Conduction, Convection & Radiation Flashcards
What is Conduction?
Conduction is the flow of heat through matter from places of higher temperature to places of lower temperature without movement of the matter as a whole
Explain a demonstration to show the different conducting powers of various metals:
A match is fixed to the end of each rod using a little melted wax. The other ends of the rod are heated by a burner.
When the temperatures of the far ends reach the melting point of wax, the matches drop off.
The match on copper falls first showing it is the best conductor, followed by aluminium.
What is Convection?
Convection is the flow of heat through a fluid from places of higher temperature to places of lower temperature by movement of the fluid itself
Explain the demonstration to show the how convection works:
It can be shown in water by dropping a few crystals of potassium permanganate down a tube to the bottom of a beaker or flask of water.
When the tube is removed and the beaker heated just below the crystals by a small flame purple streaks of water rise upwards and fan outwards.
What is Radiation?
Radiation is the flow of heat from one place to another by means of electromagnetic waves
Explain the demonstration to show how some surfaces absorb radiation better than others:
The inside surface of one lid is shiny and of the other dull black. The coins are stuck on the outside of each lid with candle wax. If the heater is midway between the lids they each receive the same amount of radiation.
After a few minutes the wax on the black lid melts and the coin falls off. The shiny lid stays cool and the wax unmelted.
How can heat travel in a vacuum?
By radiation as unlike conduction ad convection radiation does not need particles to take place
How does heat reach us from the sun?
Radiation
What happens when radiation falls on an object?
When it falls on an object, it is partly reflected, partly transmitted and partly absorbed; the absorbed part raises the temperature of the object.
What is radiation emitted by?
Radiation is emitted by all bodies above absolute zero
What does radiation consist of?
It consists mainly of infrared radiation but light and ultraviolet are also present if the body is very hot.
Explain how conduction occurs in metals using K.T:
These have a larger number of ‘free electrons’ which wander about inside them.
When one part of a metal is heated, the electrons there move faster (i.e. their k.e. increases) and farther.
As a result they ‘jostle’ atoms in cooler parts, so passing on their energy and raising the temperature of these parts.
This process occurs quickly.
Explain how conduction occurs in non-metals using K.T:
The second process is much slower. The atoms themselves at the hot part make ‘colder’ neighbouring atoms vibrate more vigorously.
This is less important in metals but is the only way conduction occurs in non-metals since these do not have ‘free electrons’; hence non-metals are poor conductors of heat.
What are convection currents?
Streams of warm moving fluids are called convection currents.
They raise when a fluid is heated because it expands, becomes less dense, and is forced upwards by surrounding cooler, denser fluid which moves under it.
How can the inside of a building be kept at a steady temperature.
The inside of a building can only be kept at a steady temperature above that outside by heating it at s steady rate which equals the rate at which it loses energy.
