Current Affairs 7th Class

Acids, Bases and Salts   Acids Acids are found in small amounts in nature. For example, acids are present in things that we eat such as lemon and orange contains citric acid, tomato contains oxalic acid, vinegar contains acetic acid, yoghurt contains lactic acid and frizzy drinks contain carbonic acid. Acids found in foods are mild. Acids such as hydrochloric acid \[(HCL),\] sulphuric acid\[({{H}_{2}}S{{O}_{4}})\] and nitric acid \[(HN{{O}_{3}})\] are called mineral acids. They are strong acids. Touching strong acids can cause acid burns. Acids are formed by dissolving oxides of non-metals such as carbon, sulphur and nitrogen in water. The oxides of non-metals are acidic because when dissolved in water they form acids For example: \[C{{O}_{2}}+{{H}_{2}}O\to {{H}_{2}}C{{O}_{3}}\] \[S{{O}_{3}}+{{H}_{2}}O\to {{H}_{2}}S{{O}_{4}}\] \[3N{{O}_{2}}+{{H}_{2}}O\to NO+2HN{{O}_{3}}\]   Behaviour of Acidic Substances The acidic substances show the following behaviour:  

• Taste sour.
• Turn blue litmus paper into red.
• Corrode metals. Acids react with metals to form a compound known as salts. For example, if iron reacts with sulphuric acid, the following reaction takes place:

\[Fe+{{H}_{2}}S{{O}_{4}}\to FeS{{O}_{4}}+{{H}_{2}}\]

• Acidic substances react with carbonates and hydrogen carbonates and liberate \[C{{O}_{2}}\] with effervescence:

\[N{{a}_{2}}C{{O}_{3}}+2HCl\to 2NaCl+{{H}_{2}}O+C{{O}_{2}}\]   Bases Bases are generally the oxides and hydroxides of metals. For example, sodium oxide \[(N{{a}_{2}}O),\] calcium oxide \[(CaO),\] sodium hydroxide \[(NaOH),\] etc. Soaps, toothpastes, solution of washing soda, soap solution, slaked lime and whitewash are some examples of basic substances. The bases that are soluble in water are called alkalis. For example, sodium hydroxide \[(NaOH),\] potassium hydroxide \[(KOH),\] calcium hydroxide \[(Ca{{(OH)}_{2}})\] and ammonium hydroxide \[(N{{H}_{4}}OH).\] Sodium hydroxide and potassium hydroxide are called caustic alkalis because they burn the skin.     Formation of Bases Bases can be formed in the following ways:    

• When the metal combines with oxygen, metallic oxide is formed.

\[2Mg+{{O}_{2}}\,\,\,\,\to \,\,\,2MgO\]

• When metals react with water or steam, metallic hydroxide is formed, which is basic in nature.

\[2Na+2{{H}_{2}}O\,\,\,\to \,\,\,\,2NaOH+{{H}_{2}}\]   Behaviour of Basic Substances The basic substances show the following behaviour:  

• Taste bitter.
• Turn red litmus into blue.
• Bases neutralise acids.
• Caustic alkalis corrode glass and some metals such as aluminium, zinc, tin and lead.

  Salts Salts are neutral substances found in abundance in the earth's crust. Salts are also dissolved in water and found in lakes, rivers and sea. Sea water contains salts such as chlorides, bromides, iodides and sulphates of sodium, potassium, magnesium and calcium. Salts are also present in fruits and vegetables.   Salts are formed in the following ways:  

• Salts are formed by the direct combination of elements:

\[2Na+C{{l}_{2\,\,}}\,\,\to \,\,\,\,\,2NaCl\,\,\]

• When acid reacts with metal:

\[Mg+2HCl\to MgC{{l}_{2}}+{{H}_{2}}\]

