Current Affairs 7th Class

       High Speed Winds   Wind is the motion of air. Motion of air is due to the uneven heating of the Earth by solar radiation. The part of the Earth receiving less amount of solar energy are less heated as compare to those part which receive greater amount of solar radiation. Air travels from high pressure area to lower pressure area causing the movement of air. Therefore, the movement of air depends on the amount of heat received by an area from the solar radiation.   Look at the following picture of flow of air from high to low pressure area   Polar region receives less Sun rays in comparison to equator and from the other parts of the earth. Hence the climate of the polar region is cold. The area at equator receives maximum sunlight, thereby making the climate warm and hot. The speed of the wind depends on the heating of atmosphere by the solar radiation. More heat causes the high speed of movement of wind whereas less heat causes the low speed of movement of wind. The equator of the earth is at 0° latitude. South Pole of the earth is at 90°(S) latitude, and North Pole is at 90° (N) latitude.   Look at the following picture of flow of wind     Wind blows north to south is known as north wind, as it originates in north. West wind blows towards east direction and vice versa. Low pressure area on the Earth causes the high speed of wind, which is formed due to temperature changes as well as revolution of the Earth. The speed of the wind is affected by mountains, earth crust and plants.

       Atmospheric Pressure   Atmospheric pressure is the air pressure on the Earth. Pressure at an unit area of the Earth is measured by the total weight of air above that unit area. The weight of air above the unit area of the Earth depends on the presence of water, gas and dust particles. Air pressure is varied according to the location and time, as the amount of air is varied from time to time. Density of air decreases on increasing height, therefore it causes the decreasing of air pressure. Due to the absence of life supporting elements, i.e., absence of required oxygen, low air pressure in outer space etc, an astronaut requires oxygen while going in space. The dress, which supports the appropriate atmospheric pressure is provided to the astronauts. Special designed dresses protect them from low air pressure.               Which one of the following devices is used for the measurement of air pressure? (a) Barometer (b) Thermometer (c) Potentiometer (d) All of these (e) None of these   Answer: (a)            Air pressure on the Mount Everest with respect to sea level is? (a) Greater (b) Smaller (c) Equal (d) All of these (e) None of these   Answer: (b)

     Atmosphere   Atmosphere of the Earth is best described by the temperature and presence of percentage of gases in air. Atmosphere protects living organisms form harmful ultraviolet radiation from the Sun. Temperature on the surface of the Earth is also influenced by atmosphere. Atmosphere of the earth is layered, which is divided into five main layers according to the height or altitude, and on increasing and decreasing temperature. The layers of atmosphere of the earth are, troposphere, stratosphere, mesosphere, thermosphere and exosphere. The first layer from the surface of the earth is troposphere. Troposphere is heated by the reflected sun rays of  the earth surface. It is spread about 8 km above the surface from pole and 18km above form the equator. The interface between troposphere and stratosphere is called Tropopause. The layer above the tropopause is stratosphere. It is about 50 km from the tropopause. Ozone layer is within the layer of stratosphere. The thickness of the ozone layer is about 15 to 35 km, which varies according to the season. Atmospheric pressure in the stratosphere layer is negligible. Temperature is increased as the altitude is increased. Stratopause is the boundary between stratosphere and mesosphere. Mesosphere is extended up to 88 km from stratopause. In this layer most meteors burn up when they enter in the layer. In this layer, as the altitude increases, temperature decreases. Water vapor in this region is frozen into ice due to the extreme cold. The layer above the mesopause is thermosphere. Temperature of the thermosphere is varied according to the solar activity. The region of the thermosphere is between 100 to 800 km. The layer above the thermosphere is exosphere. A layer, which is known as ionosphere is between the thermosphere and exosphere. The ionosphere is ionized by solar radiation. Radio propagation on the Earth is due to the magnetosphere of ionosphere. Exosphere is the outer most layer of atmosphere of the Earth. The exosphere is mainly consisting of hydrogen and helium gases. Density of the gases in this layer is very thin and particles are apart from each others. In this region solar wind is continuously flowing. Exosphere is extended up to about 10000 km.   Look at the following picture of layers of Earth's atmosphere                     The earth's atmosphere is layered according to the availability of gases, temperature and altitude. Which one of the following layers is found between the thermosphere and stratosphere? (a) Troposphere (b) Exosphere (c) Mesosphere (d) All of these (e) None of these   Answer: (c)           Tropopause is the boundary in the Earth atmosphere lies between in which one of the following layers? (a) Between the thermosphere and exosphere (b) Between the troposphere and stratosphere (c) Between the stratosphere and mesosphere (d) more...

