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8/14/2019 Energy(educationpoint.co.cc)

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LECTURE NOTES PHYSICS STEPS A TCY Program _______________________________________________________________________________________

STEPS ____________________________________________________________ G e t f r e e c h a p t e r w i s e t e s t s f o r C l a s s X t h o n

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SOURCES OF ENERGY

Importance of Energy: Energy is required for (a) Cooking Food (b) Lighting (c) Transport(d) Running machines and gadgets (e) entertainment (f) Agriculture (g) Producing goods in

factory etc. In fact it is difficult to imagine life without energy.

Sun The Ultimate Source of Energy:

Earth receives energy from the Sun in the form of (a) heat (b) light This is the ultimate source of energy and all other forms of energy available results fromSolar Energy.

Useful Energy or net Energy: When we derive energy from a source it is often necessarythat we need to provide an amount of input energy. For example to burn a matchstick wehave to do work on it by rubbing it against a rough surface. When the input energy isgiven the fuel source give certain amount of output energy. For any fuel source; InputEnergy < Output Energy

The difference in input and output energies is called useful energy .

Essential characteristics of a good source of energy:(a) It should be capable of providing adequate amount of useful energy.(b) The source should be capable of giving out energy in a Steady rate.(c) It should be safe and convenient to use.(d) It should be easy to store and transport.

We generally use energy as fuel or electricity to meet our requirements. Technology helps us in converting other sources of energy into these forms.

NonRenewable Energy Sources: Some energy sources like coal and petroleum wereformed over millions of years under special conditions. Since these conditions are notprevalent now they are called rare or nonrenewable Sources. By year 2020 it is estimatedthat India and would exhaust is known oil reserves and in another 250 years its coalreserves.

The use of nonrenewable sources of energy should be discouraged because:

(a) They would deplete since replacement is not taking place.(b) They are a major case of environment pollution.

The depletion of coal supply is accelerated by(i) Depletion of petroleum oil(ii) Growing populations(iii) Increasing rate of consumption of energy


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Renewable Sources of Energy: The sources of energy that are likely to be available for along time and in abundance is called Renewable sources of energy.

The importance of classification of fuel sources: The classification of fuels into renewable and nonrenewable is extremely useful.(a) It helps us in identifying fuel sources that are to be conserved.(b) The knowledge that certain sources would be depleted encourages us to look for

alternate sources of energy which increases the technological development.

SOLAR ENERGY NATURE AND COMPOSITION

The sun gets its energy from nuclear fusion reactions. The Earth receives a tiny fraction of this energy. The radiation from Sun consists of (a) Heat radiation (Infra Red)(b) Visible light(c) Ultra violet radiations

(d) Gamma rays

Solar Constant: The energy from sun felling on 1m 2 Area in 1 second on the periphery of the earths atmosphere is called Solar Constant (1400 J/m 2 /see.)It is estimated on the basis of solar radiation received on unit area perpendicular to thedirection of the ray at as average distance between sun and earth.

Energy received at the surface of the earth:

1400 J of energy reaches a 1m 2 area on the periphery of earths atmosphere but 53% of the energy is reflected or absorbed and only 47% of this energy reaches the earth surface.

Atmosphere absorbs the harmful U V radiations. The energy reaching earth is alsoabsorbed by land mass and water bodies inducing many biological and physical changeslike, photosynthesis, wind, storms, ocean waves, rain and snow fall.

Earth

periphery of earths atmosphere

Sun

1400 J/m 2 /s

47%

53% absorbed& reflected


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The Infrared radiations Properties:(a) Heat from sun is transferred in the form of Infra Red radiations.(b) All hot bodies emit InfraRed radiations.(c) One third of the sunrays are compared of Infra Red radiation.(d) It heats up any body that comes in its path.(e) A hotter body could emit infrared rays of shorter wavelength than a colder body.

Uses of Solar Energy: The ancient uses.(a) Drying of food grains, fish and firewood.(b) Drying of clothes.(c) Obtaining salt from sea water etc.