Weather, Climate and Adaptations of Animals to Climate   Weather Weather indicates the day to day atmospheric conditions. Atmospheric conditions include temperature, rainfall and the speed of the wind. In addition to this, weather report for a place indicates humidity levels, time of sun rise and sun set.   Temperature The maximum and minimum atmospheric temperature can be measured with the help of thermometer.   Humidity Humidity is the amount of water vapour present in the air. The capacity of the air to hold water vapour increases with temperature. The amount of water vapour present in the air expressed as a percentage of the amount of water needed for saturation at the same temperature is called relative humidity. The relative humidity is measured with an instrument called hygrometer.   Rainfall, Snow and Fog The humidity in air determines the chances of rainfall. Air when becomes saturated and Temperature of atmosphere falls, the water vapour in the air condenses. When condensation takes place high above the ground, clouds are formed. When the droplets join together and become heavy, they come down as rainfall. If raindrops pass through a very cold layer of air, they freeze and come down as hailstone. The rainfall is measured is millimetres with an instrument called rain guage. Snow is formed when the temperature in the atmosphere is very low and the droplets in a cloud freeze into crystals of ice. In winter after sunset, the water vapour near ground condenses due to low temperature. The condensed droplets in air are called fog.   Climate The average weather pattern of a place for the long time is the climate of that place. The climate of a place is determined by its latitude. The five main latitude regions of earth's surface comprise geographical zones divided by major circles of latitude. The area around the equator, which is heated by the direct rays of sun, is hot or torrid zone The area around the North Pole and the South Pole, which is cold because the rays of the sun slant the most, is called frigid zones. The region between the torrid and frigid zone is temperate zone. Rainfall is another important factor that determines the climate of a region. The degree of rainfall depends on factors such as winds, closeness to the sea and the presence of the mountains.     Adaptation of Animals to Climate Animals have to adapt to the environment in which they live to cope up with the conditions like temperature, light, moisture and availability of food.   Cold Climate Animals living in the Polar Regions such as polar bears, ermines and penguins have thick coat of fur to conserve heat. The polar animals such as polar bears and seals have very thick layer of fat under their skin. This fat layer protects these animals from cold and acts as a store of more...

Winds, Storms and Cyclones   Wind Moving air is called wind. Wind occurs due to the heating caused by the sun. The unequal heating of different parts of the earth causes the wind to blow. When the wind blows with slow speed it is called breeze. When the wind blows with high speed it is called storm.   Air Pressure Air exerts pressure. Like temperature and humidity, air pressure also determines the weather of a place on a particular day. Air pressure can be measured with an instrument called barometer.   Wind is Produced Due to Uneven Heating on the Earth by the Sun Uneven heating on the earth can take place by two situations:  

Uneven heating between the equator and the poles of the earth

Maximum heat absorbed by the regions close to the equator makes the air warm and this warm air rises creating an area of low pressure. The cooler air from the regions of upto \[30{}^\circ \] latitude belt on both the sides of the equator rushes towards the equator. Again, the air at latitudes of about \[60{}^\circ \] on both sides of the equator is warmer than at the poles. So, the cold air from the poles blows towards the warmer regions up to about \[60{}^\circ \] latitudes.    

Uneven heating of land and water of oceans

In summer land near the equator heats up faster than the water in oceans. The land air heated and rises by creating a low pressure area. This causes the wind to blow from the oceans towards the land. The winds blowing from the oceans towards the land in summer are called monsoon winds. In winters wind blows from the land towards the ocean. Rotation of earth is responsible for making the winds blow in an easterly direction instead of straight north and south direction.   Cyclones Cyclone is a type of storm that develops over sea. Cyclone has high speed wind swirling around a low pressure centre. The low pressure centre is called the eye of the cyclone. Cyclone develops mostly over tropical sea. The sunlight heated the air that creates the area of low pressure. Cold air moves into the area pushing the hot air in the upward direction. This pushing of hot air by cold air from the surrounding areas continues and thus creates a cycle or current of air. The rotation of the earth drags air current around' the low pressure area. In this way, the wind swirls around the centre. The wind swirls anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.     Cyclones that develop over western more...

