Conduction

The Concept of Conduction of Heat

Explain the concept of conduction of Heat Conduetion is the wansfer of heat energy through solids, for example, metals, Generally solid substances contain particles which are close together. Each particle vibrates at one position but cannot move to another position Solid matenals differ greatly in their ability to conduct HEAT Good and Bad Conductors of Heat Identify good and bad Conductors of Heat Solid materials differ greatly in their ability to conduct HEAT.

Good conductors These are the substances which allows the passage of heat energy easily example all metals. Metals contain tiny particles called electrons (particles that carry electricity through metals) which are ffee to move inside the metal and carry energy from hotter places to colder places, Bad conductors These are materials which does not allow the passage of heat and electricity e.g Non ~ metals, woods

Goon CONDUCTOR AD CONDUCTOR

• Silver + Glass

© Aluminum + Wood

• Brass = Asbestos

+n + Water

• Copper + Ae
• Stet

How to Minimize Heat Losses due to Conduction Explain haw to minimise Heat lasses due to Conduction There are some simple ways to reduce heat loss, including fitting carpets, curtains and draught excluders Heat loss Uarough windows can be reduced using double glazing. The gap between the two panes of glass is filled with air Heat loss through conduction is reduced, as air is a poor conductor of heat, Heat transfer by convection currents is also reduced by making the sap is very narrow.

Heat loss through walls can be reduced using cavity wall insulation. This involves blowing insulating an material ante the gap between the brick and the inside wall, which reduces the heat loss by conduction, The material also prevents air circulating inside the cavity, therefore reducing hoat loss by convection.

Knowledge of Conduction in Daily Life Apply knowlesige of conduction in daily life The difference in conductivity of various materials ean be demonstrated using Edser's apparatus on ep) 3 li} i a I ao, .

fixed to the bottom ofthe can, poured inside ihe copper ca, est wil be passed along the rods by conduction: Afr stone St wil be observed ae was cotted the vod wil 'mdt and eve dow the rods. Note how far along the rods the wax has melted when the apparatus reaches a steady state.

This indicates tht the’ materials from which the rode ‘wre ads. Rave iene. dermal than the rest. Conduction of Heat Energy through Liguids

• All Houids expect mercury and gases are poor conductors of heat

Conveetion

The Concept of Convection of Heat

Convection is the transfer of Heat through the fluids (Liquids or Gases) convection { current &. potassium permanganate Convection in Fluids in Terms of Kinetic Theory of Matter Explain convection in fluids in terms of kinetic theary of matter ‘Convection currents are the currents of Liquid that move from the Bottom to the top ofthe liquid The heated liquid expands and becomes less denser and so can float upwards and replaced by

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— OC i bein Convection in gases. Convection air current occurs due to the unequal Heating of the Barth's atmosphere by the sum (Thus current called strong convection euent) cecler atoms move to the bottom 353005 0, Sooo 6 ?oE200 4 Q"ooo 0+0+0+Q-0” a rise heat How to Minimize Heat Losses due to Convection in Daily Life Explaia how t:minieise hoot lares dato comvec ion ® dll Ff When you understand the effects of cold water on the body, and how the body responds, you ae

far more prepared to make lifesaving decisions, either for yourself or in a rescue situation. (eS ain gale, simple’ ie Gedy icing ia mab ‘sot one tempene (homeostasis) through a balance of heat loss and heat gin, Body hea is nomally gained through activities such as exercise and shivering, and also with the application of external heat sources such as heat packs.

Convection is the process of air or water flowing by the skin and carrying away body heat. I's convective heat loss that you try to prevent by staying as still as possible in the water. Staying still, the boundary layer of water next to the skin is heated by the body and remains undisturbed.

If you move around im the water, you disrupt that boundary layer of warmer water, and that increases heat loss. Once a body has been in cold water for an extended period of time, most ofthe skin is cool with little blood flow. However, there are critical areas that are lighter (warmer) than the surrounding tissue, Tis is because blood is flowing through major blood vessels, which are near the skin surface, These areas in the neck, armpits and groin are areas of high heat transfer. That means

that these areas have high heat loss in the cold but allow heat gain in the heat. This is why, in a rescue scenario, the most effective rewarming often consists ofapplying extemal heat directly to the armpits as well asthe chest.

AAs final note, it's important to realize that the activity of swimming (which is naturally thought ‘of as producing a heat GAIN), in cold water conditions will result in increasing the blood flow to blood vessels close to the skin, and because of conduction and convection, it can actually increase the rate of heat LOSS and expedite the onset of hypothermia Knowledge of Convection to Daily Life Apply knowledge of convection o daily ife

Domestic hot water system

• Conveetion currents are used to circulate hot water from a boiler in a domestic hot water

system. The system consists oPaboiler B, a hot water storage tank, Hand cold water supply tank (cistern) C all connected by pipes.

• When water is heated (electrically or by fire) at the bution of the boiler, it expands and

become less dense, and so rises to the top.

• The hot water in the boiler passes through the outlets at the top of the boiler into the

upper part of the hot water storage tank

• The lower portion of the storage tank is filled with cold water from the cistern, which is

high enough to drive the hot water out when the hot water tap T is open.

• The eistern is fied with a ball-cock which maintains the level of water in the cistorn by

allowing water in when the level falls. from mains from maine ee — header tank ear tank i hot water taps ’ 5 a inet heated eyleder y= con wane tps raxators L]

Radiation

The Concept of Radiation

Explain he concept of radiation Radiation is transfer of heat energy from one point to another without the requirement of any material medium, The stars including the sum illuminate the world by radiation Radiant energy from the sun Reaches the Earth through the Vast empty space (vacuum) existing between the atmosphere and the sun This energy travels with the speed of light and has similar properties to light ie. Radiant energy

can be veetedsheorbed aad Transit The iy wie at tna gy becomes heel up anit epee Good Absorbers and Emitters of Radiant Heat Thetmopile isan instrament which convents radiant cngy (sant heat ent) into electrical energy ifthe seis of ho Cnnooounle ee connect ow anhranoneet by eonmeotian wire cucent electric lamp.

Fe air — rh : (ps \ { io} sie \ Z / oo L The ‘Temperature of the body. 2 The Nature of surface the body

• The surface area for the body

To demonstrate the fact that the amount of Heat energy radiated from a body depends on the nature and area of its surface (Leslie's cube) can be used. ‘The figure below shows Comparison son of Radiant energy fiom different ~ substance

• Leshe’s cube is a cube — shaped metal Box which has Three of its sides painted with

different colours ¢ g Green, Black and Grey.

• One side is highly potished serve as a reflecting surface
• The cube is placed on a Tum table R and Maintained Hot by Running steam into it.
• Thermopile, T connected to a galvanometer G is placed at a fixed distance from the eube

by Turning the Turn table

• The black side of the cube will produce the largest deflection of the Galvanometer G.

While the polished surface will produces the leats deflection,

• The alfemative demonstration of the absorption of radiant Heat by a surface can be per

formed by using two tiny plates and Ban sem burner. Heat Losses due to Radiation Mice Ret ei Yo raion The voc Nas: ra designed by sir James Dewar for purpose of stoning oudenser sri the guid state Now days used for keeping liquids hot over a period of Time. It would also keep liquids Cold for slag tine qf plastic stopper i hot liquid deuble-nalied glass bottle cater case thin sivered walls i of gles cork te hold flosk in place

The vacuum flask consist ofthe double walled ps vested with « vacuum between the wai Th asa ths mc aad TRE ee nection, esi raliton of Hest energy ay