[PHY] Chapter 9 - Transfer of Thermal Energy

DARRELL ER (COPYRIGHTED) © TOPIC 9: TRANSFER OF THERMAL ENERGY

CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE

TRANSFER OF THERMAL ENERGY CONDUCTION CONVECTION RADIATION KEY CONCEPT

LAW OF THERMAL ENERGY - Thermal energy flows from a region of higher temperature to a region of lower temperature - Can be transferred through conduction, convection or radiation LAW OF THERMAL ENERGY

Conduction in solid When one part of the solid is heated, the atoms there gain kinetic energy and vibrate faster. These atoms collide with their less energetic neighbours, resulting in a transfer of kinetic energy from the hotter area to the colder area. This process continues until all the particles possess the same amount of thermal energy. Conduction in metals Conduction is far better in metals than non-metals due collision of vibrating atoms & the movement of free electrons. When heated, the free mobile electrons gain energy and move faster. Since free electrons are free to travel in the spaces between the atoms to transfer energy, conduction occurs much faster in metals. CONDUCTION CONDUCTION Conduction is the process by which thermal energy is transmitted through a medium from one particle to another. There is no net movement of atoms during the process of conduction. Thermal energy is transferred through the increase in vibrational kinetic energies of the atoms. SOLID, LIQUID, GAS Solids are better conductors of thermal energy than liquids and gases. Molecules are packed closer together in solids than in liquids and gases, thus kinetic energy can be transferred more quickly. CONDUCTORS - Cooking utensils - Heat sinks in electronic equipment conduct thermal energy away to avoid overheating INSULATORS - Wooden ladle used to stir hot things - Kettles, saucepans and electric irons have plastic or wooden handles

CANDLE WAX EXPERIMENT As heat energy is transfer from the hotter end of the rod to the other end through conduction, the nail at A will drop off first, followed by B then lastly, C. ANOTHER EXPERIMENT: We can also observe the rate of conduction across different materials through this experiment too!

Convection in liquid When part of a liquid is heated, it expands in volume, becoming less dense than the surrounding liquid and rises. The cooler and denser liquid sinks. The cooler liquid in turn gets heated up and rises, resulting in a continuous convection current. Convection in gas The hot air near the heat source rises as it expands and becomes less dense, while the cooler and denser air at the top sinks. The cooler air now gets heated up and rises, resulting in a continuous convection current. CONVECTION CONVECTION Convection is the process by which thermal energy is transmitted from one place to another by the movement of heated par