The modern uses:(a) In cooking with the help of Solar Cookers.(b) Generating electricity in Solar Cells.

(c) In water heating and space heating.(d) Agricultural uses like water pump and green houses.

Two principles on which Solar Devices works: The energy incident on Earths surface is around 660J/sec. This is a very minute amount of energy. So any solar device function by(a) Collecting and focusing heat from a large area into a smaller area.

(e.g. solar cookers, geysers etc.)(b) Converting Solar Energy into Electrical Energy.

(e.g. water pump etc.)

Solar Cooker: The most important parts of a Solar Cooker are(a) Reflector(b) Glass Sheet(c) Insulated box

Reflectors: The function of the reflector is to increase the amount of energy incident onthe glass pane of the Solar Cooker. It collects energy incident from a large area and focuson the Glass pane. For higher temperature a parabolic or spherical mirror is used.

Glass sheet: Glass sheet has the property of allowing infrared radiations of smaller wavelength to pass through but block infrared radiations of larger wavelengths frompassing out of the cooker. Since the radiations coming in are of smaller wavelength and

Glasssheet

Reflector


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the radiation emitted by the inside the cooker is of larger wavelength, heat builds upgradually in the cooker to reach temperatures of 100 140 oC.

Insulating box: The box in which the Solar cooker in encased is insulated to preventleakage of heat into the environment.

Black coating: The inner walls and the cooking containers are painted black since blackis a good absorber as well as emitter of heat radiations.

Miscellaneous: Solar Cookers can be used to prepare slow cooking items only. Howevertwo to three items can be cooked simultaneously in this cooker.

GREEN HOUSE EFFECT AND A CAR PLACED IN SUN

A green house: It is a glass structure used to protect plants from cold conditions.

Green house effect: Some enclosed structures allow heat radiations of shorter wavelength to come in but does not allow layer wavelength to go out resulting in heatingup of interiors.

Since the wavelength of radiations emitted by a hotter body is smaller. The radiationsemitted by sun has very small wavelength so it can enter inside a car parked in the sunthrough the glass but the heat radiation emitted by the interiors of car are longer due tothe low temperature hence it cannot escape out through the glass. This results in buildingup of heat inside the car. This process is called green house effect.

Solar Water Heater: In solar water heaters a copper pipe painted black is coiled as shownin figure. The coiling of the pipe increases the surface area exposed to heat radiations. Thecopper pipe is placed in an insulated box with a glass pane.

Hot water

Glass pane

Cold water

Cold Water Tank

Hot water to tap

Cold water flowTo tap

Hot water

Hot water

(1)(4)

(2)

(3)

Solar Energy


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Solar Concentrators: A solar concentrator is a device usually a parabolic or sphericalconverging mirror used to focus energy from a large area into a small area. Someadvanced concentrators can move so that it always faces the sun. a simple concentratorcan achieve high temperatures upto 180-200 oC the solar cookers of this type can be usedfor frying and baking too

Solar Power Tower: Solar power tower refers to an array of concentrators focusing energyon a small area and generally used for generating electricity. It consists of a tank filled

with water kept at some height (50-70 m) and the concentrators focusing energy on it. Thesteam generated is used to run turbines and generate electricity.A solar furnace at Mount Louis can generate up to 3000 oC. It has 3500 small mirrors.

Advantages of Solar Energy Systems:

No fuel or electricity is used to run them They can be installed anywhere on earth where direct sunlight is available. Their upkeep and maintenance require minimal expenditure They are environment friendly and non-polluting

Disadvantage:Very high cost of installation

Solar Cells: The devices capable of converting solar energy into electric energy are calledSolar Cells. The first solar cells could convert 1% of solar energy into electricity. ModernSolar Cells have efficiency as high as 25%. Silicon is commonly used material for solarcells and it is abundant. Today multilayer silicon cells can even convert infrared

radiations to electrical energy achieving high efficiency.

Solar Panel: A standard solar cell of dimension 2 cm 2 produces .7V of potential difference.