Life Processes   Respiration Food provides energy to all living organisms. Food is first broken down into simple and soluble molecules. The simple molecules are then carried to all the cells. In cells, these molecules combine with oxygen to produce energy. This process of combination of simple food molecules with oxygen to produce energy is called respiration.   Types of Respiration There are two types of respirations: aerobic respiration and anaerobic respiration.  

Aerobic respiration	Anaerobic respiration
Respiration which occurs in the presence of oxygen.	Respiration which occurs in the absence of oxygen.
Production of more energy.	Production of comparatively less energy.
End products are Carbon dioxide, Water and Energy.	End products are Lactic acid, ethanol, Carbon dioxide and energy.
Example: Plants and Animals.	Ex: Some microorganisms.

  Human Respiratory System Human respiratory system consists of nose, nasal passage, trachea, bronchi, lungs and diaphragm. Our nose has two holes called nostrils. Nasal passage joins the nostrils to the trachea. Trachea is tube like structure called wind pipe. The trachea divided into two parts at The lower end called bronchi. One bronchus goes to left lung and another goes to right lung. Each bronchus divides into many smaller tubes called bronchioles. The bronchioles have air sacs called alveoli at their ends through which exchange of respiratory gases takes place between air and blood vessels. The haemoglobin present in the blood carries more...

Motion and Time   Motion If a body changes its position with time it is said to be in motion.   Different Types of Motion Motion has been broadly classified into two groups. They are uniform motion, non-uniform motion.   Uniform Motion: If a body travels equal distance in equal interval of time then it is said to be uniform motion. For example, a car travels first 30 kilometres in one hour and next 30 kilometres again in one hour and so on then we say that car has uniform motion.   Non-Uniform Motion: If a body travels unequal distance in equal interval of time then it is called non-uniform motion. For example, a car travels first 30 kilometres in one hour and next 30 kilometres in half an hour then we say that, the car has non-uniform motion.   Speed The speed of a moving body is the distance travelled per unit time. The speed of a moving body can be expressed as: \[\text{Distance}\,\,\text{=}\,\,\text{Speed}\,\,\text{ }\!\!\times\!\!\text{ }\,\,\text{Time}\] The SI unit of distance is metre (m) and of time is second (s), and the unit of speed is metre/second (m/s).   Time It important to measure time. If the time is not measured, one would not know small things such as when a train or plane will arrive. The unit of measurement of time is the time interval between two events. An event that occurs at regular interval of time is called periodic. For example, the rising of sun, changing of seasons, the waxing and waning of the moon are periodic. The rising of sun is used to measure day and cycle of seasons are used to mark a year.   Time Measuring Instruments In ancient times, instruments such as sundial, hourglass and candle clock were used for measuring time.   Sundial Sundial consists of a triangular metal plate fixed vertically at the centre of a circular plate. To measure time, sundial was placed in the sun with the triangular plate known as gnomon along the north-south direction. The position of the shadows formed by the gnomon at different times of day were used to mark the time on the circular plate or dial. Sundial told quite accurate time, but the limitation was that it could neither be used after sunset nor carried around.   Hourglass Another instrument for measuring time was hourglass. Hourglass consisted of two glass bulbs connected through small opening. One of the glass bulb was filled with sand. Sane passed from one bulb to another through small opening. When all the sand from one bulb had passed to another, the instrument can be inverted to measure the time again   Candle Clock Another instrument for measuring time was candle clock. The candle was marked with numbers. As the candle burnt, the marking indicated time.   Pendulum Clock The modern time measuring instrument is pendulum clock. An Italian astronomer Galileo Galilei discovered that the motion of a pendulum is periodic and can more...

