Unit 3 - Lesson 11: Heat Transfer (Conduction, Convection, and Radiation) Flashcards
(54 cards)
Why are fossil fuels bad for the environment?
Fossil fuels produce a lot of CO2. They are also going to run out, so reducing their use is essential.
What three methods can heat be transferred with?
Conduction - Heat transferred between particles in a solid.
Convection - Heat transferred between particles in liquids & gases.
Radiation - Heat transferred by Infrared waves. Can move through solids, liquids & gases.
Some objects emit heat (thermal energy) and others absorb it. Give an example for an object that emits heat and an object that absorbs heat.
An object that emits heat: Radiators.
An object that absorbs heat: Solar Panels.
The bigger the temperature difference is between regions, the (faster/slower) the heat is transferred between the thermal energy stores of the object and its surroundings.
The bigger the temperature difference is between regions, the faster the heat is transferred between the thermal energy stores of the object and its surroundings.
Fill in the blank. Heat during conduction and convection is the result of the …………………….. of molecules (or any particle).
Heat during conduction and convection is the result of the MOVEMENT of molecules (or any particle).
Explain why something large and cold can still have more heat energy than something small and hot.
Heat energy is transferred by conduction or convection through the movement of particles. A large object will have more particles than a smaller one. So, even though each of these particles has less heat energy (because they’re not moving as much), the sheer number of them gives the large object a greater total amount of heat energy.
What type of heat transfer does the statement describe? Convection, radiation or radiation?
The movement of currents (of molecules or atoms) through a liquid or gas.
Convection
Gliders are aircraft that don’t have engines. They work by using natural (convection/conduction). They are pushed up by (hot/cold) air near the Earth’s surface (heated by the sun’s radiation).
Gliders are aircraft that don’t have engines. They work by using natural convection. They are pushed up by hot air near the Earth’s surface (heated by the sun’s radiation).
You’re on a mountain expedition. Your guide has given you hot chocolate in a thermos flask. Explain why the drink stays warm.
A thermos is one bottle inside another. The gap between the two bottles is a vacuum (free space i.e. doesn’t have anything in it). Because there are no molecules in a vacuum, none of the heat can escape the thermos by conduction. This isn’t a perfect system, though, because a little bit of heat radiation does escape. IR radiation can move through a vacuum.
Air is a poor conductor of heat. Use this fact to explain why a big puffer jacket helps keep you warm.
The padding is full of air pockets. Air is a poor conductor of heat, so the heat gets trapped in the jacket (next to you). The pockets of air are small, meaning convection is prevented.
Why do all objects emit heat?
All objects emit heat because their particles are moving. The more movement, the more heat.
Does an object that’s hotter than its surroundings emit more or less IR than it absorbs (as it cools down)?
An object hotter than its surroundings emits MORE IR than it absorbs (as it cools down) .
Does an object that’s colder than its surroundings emit more or less radiation than it absorbs (as it warms up)?
An object colder than its surroundings absorbs MORE radiation than it emits (as it warms up). I.E. It emits less radiation than it absorbs.
What is thermal radiation?
All objects emit heat because their particles are moving. The more movement, the more heat. Some of this heat is emitted as infrared (an EM wave). In a vacuum or space, all of it is transferred by radiation. An object hotter than its surroundings emits more IR than it absorbs (as it cools down). An objects colder than its surroundings absorbs more radiation than it emits (as it warms up). Put your hands in front of a fire or feel the heat from the sun and you’re feeling thermal radiation (IR).
What is conduction?
The process where vibrating particles transfer energy from their kinetic energy store to the kinetic stores of neighbouring particles i.e. heat makes particles vibrate. These particles make particles next to them move.
What does heat travel through when it comes to conduction?
Heat travels through and between touching objects (solids).
Why do metals conduct heat very fast?
Metals conduct heat very fast because the free electrons can easily move. Metals have a unique structure with lots of free electrons (they’re not bound to an atom).
When does convection occur?
Convection occurs when the more energetic particles move from the hotter region to the cooler region and transfer energy as they do so.
Is hot air less or more dense than cool air?
Hot air is less dense than cool air.
What are convection currents?
Hot air rises and cool air sinks down to replace it. These movements are called convection currents and often create a circular motion in a room.
Why is hot air less dense?
Hot air is less dense because it has more kinetic energy. All particles move. The more they move, the further apart they can get so hot air expands. This is how we get things turn from liquid to gas. The particles move so much they break away from the others. Hot air has more energy. Its particles move further apart and the density of the air decreases (there’re less particles per given area of space). As they cool, they get closer together and denser.
Why can’t convection happen in solids?
Because the particles can’t move (apart from vibrating which they do in conduction).
Give examples of convection.
Boiling water in a kettle & heat rising from a radiator or fire.
What’s a cavity wall? What happens if there’s no insulation in the cavity?
A cavity wall is when two walls have a gap in the middle. It can be filled with an insulating material or left as air. If there’s no insulation in the cavity, heat is trapped because air is a bad conductor.
