4 Thermal energy Flashcards
Where is thermal or heat energy stored in?
It is stored in ‘hot’ matter.
How do we know if something has thermal energy?
If it is above absolute zero.
What is heat in relation to particles?
It is the kinetic energy of the tiny particles that make up all matter which produces the effect which we call heat.
In which way is thermal energy transferred?
From a place that is hotter, to one that is colder.
What are the ways in which thermal energy transfer can take place?
- Conduction.
- Convection.
- Radiation.
What is thermal conduction?
It is the transfer of heat through a substance by the vibration of the atoms within a substance. The substance itself does not move.
What is an example of thermal conduction?
Cooking kebabs on a barbecue with a metal skewer. The metal over the burning charcoal becomes hot and the heat energy is transferred along the skewer by conduction - ultimately heating and cooking the chicken.
What is a good example of a thermal conductor?
Metal, because it conducts thermal energy quite well.
What is a good example of a thermal insulator?
Wood, because it doesn’t conduct thermal energy very well.
How does conduction take place in reference to particles?
In a hot part of a substance, the particles have more kinetic energy. The more energetic particles transfer some of their energy to particles near them. Therefore, these particles gain energy and then pass energy to particles near them. This energy transfer goes on throughout the substance, and this process takes place in all materials.
Why does conduction take place faster in metals in reference to particles?
This is because metals have free electrons that can move easily throughout the structure of the metal, making the transfer of energy happen faster.
Explain the practical that is in reference to how well different metals conduct heat.
As the heat passes along the roads, the petroleum jelly holding the drawing pins in place melts and they drop off in sequence. This experiment also shows that copper conduct heat better than steel because the drawing pins attached to the copper rod drop-off sooner than those attach to the steel rod, this world should be the same diameter, and the drawing pins placed at the same distance is from the heat source for this to be fair test.
What are the two things that you need for conduction?
1) Contact.
2) Energy (temperature) difference.
When does conduction stop?
When both temperatures are equal.
What is convection?
It is the transfer of heat through liquids and gases by the upward movement of warmer, less dense regions of fluid.
What is a convection current?
The heated water expands, and becomes less dense than the colder surrounding water, so it floats up to the top of the glass beaker. Colder, water sinks to take its place, and is then heated too. At the top, the warm water starts to cool, becomes more dense again, and will begin to sink, so circulating current is set up in the water. This is called a convection current.
Explain the experiment for convection currents which uses a potassium manganate crystal in the water.
The water is heated just under the purple crystal and the crystal colours the water as it dissolves which lets you see the movement of the water. Which is a convection current.
Explain the experiment for convection currents which uses a candle.
Air is warmed by the candle and floats up the chimney on the right. The left chimney is drawing down the chimney on the left.
Explain the experiment with convector heaters.
1) Cold air is drawn in at the bottom.
2) Through the bottom vent.
3) the cold air is then heated.
4) Through the top vent.
5) Warm air is then pushed out of the top.
How is convection used in ovens?
In many cooking ovens, the heating element is placed at the bottom of the oven. It heats the air near to it, and this air rises by convection. The top of the oven is generally warmer than the bottom, so you can cook food at different temperatures. However, many cooker ovens now use fans where hot air is blown into the oven and provides an even temperature throughout the oven.
Which fluids both allow heat transfer to take place by conduction?
Air and water, even though they are not good thermal conductors. Rather, insulators.
Why are these fluids insulating properties put to good use?
AIR -Woollen clothing keeps you warm because air gets trapped in the fibres. The trapped air is heated by your body and forms a warm insulating layers that stops you from losing heat.
WATER - In the same way, a wetsuit keeps a diver warm because a thin layer of water is trapped next to the divers skin.
How is convection responsible for in terms of the environment?
Off-shore breezes.
On-shore breezes.
Lightning.
How is convection responsible for off-shore breezes?
The air over the warmer sea floats up causing cooler air to flow towards the sea. The land cools down more quickly than the sea at night.