Hence a large number of cells are used to generate electricity for practical purposes. Thisarray is called a solar panel.

Solar cells are not so popular because it is very expensive and have low efficiency

Factors adding to the cost of solar cells:Manufacturing special grade silicon is costly

The technology used is expensive Silver is used to connect the cells together Efficient storage system to store energy is unavailable Converting to AC add to the cost


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Applications:They are used as a power source in artificial satellites They are used in installations located at remote areas like TV relay stations, researchstations, traffic lights etc. Used in calculators and toys Finding applications in domestic use too.

WIND ENERGYWind energy is the result of motion in air created due to solar energy. Wind posses kineticenergy which can be used for various useful purposes.

Older uses of wind:(a) Winnowing(b) Sailboats(c) Wind Mills(d) Flying Aeroplanes and Gliders

(e) Entertainment (flying kites etc)

Newer uses:(a) Generating Electricity(b) Doing Mechanical Work

Description of Wind Mill:It consent of a huge fan elected on top of a tower.No. of blades, shape of blades and height from ground are decided on the basis of

wind velocity and other related factors. Principle: The blades are designed to cause a pressure difference between its

different region when wind falls on it. This pressure difference produces a turningeffect on the blades.The speed of rotation of blades vary according to wind velocity.The rotatory motion of the blades are used to rotate a turbine and generateelectricity.

Wind Farms: Generally the electricity produced by a single windmill is not sufficient forcommercial purposes so a large no of windmills are erected on a given area called a windfarm. The output of each wind mill is coupled together to get a larger output.

Limitations of Harnessing Wind Energy:It can only be installed in regions where wind is available throughout the year.The minimum wind velocity required is 15 km/hr.Require a large area of land.High cost of installation.


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Wind Energy is India: India has a wind energy potential of 20,000 MW, but currentcapacity ranges around 1025 MW. Largest wind energy farm is near kanyakumari with acapacity of 380 MW of Energy.

ENERGY FROM WATEREnergy of water is also due to Solar Energy which maintains the water cycle.

Older Uses:Energy of flowing water was used for transporting logs.Water wheel was used for grinding grains.Energy of flowing water is channels in for irrigates.

Energy transformations during water cycle:Solar Energy is incident on water bodies.Solar Energy is used by water vapour to increase its potential energy.

The potential energy of water vapour converts to kinetic energy of water droplets inrain and snowfall.Again as water or melted snow when moving from higher altitude to lower altitudeincreases kinetic energy.

Hydroelectric Power Plants: Hydroelectric Power Plants use the Kinetic Energy of the water flowing down to run turbines and generate electricity. Usually the water is stored inreservoirs to give it high potential energy before used for generating electricity.

(PE)(PE)

Water

Solar Energy

gaining (PE)

Water bodies

Rain & Snow(KE)

Water flowing downIncreasing (KE)

Higher Altitudes (PE)


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Advantages of Hydroelectric Projects:(a) Generates electricity.(b) Can be used for irrigation.(c) Controlling floods.

Disadvantages:(a) Can be established only in Some places.(b) Large arable land area get submerged.

Creates environment problem. problem of rehabilitating people.

plant and animal habitat get destroyed.

Mini Hydro plants: Mine or micro hydroelectric projects can be established only in hillyregion or across Small Irrigation dams. These can only be build in regions where waterfalls through 10 metres.

Ocean Energy Systems: Tidal Energy: Energy possessed by rising and falling tides arecalled tidal energy.A dam is constructed across a narrow opening to the sea. Water moves in to the damduring high tide and out of the dam during low tides through tunnels in the dam wall.

The kinetic energy of the water moving in and out of the tunnel is used to generateelectricity by turbines placed in the tunnels.

Generator

Water atHigh KE

Turbine(Rotational KE)

To river / canal

Output ElectricityWater HighPE

Reservoir

Dam walls


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Reasons why tidal Energy is not popular:The rise and fall of the tides is not of such scale that large scale electricity can begenerated.Dams can only be built at few sites.

