Physics p6 - Transfer of thermal energy

2.3 (a) Conduction Core  Describe experiments to demonstrate the properties of good and bad conductors of heat.  Explain heat transfer in solids in terms of molecular motion. > Comparing four good thermal conductors between copper, aluminium, iron and steel. Firstly, rods are coated with a thin layer of wax attached to the tank carrying the boiling water. Ten minutes after, the boiling water has been tipped into the tank, the length of melted wax shows which material is the best conductor. > This experiment shows that water is a poor thermal conductor. The water at the top of the tube can be boiled without the ice melting. Here in this experiment, the gauze helps sink the ice.  

----> All particles are made up of tiny , moving particles called atoms or moelcules. The higher the temperature, the faster these particles move. After a period of time, heating one end of a piece of metal will eventually heat the other side too. It will become too hot to touch. Thermal energy is transferred from the hot end to the cold end as the faster particles pass on their extra motion to the particles all along the bar. Thermal enrgey is transferred by conduction 

(b) Convection Core  Recognise convection as the main method of heat transfer in fluids. Describe experiments to illustrate convection in liquids and gases.

Model of an atom 

Convection- is a main method for heat transfer in fluids. They are poor thermal conductors, but are free to circulate they can carry thermal energy from one place to another very quickly. 

In this experiment, the bottom of the beaker is being gently heated in one place only. As the water above the flames becomes warmer, it expands and becomes less dense. It rises upwards as cooler,denser water sinks and displaces it (pushes it out of the way). The result is a circulating stream, called the convection currnet. Where the water was heated, it's particles gain energy and vibrate more rapidly. As it circualtes faster, they transfer energy to the other parts of the beaker. 

*Note: convection does not occur if water is heated from the top. The warmer, less dense water stays on top.  

---potassium permanganate crystals to colour water

Convection in a liquid 

Convection in air

-Heated by the sun, the warm air rises above the equator as it is displaced by cooler, denser air sinking to he north and south. The result is big convection currents in the earth's atmosphere. These cause winds across all oceans and continents. Convection also cause the onshore and offshore breezes which sometime blow at the coast during summer 

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