Volume B Chapter 25 Transmission of Heat

Oh no! You will spoil the flask if you put cold water in it. After this, the flask cannot be used to keep water hot anymore. Myth or Truth?

Why are the handles of saucepans usually made of plastic?

Why is food packed in styrofoam boxes?

Cooling fins at the back of refrigerators. Why are they always painted black?

Heat is a form of energy that is transmitted from a region of higher to lower temperature . Heat Moves!

IN 3 WAYS… CONDUCTION CONVECTION RADIATION Heat Moves!

They are three processes of heat transfer shown in the picture. 1 represents 2 represents 3 represents conduction . convection . radiation .

Conduction is transmission of heat through a material from the hot regions to the cold regions without any visible movement of the material. CONDUCTION

Conduction of heat through solids Observation : Observe the lengths of wax that have melted on the different rods in a given interval of time . Wood Iron Aluminium Copper

Good & Bad Conductors of Heat Good conductors Poor conductors (insulators) Silver Copper Aluminum Brass Iron Lead Stainless Steel Vacuum Air Styrofoam Body fat Cork Water Glass

. Try This : Fill in the table appropriately Brass Wood Aluminium Air Foam Copper Iron Water Cotton Plastic Mercury Gold Good Conductors Good Insulators

. ANSWER : Fill in the table appropriately Brass Wood Aluminium Air Foam Copper Iron Water Cotton Plastic Mercury Gold Good Conductors Good Insulators (or Bad Conductors) Brass Aluminium Wood Air Copper Iron Foam Water Mercury Gold Cotton Plastic

Convection is the transmission of heat through a fluid (liquid or gas) from the hot to the cold region by the circulating movement of the fluid. CONVECTION cool (higher density) hot (lower density) liquid or gas

CONVECTION IN LIQUIDS See movie

CONVECTION IN GASES

Application of Convection Sea and Land Breezes

Application of Convection Sea and Land Breezes

Application of Convection Hot Water System

Application of Convection Air- Conditioners

QUIZ TIME!!

Q1. Which of the following is a good conductor of heat? A. Water B. Oxygen C. Wood D. Aluminium

QUIZ TIME!!

Radiation is the transmission of heat from one place to another by means of infra-red radiation which can travel through vacuum or air Radiation

Rate of Emitting (giving out) and Absorbing Heat by Radiation is affected by: (a) surface temperature (b) colour and texture of the surface (c) surface area Radiation

Radiation Why does the cork on the dull black surface fall off first? Ans: Dull black surfaces are good absorbers of heat, thus it melts the wax faster

Application of Radiation Good Emitters Poor Emitters Cooling fins at the back of a refrigerator painted dull black A shiny metal teapot and aluminum foil keep contents warm

Application of Radiation Good Absorbers Poor Absorbers Solar heating panels are painted in dull black paint to absorb heat from sun Houses in hot countries are painted in white or light-coloured paint , to keep them cooler . Light colours are chosen for clothes and cars in hot weather

Application of Radiation

They are three processes of heat transfer shown in the picture. 1 represents 2 represents 3 represents conduction . convection . radiation .