective tissues
    • Nervous tissue
     
  • Introduction
  • You have studied in the previous chapter that all living organisms are made up of cells. They are either unicellular (e.g. diatoms, bacteria, yeast protozoans etc.), or multicellular (e.g.) frog, earthworm, dog, man, mango tree, money plant, peepal etc). Most of cells are specialized to carry out different functions. Each specialised function is taken up by a different groups of cells. Since these cells carry out only a particular function. For instance in human beings, muscle cells combine together to perform contraction and relaxation to cause movements, nerve cells cord in ate to carry messages; blood cells and plasma to transport oxygen, carbon dioxide, food, hormones and waste materials, and so on. Similarly in plants, cells combine to perform specific functions such as transportation of food and water from one part to the other; synthesis of food material, storage of reserve foods, etc. Thus a kind of division of labour exists in the cells of multicellular organisms to perform specific functions.  
  • Division of Labour
  • The body of multicellular organisms is made up of organ systems, organ systems are made up of organs, organs are composed of tissues and tissues are composed of cells. Most of these cells are specialised to carry out only few functions efficiently. These functions are taken up by different groups of cells. Thus, we can say that there is a division of labour in the multicellular organisms. "Division of labour refers to the distribution of different functions among different parts of the body of organism which get specialized for the particular function." Cell division and cell differentiation lead to the development of specific organs, consisting of specific groups of cells to perform specific functions in the body. Moreover, the organs are also made up of different groups of cells on the basis of their functions. A particular function, inside an organ is performed by group of specialised cells which lie at a definite site in the body. The cluster of cells specially positioned and designed to perform a particular function efficiently is known as tissue.      
    Green revolution Cereal grain production
    Tissue: A group of similar or dissimilar cells that perform a common function and have a common origin, is known as Tissue
    more...

       The Fundamental Unit of Life   Chapter Overview  
    • Introduction
    • What are living organisms made up of?
    • Discovery of cell
    • Cell theory
    • Structure of cell
    • Plasma Membrane or Cell Membrane
    • Osmotic Solutions
    • Endocytosis and exocytosis
    • Cell wall
    • Nucleus
    • Cytoplasm
    • Cytosol
    • Cell Organelles
    • Endoplasmic Reticulum (ER)
    • Golgi Apparatus
    • Lysosomes
    • Plastids
    • Plastids
    • Vacuoles
    • Ribosomes
     
  • Introduction
  • All the living organisms which we see in our surrounding are essentially complex structures made up of numerous coordinated compartments usually known as cells. The cell is the fundamental structural and physiological unit of living organisms. Unicellular organisms consist of just one cell while multicellular organisms consist of several cells, which are specialised to perform distinct functions. A unicellular organism can perform its all metabolic activities which a multicellular organism can. The cell contains all the structures and molecular constituents needed for life.  
  • What are living Organisms Made up of?
  • We can compare a cell with a brick. Just as a building is made up of bricks, the body of a plant or an animal is made up of cells, i.e. all living organisms show cellular organisation, Some organisms such as Amoeba, Paramecium, Euglena, Bacteria etc. are made up of only single cell, hence are called unicellular or a cellular. There are large number of other organisms which are made up of millions of cells and are known as multicellular. All cells, whether the exist as unicellular organisms or as part of multicellular organisms demonstrate certain similar basic functions such as nutrition, respiration excretion etc. which are essential for their survival.  
  • Discovery of Cell
  • The history of the cell began with the invention of a microscope by the Dutch scientist Anton Van Leeuwenhoek (1632-1723) who observed the living cells of bacteria, Euglena sperms, eggs and blood corpuscles of invertebrates in 1683. Robert Hooke (1635-1703) an English scientist, invented a primitive microscope by using lenses for achieving greater magnification. In such a microscope, the object to be seen was   Fig.: 3.1. Primitive microscope of Robert Hooke    Fig.: 5-2. Cells as seen by Robert Hooke   placed on a stage below and light coming from an oil flame was thrown on it by a convex mirror. While studying a slice of cork Robert Hooke observed a honeycomb like pattern under his microscope in 1665. He coined the term cell (cellulae), the Latin word, which means "a little room". He published his findings in Micrographic in London in 1665. Robert Brown (1773-1858) a Scottish botanist, discovered a little sphere like structure in the cells of the orchid root in 1831. Later he named it Nucleus. The gel like substance present in all the living cells was termed protoplasm by Hugo Von Mohl (1838) and Joharines more...

