C1 Physics Flashcards
What are the four parts of a refrigerator?
- Compressor
- Condensor coils
- Expansion device
- Evaporator coils
What is the role of the compressor in a fridge?
Heats up to compress + condense coolant vapour into liquid
What is the role of condensor coils in a fridge?
- Removes heat from coolant
- transfers it to surroundings via conduction and radiation
- The thin metal coils aid conduction, this condenses vapour into liquid
What is the role of the expansion device in a fridge?
- Liquid coolant expands and becomes vapour, which decreases its temperature
- Expansion is adiabatic
What is the role of evaporator coils in a fridge?
- To remove heat energy from fridge by transferring it to coolant
- Energy transferred causes coolant to evaporate and become vapour
How does a compressor affect a fridges efficiency?
It heats up when condensing vapour which wastes energy and reduces its efficiency
How do condensor coils affect a fridges efficiency?
Efficiency of cooling and condensing vapour depends on temp difference between coolant and surroundings. Not all heat can be removed from coolant and surroundings.
How does an expansion device affect a fridges efficiency?
Almost 100% efficient
How do evaporator coils affect a fridges efficiency?
Efficiency of cooling inside of fridge depends on how fast heat can be extracted from fridge
What do refrigerators and heat pumps do?
Devices that transfer heat energy from colder objects to hotter objects, by doing work.
What do heat engines do?
Devices that use the spontaneous transfer of heat energy from hotter objects to colder objects and convert it into mechanical energy to do work.
Opposite of heat pumps and fridges
Heating a pan of boiling water is an example of an isothermal process ( temp stays constant).
What energy transfers are involved and why does temp of water stay constant and not increase?
- heat energy is transferred from fire to boiling water
- some water molecules vapourise from liquid into gas, which requires energy
- the energy supplied by fire is equal to the energy used to vapourise water molecules
- overall the internal energy of the water does not increase
How do you convert celsius to kelvins?
+273
When is work done?
- force moves an object + energy is transferred to object
- the greater the force, the greater distance moved, more work is done
What is the equation for work done?
Work done = force x distance moved
Define power
Amount of energy supplied / work done per second
What is the equation for power?
Work done = power x time
Ideal Gas Equation:
When a gas is in a container, why does it exert pressure on walls?
Gas particles collide with eachother and walls
Ideal Gas Equation:
What does the amount of pressure by gas exerted on walls depend on?
- volume
- temp
- number of molecules
What is the equation for the ideal gas equation?
Pressure x vol = number of moles x gas constant (8.31) x temp
P x v = n x r x t
What does the first law of thermodynamics state?
Energy cannot be created or destroyed, just transferred from one form into another
What is the sum of all energy of particles in a system called?
Internal energy (U)
What is the symbol for internal energy?
U
What is the equation to measure change in internal energy?
Change in internal energy = energy transferred to or from system by heating - energy transferred to or from system by doing work
(Change) U = Q - W
What happens as internal energy of a system inc?
As int energy of a system inc, temp inc
What can the process of transferring energy between objects be called?
Isothermal or adiabatic
Define isothermal process
- The temp of system remains constant e.g. heating a pan of boiling water
- As the energy that goes in is equal to energy that goes back out
What energy transfers are involved when heating boiling water and why does temp of water not increase?
- isothermal process
- heat energy is transferred from the fire to the boiling water
- some water molecules are vapourised from liquid into gas, which requires energy
- energy supplied by fire is equal to energy used to vapourise water molecules
- overall the int energy of liquid water doesnt change
- because (change) U = 0, Q - W becomes Q - W = 0 which rearranges to Q = W
Define adiabatic processes
No heat is transferred to or from the system e.g. using a spray can
Aerosols (spray cans) become cold when sprayed, why?
- adiabatic process
- when sprayed, the gas in can expands + does work by pushing away the surrounding air
- this requires energy, which comes from, the int energy of aerosol gas
- so aerosol becomes cold when it releases gas (as all the energy is taken out)
- this is adiabatic as no heat was transferred to or from can to make this process happen , Q (energy) = 0
- the only energy transferred was due to aerosol gas doing work on the surrounding air
- because Q = 0, (change) U = Q - W becomes (change) U - W
What does the second law of thermodynamics state?
Heat energy never flows spontaneously (on its own) from a colder object to hotter object
What do heat pumps and refrigerators do?
Devices that transfer heat energy from colder objects to hotter objects
- the 2nd law of thermodynamics tell us this wont happen so these devices must do work to make this happen
What is the purpose of a fridge?
Remove heat from inside of a fridge by transferring it to the air surrounding fridge
- this is done by compression and expansion of a coolant which is circulated around the fridge
What are the two equations for calculating efficiency?
For machines that are powered using heat energy such as heat engines
Efficiency = 1 - (Q out / Q in)
Efficiency = 1 - (Tc / Th)
What are petrol engines?
- examples of heat engines
- use heat released by combustion of a fuel to power a device
- there are 5 stages to the operation of a petrol engine
What are the 5 stages to the operation of a petrol engine?
Intake
Compression
Ignition
Expansion
Exhaust
What happens during intake stage in a petrol engine?
Fuel and air mixture is taken into piston
What happens during compression stage in a petrol engine?
Piston compresses fuel and air mixture adiabatically
Volume of fuel + air mixture dec
Pressure inc
What happens during ignition stage in a petrol engine?
Fuel + air mixture is ignited
Causes big inc in pressure and temp
No change in volume
What happens during expansion stage in a petrol engine?
Gas expands adiabatically
Does work on piston to push it down
Volume of gas inc
Pressure dec
What happens during exhaust stage in a petrol engine?
Piston is opened
This dec pressure with no change in volume
Gas leaves piston, which dec the volume
When a solid goes straight to a gas, what is this called?
Sublimation
Describe the features of the molecules in ice, water and steam
ICE
- close
- vibrate in a fixed position
- strong IMF bw molecules
WATER
- closer
- move by sliding past eachother
- IMF bw molecules are weaker than ice but stronger than steam
STEAM
- far apart
- able to move freely
- almost no IMF bw molecules
Describe the energy of the molecules in solid ice, liquid water and gaseous steam
- the higher temp of molecules, more energy molecules have
- molecules in solid water have least ke
- molecules in steam gas have most ke
Describe what happens when you heat a block of ice starting from - 20 c to a gaseous steam
Solid ice
- molecules held together by strong IMF
- as temp increases
- molecules gaining energy + vibrating more
Melting
- energy of molecules stays constant
- as energy transferred to ice is used to break IMF
- and turn solid ice to liquid water
Liquid water
- IMF forces are weaker
- molecules able to slide past one another
- as temp rises
- molecules are gaining ke + moving faster
Boiling
- energy of molecules stay constant
- as energy transferred to water is used to break IMF
- and turn liquid water into gaseous steam
Gaseous steam
- IMF are weakest
- molecules able to move freely
- as temp increases
- molecules gain ke + move faster
What is the energy required to boil one kg of water called?
Specific latent heat of vapourisation
What is the specific latent heat of vaporisation for water?
2.26 x10 6
What is the equation for the specific latent heat of vapourisation?
Q (energy transferred) = change in mass of water that has been vapourised x specific latent heat of vaporisation for water
What is the energy transferred to water when heating called?
Specific heat capacity
When does an object being heated reach thermal equilibrium?
- the energy flowing into object = energy flowing out of object
- temp stops inc + reaches a maximum
When an object is heated, its temp increases. What is the thermal capacity of an object?
- amount of energy required to increase temp of the object by 1K
