Unit 9: Transfer of Thermal Energy Self Learning Package Click here to proceed to next page

Topics to be covered Thermal Energy and Heat Conduction Convection Radiation

Textbook References Marshall Cavendish Textbook – Chapter 10 GLM Red Book – Unit 9

Thermal Energy and Heat Recall from the previous Unit the concept of “internal energy”, i.e. the amount of thermal energy stored within a substance Thermal energy can be classified under two different categories: 1) Thermal Energy which is not moving (i.e. within a substance) is called “internal energy” 2) Thermal Energy which is moving is called “Heat”

Heat Heat always travels from a hotter region to a colder region Heat travels through 3 different means: 1) Conduction 2) Convection 3) Radiation

Conduction In solids, heat is transferred mainly through conduction Recall from the previous unit: particles in solids vibrate about fixed positions When heated up particles vibrate even more vigorously When this happens, they collide with neighbouring particles, transferring kinetic energy to them, and making them vibrate vigorously as well This way, heat flows from a hotter region of the solid to a colder region of the solid

Conduction Metals conduct heat better than non-metals This is because when a metal is heated up the free electrons at the hotter region gain more kinetic energy and travel to the cooler regions, transferring kinetic energy there This process is called free electron diffusion

Convection Convection can only occur in fluids (Note: Fluids = Liquids and Gases) When a fluid is heated, it expands and becomes less dense Due to the decrease in density, it will rise, while cooler, denser, parts of the fluid will sink This results in the formation of convection currents

Radiation When an object is hotter than its surroundings, it gives out radiation (i.e. it is an emitter of radiation) When an object is colder than its surroundings, it absorbs radiation (i.e. it is an absorber of radiation) Unlike conduction and convection, no medium is required for radiation to take place (i.e. radiation can occur even in a vacuum)

Radiation 3 factors affect the rate of radiation 1) The greater the difference in temperature between the substance and the surroundings, the greater the rate of radiation 2) The greater the surface area of the substance, the greater the rate of radiation 3) White/Shiny surfaces have less radiation, black surfaces have more radiation

Summary Heat is Thermal Energy which is moving from hotter region to colder region Conduction Convection Radiation

Assignment Click on the link below to complete Part 2 of your June holiday assignment. Note there is also a Part 1 (Unit 8). s/d/14Y2JHf5AOZ3QXd_vpQCC2L9S56brHl2frs3E N1mYWbA/viewform?usp=send_form s/d/14Y2JHf5AOZ3QXd_vpQCC2L9S56brHl2frs3E N1mYWbA/viewform?usp=send_form Note: you need to login to your preshigh account Due date: 9 July 11:59 pm (Press “Esc” to end this presentation)