Wednesday, December 12, 2018

science pg 26-35 van 2

ELECTRIC CURRENT AND ITS EFFECTS
Symbols of electric components
 Not much important
Battery – combination of two or more cells.
 The batteries which we see in vehicles is called as automotive battery.

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Automotive battery
 An automotive battery is a rechargeable battery that supplies electric energy to an automobile.
 These batteries are lead-acid type and provide 12.6 volts of direct current.
 The battery is actually six cells connected in series.
 Battery electric vehicles are powered by a high-voltage electric vehicle battery, but they usually have an automotive battery as well, so that it can be equipped with standard automotive accessories which are designed to run on 12 V.
Electric circuit
 An electric circuit is like a pathway made of wires that electrons can flow through.
 A battery or other power source gives the force (voltage) that makes the electrons move. When the electrons get to a device like a light bulb, your computer, or a refrigerator, they give it the power to make it work.
Heating effect of electric current

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 If wire used in electric circuit has higher resistance, then it gets hot and this is the heating effect of the electric current.
 An electric room heater or an electric heater contain a coil of wire. This coil of wire is called an element.
 Electrical appliances such as immersion heaters, hotplates, irons, geysers, electric kettles, hair dryers, have elements inside them.
 The amount of heat produced in a wire depends on its –
o Material

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o Length
o Thickness
 This is the reason that electric iron or immersion rod has thicker wire.
 The wires used in electric circuit don’t heat easily while filament wire of bulb heats so fast that it is easily available.
 An electric bulb is used for light but it also gives heat.
 This heat is not desirable + wastage of electricity.
 Use fluorescent tube lights or Compact fluorescent lamps (CFLs) in place of bulb to reduce wastage.
 Now days LED (light emitting diodes) are used which are even more efficient than CFL and fluorescent lamps.
 Before buying bulbs or tubes, or CFLs, one should look for the ISI mark (ensures that the appliance is safe and wastage of energy is minimum) of the Bureau of Indian Standards
Led
 An LED lamp is a light-emitting diode (LED) product which is assembled into a lamp (or light bulb) for use in lighting fixtures.
 Lifespan and electrical efficiency several times greater than incandescent lamps.
Bureau of Indian Standards
 BIS is the National Standard Body of India established under the BIS Act 1986 for the harmonious development of the activities of standardization, marking and quality certification of goods and for matters connected therewith or incidental thereof.
 Keeping in view, the interest of consumers as well as the industry, BIS is involved in various activities as given below:
o Standards Formulation
o Product Certification Scheme
o Compulsory Registration Scheme
o Foreign Manufacturers Certification Scheme

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o Hall Marking Scheme
o Laboratory Services
o Laboratory Recognition Scheme
o Sale of Indian Standards
o Consumer Affairs Activities
o Promotional Activities
o Training Services, National & International level
o Information Services
Electric fuses
 Sometimes large current passes through wire and this can raise the temperature of wire so much that it can melt and break. Such wires are made of special metals and are used for electric fuses.
 There would be a limit on maximum current which can flow from a circuit. If current exceeded from this limit then it may cause fire in circuit or make appliances dysfunctional.
 So, electric fuses are used to avoid such situations. In case of high current flow, the wire will melt and circuit will be protected.
 In the below image you have seen such fuses used in your houses.
Reasons for excessive current flow –
 Short circuiting of wire (touching of live and neutral wire)
 Connection of many devices to a single socket.

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MCB (Miniature circuit breakers)
 Now days MCBs are used in place of electric fuses.
 These are like electrical switches which turn off automatically when excessive current flows in circuit.
 We can turn it on when we feel that now circuit has no short-circuit.
 By just turning it on the circuit gets completed.
Advantages of MCB than fuse –
1. It automatically switches off circuit during over load condition or faulty condition. MCB is much more sensitive to over current than fuse.
2. As the switch of MCB comes to off position during tripping, the faulty zone of the electrical circuit can easily be identified. But in case of fuse, fuse wire should be checked by opening fuse grip or cutout from fuse base, for confirming the blow of fuse wire.