         Air Around us   Every empty space is filled with air. Air is a mixture of gases. It contains 78% of nitrogen, 21% of oxygen, and small amount of other gases. Air also contains water vapor, which comes from the evaporation of water. Atmosphere of the Earth is extended up to several kilometers above the surface. The percent of gases and dirt particle in air, including water vapor, vary slightly according to the altitude and location. For example, air contains small amount of water vapor in desert as well as in low temperate zone. The pressure exerted by atmosphere on Earth is called the atmospheric pressure. Atmospheric pressure is caused by the weight of air in atmosphere. A pressure measuring device/called barometer is used for the measurement of atmospheric pressure. An air filled car tier is heavier than an empty tier, it proves that air has weight. A balloon inflates when air fills inside of it, therefore, air exerts pressure.             Fig. (1)                                                        Fig. (2)   In figure (1), water filled bottle is punched. The cap of bottle is screwed tightly. Empty part of bottle is filled with air and extra air cannot enter through the cap as it is airtight. Thus water drops stop flowing from the holes. Flow of drops of water stops as the water inside the bottle does not get extra pressure from outer air. In figure (2), big hole causes the heavy flow of water from the bottle. Air continues. to pass through the big holes due to outer air pressure.     Fig. (1) A deflated balloon                            Fig. (2) An inflated balloon   Air expands when heat is applied, which is clear by the above pictures. A water containing bottle gets heated and a balloon on the mouth of the bottle is inflated. From the above experiment, it is clear that when heat is applied on a water containing jar, the upper part of jar that contains air gets heated and expands causing the balloon to inflate by hot air. A heater below the bottle gives heat to the steel pot. Upper part of both the bottle is empty. Air blows from high pressure area to low pressure. Warm air moves up. Cold air fills the gap made by the movement of hot air upwards. The pressure of air can be observed while riding a bicycle. When air blows from north to south and a bicycle rider riding the bicycle towards south gets extra support from air and while riding the bicycle in opposite direction, air pushes the bicycle rider in opposite direction.   Look at the following pictures                                  In the picture (1), two paper boxes of equal weight more...

         Fuses   Fuse is a safety device used to protect electric circuit and other electrical devices like, bulbs, tube lights, fans, TV, refrigerators etc. from being damaged of excessive current flow. Sometimes, due to touching of live wire with neutral wire, known as short circuit, excessive amount of current passes through the wire. This excessive amount of current causes production of large amount of heat. As a result the wire gets burnt and the house may catch fire. Overloading is another major danger which sometimes causes fire and other damages. Thus to protect our houses and other electrical appliances from these problems, fuses are used.                 A fuse consists of a strip of low melting alloy. In case of over loading or short circuiting, the alloy wire of the fuse gets melted immediately. As a result, the circuit of electricity breaks and supplying is stopped. In this way other electrical appliances are saved from damage.                 The wire of greater resistance produces greater amount of heat energy' is the above statement true ? (a) Yes                                                                  (b) No (c) Resistance has nothing to do with heat (d) All of these (e) None of these   Answers (a)            Which one of the following is an insulator? (a) Water (b) Human body (c) Dried wood (d) Iron nail (e) None of these   Answer: (c)     Flow of electrons through a wire is called electricity. The path, in which electrons move to produce electricity, is called electric circuit. A simple electric circuit is composed of a battery, wire and a switch. Fuse is a safety device which protects the electric appliances in case of short circuiting and overloading. When current is passed from a wire the heat energy is produced, the phenomenon is known as heating effect of current. Bulb is an instrument, which works on the heating effect of current. When current moves from a conductor wire, it acts as a bar magnet. This phenomenon is known as magnetic effect of current. Electric bell works on magnetic effect of current.

       Electromagnet   Electromagnet is a magnet prepared by using the effect of magnetism of electric current. It consists of long, coiled copper wire wrapped around a iron rod. When current is passed through the wire, it behaves like a magnet, called electromagnet.               Applications of Electromagnet Electromagnet has a number of applications as the magnetism of electromagnet can be switched on or switched off as per our wishes. Its strength can be increased or decreased as per our requirements. It is used in a number of devices like electric bell, fans, toys etc..

       Effects Due to Movement of Electric Charges   Moving charged particles produce some special kinds of effect, i.e. heating effect, magnetic effect, chemical effect, etc. These effects are made useful by various electrical instruments, like, bulb, heater, fan, etc. Thus electric energy is utilized by using the effects produced by the charge particles when they move.               Heating Effect Charged particles have to do work to move through a substance. Substances are made up of atoms. So when charged particles move through them, they collide with the atoms of the substance. This collision changes a part of mechanical energy of electron into heat energy. Therefore, when electric charges flow through a substance, the substance gets heated. This phenomenon is known as heating effect of electricity. In other words, heating effect is the phenomenon in which electric energy changes into heat energy.     The amount of heat produced in the wire depends on the two factors:               Amount of Current Passes through the Wire As the amount of current passing through the wire increases, amount of heat produced in the wire also increases. And, as the amount of current passing through the wire decreases, amount of heat produced in the wire also decreases. We can therefore conclude that the amount of heat produced in the wire is directly proportional to the amount of current passing through the wire.               The Resistance that the Wire Offer to the moving Charged Particles The resistance of a wire depends on its nature. If the wire offers greater resistance, the higher amount of heat is produced. And if the wire offers less resistance, less amount of heat is produced. Thus, amount of heat produced in the wire is directly proportional to the resistance of the wire.               Applications of Heating Effects of Current There a number of electrical instruments like bulb, heater, iron etc have been prepared to utilize this heat energy produced in the wire. Bulb is used for producing light.                Magnetic Effect In 1820, Hans Christian Oersted noticed a deflection of magnetic needle, placed near to the current carrying wire. He found that it was because of appearance of a force produced by current carrying conductor. Like a magnet, a current carrying conductor also applies a force on magnets when they are brought close. Thus when current passes through a wire, it acts as a magnet and produce a magnetic field. This phenomenon is called the magnetic effect of current.                Applications of Magnetic Effects of more...

