Chap 10 Transfer of Thermal energy Flashcards
What are the 3 processes in which thermal energy is transferred?
Thermal energy is transferred by conduction, convection and radiation.
What is conduction?
Conduction is the process of thermal energy transfer without any flow of the material medium.
How does conduction work in a rod?
When thermal energy is supplied to one end of a rod, the particles at the hot end vibrate vigorously. These particles collide with neighbouring particles, making them vibrate as well. The kinetic energy of vibrating particles at the hot end is transferred to neighbouring particles.
What is the main difference between conduction in metals and non-metals.
Metals contain free electrons which move randomly between atoms and molecules while non-metals do not have free electrons.
Why are metals good conductors of heat?
In metals, another much faster mechanism of thermal energy transfer takes place at the same time which is free electron diffusion. The free electrons gain kinetic energy and move faster. The fast-moving electrons then diffuse into cooler parts of the metal, transferring kinetic energy to particles and electrons it collides with.
Describe conduction in liquids and gases.
The process of conduction is inefficient in liquids and gases as the liquid particles are further apart and collisions of particles are less frequent and lesser in gases. Thus, transfer of kinetic energy from fast-moving molecules to neighbouring molecules is slower.
What is convection?
Convection is the transfer of thermal energy by means of currents in a fluid.
How does a convection current form in fluids?
When fluids are heated, they expand and become less dense. The less dense fluids tend to rise from the heating source. Cooler fluids, being more dense, sink to replace the less dense, warmer fluids. This movement of fluid due to a difference in its density sets up a convection current.
What is radiation?
Radiation is the continual emission of infrared waves from the surface of all bodies, transmitted without the aid of a medium.
What are the 2 factors affecting the rate of infrared radiation?
Colour and texture of the surface and the temperature of the surface.
One example of a good absorber/emitter of infrared radiation and one example of a poor absorber/emitter of infrared radiation
Dull, black surfaces (Good absorber/emitter). Shiny, white surfaces (Poor absorber/emitter).
