Chapter - 11 (Thermal Energy Transfer) Flashcards
What are Good thermal conductors?
Solids (Ex - metal pan or ceramic cup)
Tiles
Stones
What are bad thermal conductors (insulators)?
- Wollen blanket
- Layers of paper & carpet
Why do we feel the tile is cold?
- Heat is transferred away from the foot making the tile feel colder
why do we not feel cold on the rug?
- Insulators
- Heat is not transferred away from the foot
Which state does conduction happen in?
solids
When does conduction occur?
Two solids of different temperatures come in contact with one another, thermal energy is transferred from the hotter objects to the cooler objects.
Why are metals the best conductors?
They have free electrons
What are the 2 mechanisms that conduction happens in?
- Atomic vibrations
- Free electrons collisions
What happens when a substance is heated?
- Ions move around and vibrate
- they bump into each other
- collision transfer thermal energy until thermal equilibrium is reached
Why does conduction not happen easily in fluids?
- Particles are close together but slide past each other
- gas particles are too far apart
In which states does convection happen in?
Liquids and gases
What happens when liquid or gas is heated?
- Molecules push each other apart making the liquid or has expand.
- hot liquids n gas becomes less dense
- hot liquid/gas rises
- hot liquid/gas eventually cools down and sinks again.
- the convection current then repeats
What happens when a liquid or gas is cooled?
- molecules move together making the liquid/gas contract.
- This makes hot liquid/gas more dense than surroundings
How can you demonstrate convection currents?
Take a beaker and add potassium permanganate
How does the hotness affect the thermal radiation?
The hotter the object is, more thermal radiation it emits.
What is thermal radiation a part of?
Electromagnetic spectrum called infrared
What is thermal radiation a way?
The only way in which heat can travel in vacuum
What happens when an object absorbs thermal energy?
- It emits more thermal radiation
What happens when the temp of the body increases?
Absorbs radiation faster than it emits radiation
What happens when an object is absorbing at the same rate it is emitting radiation?
- Constant temp
- Thermal equilibrium
When will the object cool down?
If the rate at which an object receives energy is less than the rate at which it transfers energy away.
When will the object heat up?
If the rate at which an object transfers energy is away is less than the rate at which it receives energy
- always moves to thermal equilibrium
What are the factors that’s effect the thermal radiation emitted?
- Surface colour (Black = more radiation)
- Texture (Shiny surfaces = more radiation)
- surface area (greater surface area = more area for radiation)
What would happen if the Earth had no atmopshere?
Temp on the earth’s surface will drop to - 180°C at night (same as moon’s temp surface)
Why does the temp of the surface on earth drop in absence of Earth’s atmosphere?
The surface might emit all radiation from sun into space.
What factors is the temp on earth affect by?
Balance between incoming radiation and radiation emitted
How does the earth emit thermal radiation?
With a slightly longer wavelength than the thermal radiation it receives.
How do gases on Earth absorb and emit thermal radiation?
Water vapour, methane, and CO 2 absorb and reflect back longer - wavelength infrared radiation and prevent it from escaping into space.
What do the gases in atmosphere do in simpler terms?
Absorb radiation and emit back to the surface
What factors do the earth’s temp depend on?
Rate at which light and infrared radiation from the sun are:
- Reflected back into space
- Absorbed by the atmosphere or by earth’s surfaces
- emitted from the earth’s surface and from earth’s surface
What contributes to the greenhouse effect?
Rate of absorption and emission of radiation on earth
What happens when the sun’s thermal radiation reaches the earth’s atmosphere?
- Some radiation is reflected back to space
- any radiation not reflected is absorbed and re-radiated by greenhouse gases
In which state
