Transfer of Thermal Energy

Question 1

Demostrating conduction

Answer 1

One foot stands on a thick rug (the rug needs to be on the floor for several hours, to ensure thermal equilibrium, same temp)
The other foot on a tile stoned area
Observe the temperature through your feet

The tile stoned area should feel colder than the thick rug even tho they are at the same temp, this is because heat is easily conducted/transferred away by the tiles, making it a good conductor of heat. And the rug is a good insulator, so when the foot touches the rug the heat isn’t transferred away making it a poor conductor of heat

Question 2

Thermal conduction

Answer 2

Conduction occurs when two solids are at different temps come in contact with each other and the thermal energy transfers by vibrations from the hotter solid to the cooler solid so it balances out

When the substance is heated the solid particles (free electrons) vibrate bumping into each other spreading the heat from atom to atom across the solid this process keeps happen till thermal equilibrium is achieved (when the solid is at the same temp)

Note that this can happen in fluids however is harder to do so when the particles are close but slide past each other
And it cant happen in gases as the particles are widely spread

Conductors tend to be metals the better the conductor the faster it transfers heat, meaning there is a wide range of thermal conductivity

Remember conduction happens in all states of matter EXCEPT vacuum

Question 3

Convection

Answer 3

Convection is the main way that heat travels through liquids and gases NOT SOLIDS
The bottom of the container is heated up so the hot liquid rises to the top eventually cooling down because of the surroundings and cold liquid sinks as its denser and when it reaches the bottom its heated up again and the cycle repeats

Question 4

Demonstrations convection currents

Answer 4

beaker of water and placing a few crystals of potassium permanganate in the bottom of the beaker (in the middle)

When the water is heated at that side, the potassium permanganate will dissolve in the heated water and rise along with the warmed water, revealing the convection current

Question 5

Radiation

Answer 5

All objects give off thermal radiation
The hotter an object is, the more thermal radiation it emits
This is called infrared

The colour of an object affects how good it is at emitting absorbing thermal radiation
- black good absorber good emitter bad reflector
- white bad absorber bad emitter good reflector
- dull good absorber good emitter bad reflector
- shiny super bad absorber super bad emitter good reflector

Question 6

Thermal equilibrium

Answer 6

For an object to have a constant temperature it needs to give off the same amount of radiation that it is absorbing this is called thermal equilibrium
If the object is receiving less energy as it is emitting, it is cooling down
If the object is receiving more energy as it is emitting, it is heating up

Question 7

Greenhouse effect

Answer 7

When the sun rays enter the earths atmosphere, the energy is absorbed by the earth surfaces and remitted at longer wavelengths such as infrared radiation some emitted heat passes through the atmosphere into space some heat is absorbed by carbon dioxide (a greenhouse gas) and is remitted in all directions as a result, the heat may be trapped in the earths surfaces which make the earth hotter

Question 8

Vacuum flask

Answer 8

• made of silver, good reflector bad absorber (reflected back in the flask)
• vacuum, conduction is impossible
• stopper, convection impossible