       Structure of the Atom   Chapter Overview  
    • Introduction
    • Thomson’s Model of Atom
    • Rutherford’s Model of Atom
    • Bohr’s Model of Atom
    • Discovery of Neutron
    • Atomic Number and Mass Number
    • Electronic configuration (Bohr-Bury Sheme)
    • Concept of Valency
    • Isotopes
    • Isobars
     
  • Introduction
  • On the basis of experimental observations, different models have been proposed for the structure of an atom.  
  • Thomson’s model of Atom
  • According to Thomson's model, atoms can be considered as a large sphere of uniform positive charge with a number of small negatively charged electrons scattered throughout it. This model was called as plum pudding model. The electrons present the plums in the pudding made of negative charge. This model is similar to of watermelon in which the pulp represents the positive charge and positive charge the seeds denote the electrons,                              Fig. 2.1. Thomson?s plum-pudding model
  • Rutherford’s Model of Atom
  • (Alpha Particle Scattering Experiment) Rutherford in 1911 performed an experiment which led to the downfall of Thomson's model According to Rutherford's model:
  • An atom contains a dense and positively charged region located at its centre, it was called as nucleus.
  • All the positive charge of an atom and most of its mass was contained in the nucleus.
  • The rest of an atom must be empty space which contains the much smaller and negatively charged electrons.
  • Total negative charge on the electrons is equal to the total positive charge on the nucleus, so that atom on the whole is electrically neutral.
  • On the basis of the proposed model, the experimental observations in the scattering experiment. The a-particles passing through the atom in the region of the electrons would pass straight without any deflection. Only those particles that come in close vicinity of the positively charged nucleus get deviated from their path. Very few \[\alpha \]-particles, those that collide with the nucleus, would face a rebound.                                                              
  • Bohr’s Model of Atom
  • In 1913 Niels Bohr, a student of Rutherford proposed a model to account for the shortcomings of Rutherford's model. Bohr's model can be understood in terms of two postulates proposed by him. The postulates are:                                                                  Postulate 1. The electrons move in definite circular paths of fixed energy around a central nucleus.                                                                                 Fig. 4.1. Illustration showing different orbits or the energy levels of fixed energy in an atom according to Bohr?s model   Postulate 2. The electron more...

      Atoms and Molecules   Chapter Overview
    • Introduction.
    • Laws of Chemical Combination.
    • Dalton’s Atomic Theory
    • Atom
    • Modern Day Symbols of Atoms of Different Elements
    • Atomic Mass
    • What is a molecule
    • Molecular formulae
    • Ion
    • Ionic compounds
    • Writing chemical formula of compounds
    • Relation between molecular formula and empirical formula
    • Valency
    • Formula of Ionic Compounds
    • Molecular Mass.
    • Percentage Composition of a Compounds
    • Mole Concept
    • Molar Mass
    • Gram-atomic Mass
     
  • Introduction
  • Around 500 B.C. an Indian philosopher Maharishi Kanda, said in his Darshan that if we go on dividing matter, we shall get smaller and smaller particles. A stage would come beyond which further division will not be possible. He named these particles as TAJRMANLT. This concept was further elaborated by another Indian philosopher, Pakudha Katya an. Katya an said, these particles normally exist in a combined form which gives us various forms of matter. Around the same era, sin ancient Greek philosopher Democritus (460 – 370 B.C.) and Leucippus suggested that if we go on dividing matter, a stage will came when further division of particles will not be possible. Democritus called these individual particles 'atoms' (which means indivisible). These ideas were based on philosophical considerations. In this chapter, we shall study about atom and molecules and related aspects, like atomic and molecular masses, mole concept and molar masses. We shall also learn how to write chemical formula of a compound.                                                                
  • Laws of Chemical Combinations
  • There are two main laws of chemical combinations:                             (i)  Law of conservation of mass,                                                     (ii) Law of definite or constant proportions.                                            Lavoisier gave the Law of Conservation of Mass as:                                  In every chemical reaction, total masses of all the reactants is equal to the masses of all the products.          \[\Rightarrow \]Total mass of the substances before the reaction = Total mass of the substances after the reaction For example, in the reaction of hydrogen \[({{H}_{2}})\]and chlorine \[(C{{l}_{2}})\]represented. Here 2g of \[{{H}_{2}}\] reacts with 71g of \[C{{l}_{2}}\]to give 73 g of HCl.   more...
      Is Matter Around Us Pure   Chapter Overview  
    • Introduction
    • Elements and Compounds
    • Mixture
    • Solution
    • Saturated solution
    • Supersaturated solution
    • Unsaturated solution
    • Solubility
    • Colloidal solution
    • Colloidal solution
    • Brownian motion
    • Tyndall effect
    • Electrophoresis
    • Separation of mixtures
    • Chromatography
    • Types of Chromatography
    • Distillation
    • Fractional distillation
    • Crystallization
    • Water purification in water works
    • Separation based on magnetic properties
    • Physical and chemical change
     
  • Introduction
  •   Matter around us is of two types: (i) Pure substances (ii) Mixture. In this chapter we will study about mixtures and pure substances. Initially, we will discuss about elements and compounds.  
  • Elements And Compounds
  •   A chemical element is a pure substance and it consists of one type of atom distinguished by its atomic number. Examples of some elements are: helium, carbon, iron, gold, silver, copper, aluminium, hydrogen, oxygen, nitrogen, sulphur, chlorine, iodine, uranium and plutonium.   Our body is also composed of elements but the composition of elements in human body is very much different from that of the Earth's crust, as it can be seen from Table 2.1 given below:       Table 2.1 Elements in Earth’s Crust and Human Body    
      \[{{H}_{2}}\]+ \[C{{l}_{2}}\]\[\to \] \[2HCl\]
    Molecular mass
      S. No.     Elements   Percentage by mass  
    Earth's crust Human body
    more...


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