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3. Quick restoration of supply not possible in case of fuse because faulty wire has to be replaced with new wire. But in the case of MCB we have to just switch on the MCB for supply restoration.
4. Handling MCB is more electrically safe than fuse.
Disadvantage of MCB
1. Costlier than fuse.
Magnetic effect of electric current
 A scientist called Hans Christian Oersted discovered that the needle of a compass, which is kept near an electric wire, deflects every time the current was passed through the wire.
 It is because the wire through which current passes behaves like a magnet.
Electromagnet
 An electric current can be used to make magnets.
 If a wire is coiled around an object and if current is passed through that coiled wire, then it will act as electromagnet. The coiled wire acts as temporary magnet.
 It has magnetic properties till current is passing through it. As soon as the current stops it’s just a coil.
 Uses of electromagnet
o All kinds of electric devices, including hard disk drives, speakers, motors, and generators, as well as in scrap yards to pick up heavy scrap metal.
o Also used in MRI machines, which utilize magnets to take photos of your insides!
o Doctors use tiny electromagnets to take out small pieces of magnetic material that have accidentally fallen in the eye.
o Many toys also used electromagnets.
Electric bell
 Electric bells also used electromagnets.

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 As you can see in image it has a gong, a hammer and a coil.
 When the switch is pressed the electric current flows through the coil it acts as electromagnet.
 Because the hammer is attached with coil, hammer also acts as electromagnet.
 As soon as the hammer becomes electromagnet it attracts the gong and a sound is produced. (the gong cannot move and so the hammer attracted towards the gong and strikes the gong)
 As the switch is released the hammer not remains electromagnet ? no attraction ? sound is stopped.

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WASTE WATER STORY
 Wastewater – water mixed with pollutants and contaminants like lather, oil, water that goes down the drains from sinks, showers, toilets, laundries etc. is waste water.
 We should not waste it instead it should be used for other purposes but only after cleaning.
Water, our lifeline
 We know the importance of the clean water in our life.
 But unfortunately it is not available to everyone.
 About one billion people don’t have access to clean water and so there are large no. of water borne diseases.
 An international day to celebrate freshwater was recommended at the 1992 United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro. The United Nations General Assembly responded by designating 22 March 1993 as the first World Water Day.
 In 2005 UNGA proclaimed the period 2005 – 2015 as the International Decade for action on “Water for life”.
 All efforts made during this decade aim to reduce by half the number of people who do not have access to safe drinking water.
 2016 Theme: Better Water, Better Jobs
 Cleaning of water - A process of removing pollutants before it enters a water body or is reused. This process of wastewater treatment is commonly known as “Sewage Treatment”.
 Cleaning of water takes place in several stages.
What is sewage?
 Sewage – wastewater released by homes, industries, hospitals, offices and other users.
o It also includes rainwater that has run down the street during a storm or heavy rain mixed with soil, concretes waste etc.
o It is a liquid waste
o The impurities inside sewage are called as contaminants.
 sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes.
o Organic impurities – Human faeces, animal waste, oil, urea (urine), pesticides, herbicides, fruit and vegetable waste, etc.
o Inorganic impurities – Nitrates, Phosphates, metals.
o Nutrients – Phosphorus and Nitrogen.
o Bacteria – Such as which cause cholera and typhoid.
o Other microbes – Such as which cause dysentery.
Waste water treatment plant (WWTP)

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Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates the wastewater.
1. Bar screen – it clears large objects like rags, sticks, cans, plastic packets, napkins etc.

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2. Grit tank - speed of the incoming wastewater is decreased to allow sand, grit and pebbles to settle down.
3. Settling tank - water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. Skimmer removes the floatable solids like oil and grease. At this stage water is known as clarified water.
a. Now water is transferred to another tank where anaerobic bacteria decomposes the waste in water. While decomposing they may produce biogas which can be used to produce electricity.
4. Aeration tank - Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water.
After several hours the microbes settled in the bottom of tank as activated sludge (about 97%). Now water can be removed from above. The dried sludge can be used as manure, returning nutrients and organic matter to soil.
Treated water consists low amount of organic material and so now it can be safely discharged into sea, river or ground. Nature has its own ways to clean the water and so it will be further cleaned.
But sometimes it is necessary to disinfect water with chemicals like chlorine or ozone before releasing it into distribution system.
 In the battle of wastewater treatment eucalyptus can prove effective as they absorbs surplus wastewater rapidly and release pure water vapor into the atmosphere.
Sanitation and disease
 Poor sanitation and contaminated drinking water is the cause of a large number of diseases.
 That’s why our PM had started the Swachh bharat mission.
 Open defecation is one of the major problem as untreated human excreta is a health hazard. It causes water pollution and soil pollution.
 When we say water pollution, here it means surface water as well as ground water. Pollution of water can result in water borne diseases like cholera, typhoid, polio, meningitis and hepatitis and dysentery.


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