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 more...

       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.     more...

     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 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, 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 more...

       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 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 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 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 more...