Thermal Energy is transferred only when there is a difference in temperature. Thermal energy always flows from a region of higher temperature to a region of lower temperature.
How is thermal energy transferred?
Most objects near the barbecue pit are not in direct contact with the burning charcoal. So how is the thermal energy from the red hot charcoal transferred to these objects?
Thermal energy is transferred by ant of these three processes: conduction, convetion and radiation.
Conduction
What is conduction?
If one end of a metal rod is heated with a flame, the other end will also get heated up after a while. Fromt this, we can see that thermal energy is transferred from one end of the metal rod to the other. The transfer of thermal energy through a medium, without the medium moving, is called conduction.
Conduction is the process of thermal energy transfer without any flow of the material medium.
Experiment 1:
Objective: To investigate the transfer of thermal energy through solids
Apparatus: bath, rods of the same dimensions but of different materials, stopwartch
Procedure:
1. coat the parts of the rods that are on the outside of the tank evenly with melted wax
2. pour boiling water into the bath, so that the ends of the rods are submerged
3. record the length of wax that melts in a given interval of time for each of the four rods.
Observation: the wax melts furthest along the copper rod, followed by iron, glass and wood.
In this experiment, thermal energy is transferred from a region of higher temperature to a region of lower temperature. The wax on the rods melts as thermal energy is transferred from the boiling water towards the colder end of the rods. But the length of melted wax on each of the four rods is different. In other words, the lenth of unmelted wax is shortest for the copper rod and longest for the wooden rod.
2 important conclusons:
1. thermal energy flows through the material of the rods without any flow of the material itself. such a transfer of thermal energy without any movement of the material medium is called conduction
2. different materials conduct heat at different rates. SInce the length of unmelted wax is shortest for copper and longest for wood, it can be concluded that copper is a good conductor of heat and wood is a poor conductor of heat. Another term for poor conductors of heat is insulator.
How does conduction work?
All solids (metals and non metals) are made up of tiny particles called atoms and molecules. The difference between metals and non metals is thst metals contain many free electrons which move randomly between the atoms or molecules, while non metals do not have such free electrons. WHen a metal and non metal is heated from one end, with thermal energy supplied to one end of the rod, the particles will collide with neighbouring particles, making them vibrate as well. Thus, the kinetic energy of the vibrating particles at the hot end is transferred to the neighbouring particles. The process of transferring thermal energy from the hot end to the cold end by atomic or molecular vibration take place in both metal and non metal. In this process, there is no transfer of particles. it is quite slow to transfer thermal enrergy this way. however, in metals, another much faster mechanism of thermal energy transfer takes place at the same time: free electron diffucsion. When the copper rod is heated, the free electrons in the copper gain kinetic energy and move faster as a result. These fast moving elecrtrons then diffuse or spread into the cooler parts of the metal and transfer their kinetic energies to them. this explains why good conductors like metals are cpable of transferring thermal energy much faster than insulators.
