TRANSFER OF HEAT CONDUCTION CONVECTION RADIATION

CONDUCTION THE TRANSFER OF HEAT IN SOLIDS FROM ONE PARTICLE TO ANOTHER WITHOUT THE ACTUAL MOVEMENT OF PARTICLES. EXPLANATION BASED ON KINETIC ENERGY IN SOLIDS MOLECULES ARE CLOSELY PACKED WHEN HEAT IS GIVEN AT ONE END, MOLECULES ABSORB ENERGY THEY START VIBRATING. THEY COLLIDE WITH THE NEIGHBOURING PARTICLES THE NEIGHBOURING PARTICLES START VIBRATING THERE IS A TRANSFER OF HEAT ENERGY THIS CONTINUES TILL THE END IMPORTANT: MOLECULES DO NOT TRAVEL

CONDUCTION REMEMBER AIR AND WATER ARE BAD CONDUCTORS OF HEAT GOOD CONDUCTORS (most metals) BAD CONDUCTORS (glass, asbestos, wood, plastic) REMEMBER AIR AND WATER ARE BAD CONDUCTORS OF HEAT

APPLICATIONS Soldering iron: The soldering iron is made of copper, because it is a good conductor of heat. Conducts the heat away quickly. Mercury is used in thermometer: because mercury is a good conductor of heat and is very sensitive to small heat changes. Animals in cold regions have thick fur: fur traps a lot of air. This is a bad conductor of heat. So heat energy does not flow out from their bodies. New quilt is warmer than an old quilt: the old quilt after usage, the cotton inside are compressed. So there is no trapped air. Whereas, in the new quilt, the cotton is puffed which contains air which is an insulator.

convection LIQUIDS AND GASES TRANSMIT HEAT MAINLY BY CONVECTION WHICH IS HEAT TRANSFER BY THE ACTUAL MOTION OF THE FLUID ITSELF. CONVECTION CURRENTS KEEP THE FLUID STIRRED UP, WARMER FLUID MOVING AWAY FROM THE HEAT SOURCE AND COOLER LIQUID MOVING TOWARDS THE HEAT SOURCE. PRACTICAL APPLICATIONS OF CONVECTION CURRENTS Chimneys fitted in factories: they are fitted to remove fumes and smoke. Since they are less dense than air, they rise up through the chimneys. installation of a freezer: freezer is mostly situated at the top. Cold air being heavy, sinks down to cool the things kept at the lower part. The heat released makes the air at the bottom warm and rises up. Thus convection currents help us.

radiation BASIC THINGS TO KNOW: energy from the sun passes through space it is not by conduction as air is a poor conductor it is not by convection because convection can happen only when earth is warmed therefore the energy radiated has be in the form of radiant energy. Radiant energy is in the form of electromagnetic waves. This includes, radio waves, infra red waves etc. SUPPOSE WE HAVE AN AUTOMOBILE PAINTED BLACK. ON A HOT DAY, IT REMAINS HOTTER THAN ITS SURROUNDINGS, BUT AT NIGHTFALL THEY COOL FASTER. SO A DARK OBJECT THAT ABSORBS RADIANT ENERGY MUST EMIT A LOT AS WELL.

PROPERTIES OF THERMAL RADIATIONS Travels through vacuum radiations travel in straight lines travel with the speed of light they do not heat the medium they pass IMPORTANT TO REMEMBER: BLACK BODIES ARE GOOD ABSORBERS AND GOOD EMITTERS OF HEAT APPLICATIONS OF BLACK AND WHITE SURFACES choice of clothes: we wear white clothes during summer because white absorb less heat. Whereas we wear black colored clothes during winters because they absorb more heat. petrol storage tanks: it is painted with aluminium paint which gives a silvery appearance. White is a bad absorber of heat. So it will reflect heat by which petrol inside the tank will be kept cool.

THANK YOU FOR YOUR PATIENCE