Electricity and Light   Electricity All electrical devices such as torches, fans, washing machines, music systems, etc. work on electricity. These devices work when electric current flows through them. The flow of electricity is called current. Current flows through an electric device when voltage is supplied across the device. The amount of current that flows depends on the amount of voltage supplied. The unit of measurement of voltage is volts (V). Voltage is supplied through electric cells and main electric supply.   Electric Circuit An electric circuit is a path through which electric current flows. An electric circuit includes a source of electricity, conductors and a device that uses electricity. The source of electricity can be a cell, the conductor can be a wire and a device that uses electricity can be an electric bulb.   The electric circuit can be diagrammatically represented with the help of a circuit diagram. A circuit diagram represents circuit using symbols for its components.                                     Resistance The electrical resistance of a material is the measure of hindrance, the material creates in the flow of electric current through it. The high the resistance of a material, less the amount of current flows through it. In addition to material, the resistance also depends on the thickness and length of the material used. A thin wire has a higher resistance than a thick wire. Similarly a long wire has a higher resistance than a short wire. Material such as metals have low electrical resistance. These materials allow electricity to flow through them and are called good conductors or simply conductors. Material such as wood, rubber and plastic have high electrical resistance. These materials do not conduct electricity. These are called bad conductors or insulators.   Heating Effect of Current Heat is produced when current flows through a conductor. The heat produced depends upon the following factors:  

• The higher the electrical resistance of a material, the greater is the heat produced
• For a given electrical resistance, the greater the current, the greater is the heat produced.

  Disadvantages of Heat Production When current passes through a conductor, heat is produced due to the conversion of some amount of electrical energy to heat energy. This conversion of electrical energy to heat energy is a waste of energy. The heat produced can cause damage to electrical components or can cause fires. Fuse is an electrical device used as a safety measure that opens an electric circuit when excessive current flows through it.   Uses of Heating Effect Electric bulbs work on the heating effect of electrical current. The bulb has a more...

Our Environment   Soil Soil is the uppermost layer of the earth's crust. Soil is formed by the weathering of rocks. The weathering of rocks takes place as a result of natural factors such as temperature change, rain and wind. Soil supports growth of plants.   Layers of Soil Soil consists of layers. Layers of soil are called horizons. The various layers of soil are:     A-horizon: This is the uppermost layer of the soil. This layer is also called topsoil. It is dark in colour due to the presence of humus.   B-horizon: This layer is below the topsoil and is called subsoil. This soil is lighter in colour. The particles of this layer are coarser and porous. This layer does not contain much humus and thus not suitable for plants growth.   C-horizon: This layer is below subsoil and is called substratum. This layer is derived from hard rocks that lie beneath it.   R-horizon: This layer is below the substratum. It consists of hard rock called bedrock. Water cannot penetrate the bedrock and thus accumulates in the substratum.   Components of Soil Main components of soil are different sized rock particles and humus. On the basis of their sizes, rock particles have been classified into four groups.   Clay: Clays are the smallest rock particles present in the soil. They are smooth to touch.   Silt: Silts are the rock particles which are a little larger than clay particles. Silt particle are not as smooth as clay particles.             Sand: Rock particles which are larger than silt particles form sand. Sand particles have rough texture.   Gravel: The largest rock particles present in the soil form gravel.   Types of Soil   Sandy Soil: It consists of mainly sand. A little amount of silt and clay are also present in it.   Clayey Soil: It consists of mainly clay particles. Clay particles are very fine so it has very good water holding capacity.   Loamy Soil: Loamy soil consists of clay, silt and sand in right proportion. It also contain sufficient amount of humus. Therefore, loamy soil is the most fertile soil.   Forests: Our Lifeline Forests are important for maintaining environmental balance and controlling pollution.   Functions of Forests  

• Maintains balance of gases: Forests maintain the balance of carbon dioxide and oxygen by using carbon dioxide and releasing oxygen.
• Checks pollution: Forests absorb dust and other pollutants. Forests absorb noise and act as barrier against wind.
• Protects soil: The roots of trees bind soil and prevent it from being washed away by rain water or blown by wind. The leaves of tree protect soil from direct rain showers. The leaves that fall get decomposed and make the soil fertile.
• Controls floods and droughts: Forests prevent water from more...