         Electric Circuit   We know that when charged particles move, electricity is produced. For continue production of electricity, charge particles required to move continuously. Therefore, a path is prepared through which charge particles (electrons or charged atoms) keep on circulating. Thus electricity is produced continuously. The path through which charge particles move is called electric circuit.     A simple electric circuit is composed of a battery, wire, and a switch. One end of the wire is connected to the negative terminal of the battery and the other end of the wire is connected to the positive terminal of the battery. Switch is fitted in the wire in such a way that when switch is on, the wires of the circuit are connected and current is passed. When the switch is off, the wires are disconnected and the current cannotpassed through the circuit. Thus the switch gives us the facility of using electrical energy as per our requirement. Different electrical appliances are fitted in the circuit for different purposes.       Switch                      Cell                    Battery         Lamp              Voltmeter             Ammeter      Register             Deregister            Motor                Resistance Resistance is the force that oppose the flow of electrons in a conductor. Resistance of a matter depends on its nature. Generally metals offer lower resistance, whereas non-metals offer higher resistance. Moreover, the resistance of a wire also depends on the thickness and length of the wire.              Resistance Due to Thickness If the thickness of the wire is increased, it will offer less resistance and if the thickness of the wire is decreased, it will offer greater resistance.                  Low resistance                        High resistance                 Resistance Due to Length If the length of the wire is increased, it will offer higher resistance and if the length of the wire is decreased, it will offer less resistance.             High resistance                          Low resistance                   Conductor and Insulator For the production of electricity a path is needed through which charge particles keep on moving. The substances, which allow the charge particles to move through themselves, are called conductors. In other words, conductors are the substances, which give the way for movement of charge particles through themselves. For example, silver, copper, aluminum, gold etc. are conductors. Insulators more...

         Charged Particles   Electron, Proton and Neutron are the three fundamental particles, which an atom is made up of. Out of the three, electron and proton are charged particles, whereas neutron is the neutral particle. Electron is negatively charged and proton is positively charged. Magnitude of charge on a proton is equal to that of an electron, but nature of the charge is opposite.     In an atom, number of protons is equal to the number of electrons. Therefore, atoms are neutral. But transfer of electrons from one atom to other atom causes the atoms to be charged. The atom, which looses the electrons gets positively charged because number of positively charged particle (protons) in the atom gets greater than that of negatively charged particles (electrons). Therefore, magnitude of total positive charge becomes greater than that of negative charge. And the atom, which receives the electrons gets negatively charged, because number of negatively charged particle (electrons) in the atom gets greater than that of positively charged particles (protons). Hence, total magnitude of positive charge becomes greater than that of negative charge.              Charge Produced Due to Direction Proton and neutron are present in the center of an atom, which is called nucleus. The electrons are revolving around the nucleus. The electrons close to the nucleus are tightly held by force of attraction produced by protons. And the electrons, which are far from the nucleus are loosely held; because force of attraction becomes weaker as the distance increases. When we rub two substances with each other, some electrons, which are loosely held by nucleus, are transferred from one substance to other. As a result, the is substance that looses electrons, gets positively charged and the substance that gains electrons, gets negatively charged.                  Force Around a Charged Particles Charged particles have a force around them. This force can be experienced by bringing another charged particle close to them. Nature of the force is attraction or repulsion depending on the nature of the charged particles. If the charged particles are alike (both positively charged or both negatively charged), the force of repulsion works between them. And if charged particles are unlike (one positively charged and other negatively charged), the force of attraction works between them. This is why between two protons or two electrons there is a force of repulsion and between an electron and a proton there is a force of attraction.              Movement of charged particles Moving of charged particles has a number of applications for us, as this movement produces electricity. We already know that protons and electrons are the charged particles and when transfer of electrons occurs between two atoms, more...

      Electricity   It has been observed that when charged particles move, a special kind of effect is produced which can be used for various applications, as it posses energy. This form of energy is called electrical energy, electric current or electricity. In other words, electricity is a form of energy, which is produced when charged particles move. Electricity can also be defined as flow of electrons through a conductor wire. It is convenient to utilize electric energy .Therefore different sources of energy (fossil fuel, water, wind, etc.) is harvested to generate electrical energy, which is then converted into different other forms of energy ,i.e. heat energy, light energy, sound energy etc., as per our requirement.                 Production of Electricity Electricity is produced by harvesting various resources like fossil fuel, wind, water, solar energy etc. and is directly supplied to our houses. Various instruments for generating electricity has been developed, for example, cell, battery, generator etc., as per our requirements.