Ocean Wave Energy: The kinetic energy possessed by sea waves can be used to generateuseful energy. The total energy due to waves is 2 3 million MW throughout the world.

Reasons for unpopularity of this form of energy:Limited Sites where energy can be fruitfully harnessed.40 MW/Km of coastline is the minimum average energy density required.

Ocean Thermal Energy Conversion (OTEC) Plants: This uses the temperature differencethat exists in ocean water at different depths. A 20 oC temperature difference for a depth of

1000 m is sufficient to run as OTEC plant.In one OTEC system, CFC or Ammonia in liquid form are used. Here the liquids boil at thetemperature existing at the warm ocean surfaces. The vapours generated is used to driveto turbine. The vapours are finally condensed by pumping up colder water from thedepths of sea.

Advantage over other ocean energy systems: OTEC System can be operatedthroughout the year, day and night.

GEOTHERMAL ENERGYIt is one of the few sources of energy which do not directly come from the sun . Itinvolves the use of the thermal energy of the inside of the earth.

Hot Spots: These are areas where molten magma is pushed into due to geologicalchanges. This magma collects at some depth below the earths surface and are called HotSpots.

OCEAN

Water flow

High tide

DAM

GeneratorTurbine

LOWTIDE


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Natural Seysers: When hot spots come in contact with underground water bodies theygenerate steam which may escape to the surface of earth through huge cracks in thestone. This steam and water is at a high pressure and can be used to generate electricity.

Advantages over Conventional power generation:1. It is available 24 hrs throughout the year.2. It is clean and environment friendly.3. Cost of electricity generation is almost half.

Geothermal Energy utilization in India & the world: In India there are limited places where Geothermal energy can be harnessed. It is being done in Madhya Pradesh. USA andNew Zealand have a number of plants based on geothermal energy.

BIO ENERGY:

Biomass is another form of Solar Energy: Plants absorb Solar Energy to store energy inthe form of chemical energy in the process of photosynthesis is which forms the biomass.

The animals down the line in food chain again use this stored energy and further storeenergy is their body mass.

Bio Energy Constituted by:(a) Muscular energy(b) Energy in decaying plant and animal bodies.(c) Energy in wood, crop residues, baggage etc.(d) Energy in animal excreta.

Smokeless Chulhas: Traditional chulhas can only convert 8 10% of the biomass energyto useful energy moreover the burning is incomplete and polluting.Smokeless chulhas are scientifically designed chulhas which promotes fuel efficiency andat the same time is pollution free and hygienic

Destructive distillation of wood:

Wood GasCharcoal

Tar


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When wood is heated in limited supply of oxygen the volatile materials and water isremoved from it. A black fluid called coal tar and wood gas are produced in this process.

The residue left is charcoal .

Charcoal is as expensive fuel: Destructive distillation of 1kg wood yields 250 gm of charcoal. Hence it is considered to be as expensive fuel.

Charcoal is a better fuel than wood : Charcoal burns easily It produces less smoke It has double the calorific value than wood

Biogas: Biomass like Animal dung, Sewage, crop residues, vegetable wastes, waterhyacinth , poultry droppings, Agro Industry wastes etc, can be decayed under the absenceof oxygen (an aerobic condition) to produce a gas rich in methane. This is called biogas .

Biogas plant: The main parts of a biogas plant of any type are(a) Input tank (b) Output tank(c) Digester tank (d) Gas tank

Input tank: This is connected to the digester through a pipe and is used to put inBiomass into the digester tank

Output tank: This tank is used to collect the digested slurry which acts as an excellent

fertilizer.

The digester tank: There are anaerobic bacteria present in the digester task whichdecomposes biomass to produce gases like Methane (75%), carbondioxide, hydrogen andhydrogen sulphide.

Gas tank: The gas tank stores the biogas produced in the digester. From the gas tankbiogas is supplied through outlet pipes to household. Biogas is also sometimes used forelectricity generation.