Reasoning and Aptitude   Learning process is dependent on ones ability to think logically and reason quickly and effectively. So Reasoning and logic skills are an important part in our progress as these skills are very useful m our day to day life. In this chapter, we will learn various problems related to reasoning and aptitude.   Problems Based on Inserting a Latter In these types of problems, you are given two sets of two different words. The last letter of the first word and the first letter of the second word in each problems are left blank. You have to fill that letter which completes both the words.   Ø  Example: (a) E                            (b) K (c) T                             (d) L (e) None of these   Answer (b) Explanation: Clearly the letter T will completed all four words. RISK, KIND, SICK, KITE    Problems Based on Logical Operators In these types of problems, we have to read the statements and on the basis of these statements, we have to find out the correct conclusions out of the given conclusions.   Ø  Example: Statements: Conclusions: I.                         II.   III. (a) only I is true (b) only II is true (c) only III is true (d) Both II and III are true (e) None of these   Answer (d) Explanation:and              and   Problems Based on Cube On folding a sheet to form a cubical box, we may get following forms:   Case I: more...

  Notice, Message and Report   Notice Importance of Books   1.            You are head student of your School. Write a notice for school Notice Board informing all the students for a picnic party organised by the school, Sign yourself as Gita /Gagan.                   2.            You are Harish/ Hanshika, Secretary of school cultural club. Write a notice; for school Notice Board that school is going to celebrate Holi festival, Celebrating Holi festival.                   3.            You are Indu /Imtihan, a yoga teacher of your school. Baba Ramdev is coming to show some yoga to your school students. Write a notice for school notice board inviting the students to be a part of the yoga session.         4.            You are Jagjit / Jassy, examination in-charge of your school. Write a notice for school notice board and tell the date-sheet of exam for all the classes. Exam Date Sheet         5.            You are Kavita /Kaveer, Secretary of Extra Curriculum activities. Write a notice to the students informing about a debate competition between your school and G.S.S. School, Rani Bagh.                   1.            Read the following between Miss. Diya Mrs. Suman.             Miss Diya: May I talk to Divya please?             Mrs. Suman: I am sorry, but Divya is not at home, this moment May I know who I am speaking to?             Miss Diya: I am Diva her classmate. When she will be back?             Mrs. Suman: She will be back by 6.00 p.m. She has gone for her music class,             Miss Diya: Can you inform her that tomorrow school is closed'?'             Mrs. Suman: Sure, I'll do more...

  Letters   Study the following examples.   ·                     Example 1               Two months ago you bought a Titan Watch which has 2 years warranty but it is not working properly. Write a letter to the Assistant Manager, Sales and Service Department, Bahadur Shah Zafar Marg, New Delhi-110004, asking for a replacement. Sign yourself as Deepika / Deepak.               D-410, Ram Bagh,             New Delhi-110034             July 10, 2008             The Assistant Manager             Sales and Service Department             Bahadur Shah Jafar Marg,             New Delhi-110004             Sir/Madam,               Subject: Replacement of Titan Wrist Watch               I am Deepak, a customer of Titan Watch. I bought a wrist watch in May from a dealer in Rani Bagh. It is still under warranty. But from the last few days it is not working properly. I went to shopkeeper, then he advised me to contact the company directly for the services.             I hereby request to you to do the needful and replace it. I will be obliged if you attend the matter as soon as possible.             Yours faithfully,             Deepak   ·                     Example 2               You are Leela / Lalit, write a letter to your father for demanding some money. You didn't receive any money for the last three months.               Dear Daddy,             I am happy to know that you are fine there. I have been awarded three medals for the sports competition, which was held in the last month. I didn't receive any money from you for my day to day expenses. I understand how difficult it is for you to maintain the family Hope you understand the problem. It is also difficult for me to stay in a city like Delhi without money. Otherwise, I have to do some work to maintain my expenses.             Kindly send me some money. Best washes to Chintu and love you dad and mummy.               Yours lovingly,             Lalit   ·                     Example 3

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