Chapter 8

This chapter is about the transfer of thermal energy. Thermal energy always flows from a region of higher temperature to a region of lower temperature.

Transfer of Thermal energy:
- conduction
- convection
- radiation

Conduction
I learnt 2 important ponts of it :

1) Thermal energy flows through the medium itself. The transfer of thermal energy without any movement of the material medium is called conduction.

2)Different materials conduct heat at different rate.

How does conduction work in a solid?

Metals contain many free electrons which move randomly between the atoms. When thermal energy is supplied to one end of it, the particles at the hot end will vibrate vigorously. It will then collide with the neighbouring particles, making them vibrate as well.
The free electrons in it gain kinetic energy and thus move faster. These fast moving electrons will then spread to the cooler part of the metal, colliding with the atoms and transfering the kinetic energy to them.

Conduction in liquids and gases?

The particles in liquids and gases are spaced further apart than in solid, causing collisions between particles to be less frequent. Thus, gas is a poor conductor of heat and solid is a good conductor of heat, liquid being in between.

Common applications of conduction

Uses of good conductors of heat

1) Cooking utensils
2) Soldering iron rods
3) Heat exchangers

Uses of bad conductors of heat

1) Handles of appliances and utensils
2) Table mats
3) Sawdust
4) Wooden ladles
5) Woollen clothes
6) Fibreglass, felt and expanded polystyrene foam