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TYPES OF BIOGAS PLANT

(a) Floating Gasholder type:

Floating gas holder type biogas plant consists of a steel tank capable of floatingabove a layer of biogas. The main Advantage of the plant is that gas is available at ahigher pressure in this type of plant. It is used were cow dung used as Biomass.

(b) Fixed dome type:

Fixed dome type has a fixed dome shaped gas tank usually made by laying bricks. Itcan use all types of biomass to produce gas.

Fixed dome type biogas plant is cheaper:(i) It can be constructed by laying bricks.(ii) It can accommodate other bio wastes like human excreta besides cow dung.(iii) It lasts longer than floating type plant.

Advantages of producing biogas: Biogas is smokeless It can be used for domestic as well as commercial purposes. It can be used to generate electricity

Gas tank

digester

Inlet tank Outlet tankGas

digester

Gas tank

Inlet tank Outlet tankGas


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It leaves no residue It gives excellent manure as by-product It is a safe method to dispose off wastes.

HYDROGEN AS A FUEL

Advantages:

1. It can be easily produced by electrolysis of water or as an industrial by product.2. It is non polluting as the product of combustion is water.3. It has high calorific value.4. It is used as a fuel in space ships and high temperature flames.

Disadvantages:1. Technical constraints in producing, and usage due to explosive nature.2. Storage and transport is extremely difficult.

Technical achievements in using hydrogen:

1. Fuel cell: Fuel cells produce energy from hydrogen using a controlled reaction andstore it for future use.

2. Some materials are being developed which can absorb hydrogen and mole itavailable for use later.

Alcohol as a fuel : It reacts with oxygen to produce carbon dioxide and water.

It can be manufactured in large quantities by fermentation of sugars. A mixture of Alcohol and petrol is being used in many countries as automobile fuel. Many technical & practical problems prevents it from beings used in a large scale as

fuel.

FOSSIL FUELS

Coal & Petroleum: Coal is the remains of plants that has been fossilized over millions of years whereas petroleum is the fossils of marine animals and plants. Thus fossil fuels areenergy of sun trapped in dead plant and animals.

Coal: Coal deposits are found below the earth. Carbon is the main constituent of coal. The higher the carbon percent in coal the better it is


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The varieties of coal:Peat (most inferior) 27% carbonLignite 28 30% carbonBituminous 78 87% carbonAnthracite (best quality) 97 98% carbon

Coke: Coal is converted to coke by destructive distillation. Coke is used as a reducingagent in metallurgy.Coal generally has a high calorific value.

Petroleum: The main constituents of petroleum are hydrocarbons . It can be said to a complex

mixture of hydrocarbons and compounds of carbon with oxygen nitrogen andsulphur .

They are the dead remains of marine organisms fossilized beneath rocks.

Petroleum was protected by these rocks from seeing into surface of the ocean. Wells are drilled in these rocks to take out petroleum. The petroleum obtained from oil well is called crude oil.

Fractional Distillation:Crude oil is separated into its component by fractional distillation

Fractional distillation uses the differences in boiling points of different fractions of crudeoil to separate them.

Components of petroleum obtained after refining:Non fuels (not readily combustible) Asphalt

Fuel oil (340 0 C)

Diesel (260 0 C)

Kerosene (180 0 C)

Naphtha (110 0 C)

Petroleum (40 0 C)

Petroleum Gas

Heater

Petroleum


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Lubricating oil Paraffin wax

Fuels:(a) Fuel oil: It is used in furnaces and boilers. It is considered better than coal as it

leaves no residue.(b) Petrol: It is mainly used as a fuel in light automobiles.(c) Diesel: It is used as a fuel in heavy automobiles and locomotives generate electricity

in water pumps.(d) Kerosene: It is used for domestic cooking and lighting it is also used as aviation

fuel.(e) Petroleum gas:

Main constituent is Butane; other hydrocarbons like ethane and propane arealso present.

It has high calorific value and is a clean fuel.

