08 Thermal Processes

What is heat?

A flow of energy from a higher temperature region to a lower temperature region, which continued until the to regions have reached thermal equilibrium.

What is thermal equilibrium?

A state in which two or more objects have the same temperature and that there is no bet transfer if energy between them

How do particles use conduction to transfer energy?

Particles at the heated end gain kinetic energy and vibrate more vigorously. They collide with neighbouring particles, causing them to vibrate more vigorously as well. This process continues until the particles at the cooler end are also set into vigorous vibration.

How does conduction in metals works?

The electrons at the heated and gain linetic energy and move rapidly. They then collide with particles in the cooler parts of the metal and transfer their kinetic energy in the process. This continues until the larticles at the cooler end are also set into vigorous vibration.

Why are metals better conductors of heat.

In metals, there are free electrons to have a faster rate of heat transfer than nonmetals through the process of free electron diffusion. Hence, metals conduct thermal energy more wuickly than nonmetals.

Explain how the concept of thermal energy is applied in a stove.

Metals like aluminum and steel are good thermal conductors. Through vibrations and collisions of particles as well as free electron diffusion, they increase the rate of heat transfer by conduction from the stove to the food. This ensures that the food is cooked in a shorter time.

What is the difference between convection and conduction.

Convection involves the bulk movement of the fluid medium due to changed in densities whereas conduction involves the vibration of particles only.

Describe a convection current

The air below is heated, expands, becomes less dense and rises. The colder denser air above sinks to replace the warm air and gets heated in turn. A convection current is set up until thermabl equilibrium is reached.

What is radiation.

The transfer of thermal energy in the form of electromagnetic waves without the aid of a medium

What is conduction

The transfer of thermal energy through a medium from one particle to another

What is convection

A process of energy transfer by means of convection current of a fluid due to a density difference.

What factors affect the rate of thermal radiation

Colour and texture, surface area, surface temperature

Using concepts of heat transfer, explain why the suit of an astronaut is shiny and white.

White and shiny surfaces are poor absorbers of thermal radiation. This reduces the rate of heat transfer by thermal radiation from the dun to the astronaut. This ensures that the astronaut remains cool.

A bunsen burner boils the top of a test tube while the ice at the bottom melts slowly, why is this?

Since heated water above expands, becomes less dense and remains above the cooler, denser water below, convection currents are not formed. Since water is a poor thermal conductor there is a low rate of heat transfer by conduction from the flame to the ice. The ice melts slowly.