heat transfer Flashcards
What is absolute zero
The temperature which cannot become lower(-273)
What is absolute zero in degrees Celsius and kelvin?
Absolute zero= 0K ,-273C
What is Kelvin
It is the same as degrees Celsius but starts at absolute zero (-273)
What is freezing point of water in degrees Celsius and kelvin?
0 degrees Celsius, 273 degrees Kelvin
What is boiling point of water in degrees Celsius and kelvin?
100 degrees Celsius, 373 degrees Kelvin
what is the formula to turn degrees Celsius into kelvin
C + 273 = K
what is the formula to turn degrees Kelvin into Celsius
K - 273 = C
What is 50 degrees C into K
323K
What is - 50 degrees C into K
223K
What is 50 degrees K into C
-223C
What is 200 degrees C into K
473K
What is 123 degrees K into C
-150C
What is the definition of
the thermal store of energy
Energy stored in an objects thermal store
What is the definition of
temperature
The average kinetic energy per particle in an object
Why are there no negative numbers on the Kelvin scale
It starts at absolute zero so temperature cannot get any colder meaning there are no negatives
When you touch a cold surface, does cold travel from the surface to your hand, or does heat travel from your hand to the surface? Explain.
heat travels from your hand to the surface because heat always flows form a higher temperature to a lower temperature and your hand is warmer than the cold surface.
Where does thermally stored energy (heat) transfer from and to?
heat always transfers to a colder object until thermal equilibrium is reached
What is the definition of conduction
Conduction is the transfer of heat through direct contact between particles in a substance.
Explain what happens in conduction
In materials, such as metals, heat energy is conducted when vibrating particles pass on their energy to neighbouring particles through collisions. This process occurs in solids.
In conduction - do all materials conduct at the same rate and why?
No, lots of factors affect rate of conduction. Metals conduct quicker because they have lots of free electrons. A thicker material slows heat transfer because heat has to travel a longer distance. A larger temperature difference between two objects affects the rate of heat transfer. A larger contact area allows more heat to be transferred.
What is the definition of convection?
Definition: Convection is the transfer of heat through the movement of fluids (liquids or gases).
Explain what happens in convection
In fluids, warmer regions become less dense and rise, while cooler regions become denser and sink. This creates a cycle of circulating currents that transfer heat.
Convection occurs in liquids and gases.
What is the definition of radiation?
Radiation is the transfer of heat through electromagnetic waves that do not require a medium (solid, liquid, or gas) for propagation (to travel/move)
Explain what happens in radiation
Heat from the source travels in the form of electromagnetic waves, and it can travel through a vacuum. This process can occur in a vacuum or through transparent materials.
Heat from the source travels in the form of electromagnetic waves, and it can travel through a vacuum. This process can occur in a vacuum or through transparent materials.
Why is a lightbulb hot to touch
Thermal conduction occurs and heat conducts from the lightbulb to your hand
Why can you feel heat when you hold your hand over a lightbulb?
Convection currents in the air transfers heat to your hand as the particles in the current rise up and down.
Why can you feel warmth if you hold your hand 20cm to the side of a lightbulb?
Radiation heat transfer occurs and electromagnetic waves from the lightbulb hit your hand.
How does heat get from the sun to the earth
radiation
what type of electromagnetic radiation is radiation heat transfer
Infrared
True or false: Radiation travels in staight lines
True it travels as infrared waves in a uniform medium so it is in straight lines.
True or False: Radiation can travel through a vacuum
True, does not need particles to move through
Radiation requires particles to travel
False, it comes in the form of electromagnetic waves so it doesnt need straight lines
Radiation travels at the speed of light
True, this is true for all electromagnetic waves unless it is in materials because it is slightly decreased due to refraction
Are matt (dull) black surfaces good emitters of radiation and why
They emit energy most quickly - they are good radiators
Are shiny silvery surfaces good emitters of radiation and why
They are poor radiators of heat energy
Why are kettles often silver
to reduce radiation heat transfer so the water can remain hot
What colour should we paint our radiators
black
Why don’t we paint our radiators black
They mainly heat by convection