It can be liquefied (LPG) under high pressure

Liquefied petroleum gas (LPG): Domestic cooking gas is LPG. The LPG is stored is cylinder and as one opens the

regulator the liquid turns to gas due to decrease in pressure and reaches the burner.

Safety Precautions while using LPG: The valve & stove should be kept in off position when not in use. The stove and the rubber tubing should confirm to standards. Rubber tubings to be examined periodically for cracks.

In case of leakage: do not switch any appliance on or off. open all windows and door should not do any activity that may produce a spark.

Note: To detect leakage; since LPG is odourless lens a foul smelling gas called ethyl mercaptan is added to it.

Natural Gas: Natural gas is a valuable fuel found along with petroleum in oil fields. It mainly contains methane. It supplied through pipe for domestic or commercial use in areas close to oil fields.


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Compressed Natural Gas (CNG): The natural gas is subjected to high pressure andconverted to liquid form called CNG. This makes it easy to transport through pipelines ortankers.

Uses of Natural Gas: It has been used as a fuel in Industries. It has been used in power generation. Used as a source of hydrogen for fertilizer. Being on environment friendly fuel, its use as an automobile fuel is being promoted.

Natural Gas is non polluting : On combustion it gives carbon dioxide water and nopollutants

Note: India has a reserve of 100 billion m 3 of Natural gas reserve.

Calorific value of fuels: Heat liberated in Joules by burning 1gm of a particular fuel iscalled its calorific value.

Q = (C.V.) m f (heat liberated) (calorific value) (man of fuel)

(Joules) (J/kg or J/gm) (kg or 8)

In numerical problems: If we are using this heat liberated to increase the temperature by

( T) of a vessel of mass (M) and water of mass (m) in it then.

Q = m C V T + m C W T when C V and are the specific heat of the vessel and water respectively.

Ignition temperature: When a combustible material is supplied with heat itstemperature rises to a certain minimum value before it starts burning. This minimumtemperature is called its Ignition temperature.

A wet cloth do not catch fire: When a wet cloth is exposed to fire its temperature risesbut dont reach the ignition temperature since the heat energy is being used up in heatingand vaporizing the water. Once the water vaporizes then the cloth is able to reach ignitiontemperature and burn.

Conditions for burning:1. The material should be combustible at a certain ignition temperature2. Heat should be available to take the combustible substance to its ignition

temperature.3. Presence of oxygen.


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Colour of flameIn gas burners or kerosene shows sometimes the fuel burn with yellow flame and sometimes with blue flame.(a) Blue flame: A blue flame shows complete combustion.(b) Yellow flame: Yellow flame is produced when unburnt or partially burned particles

rise up and glow giving yellow color to the flame. In wick type kerosene stove thecylindrical composure can be adjusted to increase oxygen supply.

Improved chulhas: Improved chulhas allow better combustion of fuels by making oxygenavailable in plenty thus they are known as smokeless chulhas. Better combustion alsoensures more heat from fuel.

Controlling Combustion:(a) By reducing oxygen supply:

A thick street of metal is used to cover a coal sigree to put of fire by cutting down the

oxygen supply.(b) By cutting off fuel supply:

When we turn off the LPG regulator we are stopping the fuel supply to put off theflame.

(c) By Lowering Ignition temperature: When we blow off candle we are replacing the hot air around the wick by colder airhence lowering ignition temperature.

Water as a fire extinguisher: Water cuts off oxygen supply by forming an envelope around the fuel. It lowers the ignition temperature of the fuel.

Ensuring efficiency of heating devices: Cleaning of oxygen supply inlets and fuel supplyinlets ensures proper combustion and efficiency of heating devices like stoves etc.

Choosing a good fuel:(a) It should burn at a steady rate (neither fast nor too slow)(b) There should not be any residue left.(c) No polluting substance should be produced on combustion(d) should be easily available at reasonable cost.(e) should have high calorifc value.(f) The ignition temperature should be well above room temperature.(g) It should be controllable.(h) should not be poisonous.(i) should not evaporate at room temperature.

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