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UNIT 5 PHYSICS > C1 Physics > Flashcards

C1 Physics Flashcards

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1
Q

What are the four parts of a refrigerator?

A
  • Compressor
  • Condensor coils
  • Expansion device
  • Evaporator coils
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2
Q

What is the role of the compressor in a fridge?

A

Heats up to compress + condense coolant vapour into liquid

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3
Q

What is the role of condensor coils in a fridge?

A
  • Removes heat from coolant
  • transfers it to surroundings via conduction and radiation
  • The thin metal coils aid conduction, this condenses vapour into liquid
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4
Q

What is the role of the expansion device in a fridge?

A
  • Liquid coolant expands and becomes vapour, which decreases its temperature
  • Expansion is adiabatic
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5
Q

What is the role of evaporator coils in a fridge?

A
  • To remove heat energy from fridge by transferring it to coolant
  • Energy transferred causes coolant to evaporate and become vapour
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6
Q

How does a compressor affect a fridges efficiency?

A

It heats up when condensing vapour which wastes energy and reduces its efficiency

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7
Q

How do condensor coils affect a fridges efficiency?

A

Efficiency of cooling and condensing vapour depends on temp difference between coolant and surroundings. Not all heat can be removed from coolant and surroundings.

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8
Q

How does an expansion device affect a fridges efficiency?

A

Almost 100% efficient

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9
Q

How do evaporator coils affect a fridges efficiency?

A

Efficiency of cooling inside of fridge depends on how fast heat can be extracted from fridge

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10
Q

What do refrigerators and heat pumps do?

A

Devices that transfer heat energy from colder objects to hotter objects, by doing work.

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11
Q

What do heat engines do?

A

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

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12
Q

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?

A
  • 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
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13
Q

How do you convert celsius to kelvins?

A

+273

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14
Q

When is work done?

A
  • force moves an object + energy is transferred to object
  • the greater the force, the greater distance moved, more work is done
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15
Q

What is the equation for work done?

A

Work done = force x distance moved

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16
Q

Define power

A

Amount of energy supplied / work done per second

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17
Q

What is the equation for power?

A

Work done = power x time

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18
Q

Ideal Gas Equation:

When a gas is in a container, why does it exert pressure on walls?

A

Gas particles collide with eachother and walls

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19
Q

Ideal Gas Equation:

What does the amount of pressure by gas exerted on walls depend on?

A
  • volume
  • temp
  • number of molecules
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20
Q

What is the equation for the ideal gas equation?

A

Pressure x vol = number of moles x gas constant (8.31) x temp

P x v = n x r x t

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21
Q

What does the first law of thermodynamics state?

A

Energy cannot be created or destroyed, just transferred from one form into another

22
Q

What is the sum of all energy of particles in a system called?

A

Internal energy (U)

23
Q

What is the symbol for internal energy?

A

U

24
Q

What is the equation to measure change in internal energy?

A

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

25
Q

What happens as internal energy of a system inc?

A

As int energy of a system inc, temp inc

26
Q

What can the process of transferring energy between objects be called?

A

Isothermal or adiabatic

27
Q

Define isothermal process

A
  • 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
28
Q

What energy transfers are involved when heating boiling water and why does temp of water not increase?

A
  • 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
29
Q

Define adiabatic processes

A

No heat is transferred to or from the system e.g. using a spray can

30
Q

Aerosols (spray cans) become cold when sprayed, why?

A
  • 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
31
Q

What does the second law of thermodynamics state?

A

Heat energy never flows spontaneously (on its own) from a colder object to hotter object

32
Q

What do heat pumps and refrigerators do?

A

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
33
Q

What is the purpose of a fridge?

A

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
34
Q

What are the two equations for calculating efficiency?
For machines that are powered using heat energy such as heat engines

A

Efficiency = 1 - (Q out / Q in)

Efficiency = 1 - (Tc / Th)

35
Q

What are petrol engines?

A
  • 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
36
Q

What are the 5 stages to the operation of a petrol engine?

A

Intake
Compression
Ignition
Expansion
Exhaust

37
Q

What happens during intake stage in a petrol engine?

A

Fuel and air mixture is taken into piston

38
Q

What happens during compression stage in a petrol engine?

A

Piston compresses fuel and air mixture adiabatically
Volume of fuel + air mixture dec
Pressure inc

39
Q

What happens during ignition stage in a petrol engine?

A

Fuel + air mixture is ignited
Causes big inc in pressure and temp
No change in volume

40
Q

What happens during expansion stage in a petrol engine?

A

Gas expands adiabatically
Does work on piston to push it down
Volume of gas inc
Pressure dec

41
Q

What happens during exhaust stage in a petrol engine?

A

Piston is opened
This dec pressure with no change in volume
Gas leaves piston, which dec the volume

42
Q

When a solid goes straight to a gas, what is this called?

A

Sublimation

43
Q

Describe the features of the molecules in ice, water and steam

A

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

44
Q

Describe the energy of the molecules in solid ice, liquid water and gaseous steam

A
  • the higher temp of molecules, more energy molecules have
  • molecules in solid water have least ke
  • molecules in steam gas have most ke
45
Q

Describe what happens when you heat a block of ice starting from - 20 c to a gaseous steam

A

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

46
Q

What is the energy required to boil one kg of water called?

A

Specific latent heat of vapourisation

47
Q

What is the specific latent heat of vaporisation for water?

A

2.26 x10 6

48
Q

What is the equation for the specific latent heat of vapourisation?

A

Q (energy transferred) = change in mass of water that has been vapourised x specific latent heat of vaporisation for water

49
Q

What is the energy transferred to water when heating called?

A

Specific heat capacity

50
Q

When does an object being heated reach thermal equilibrium?

A
  • the energy flowing into object = energy flowing out of object
  • temp stops inc + reaches a maximum
51
Q

When an object is heated, its temp increases. What is the thermal capacity of an object?

A
  • amount of energy required to increase temp of the object by 1K

UNIT 5 PHYSICS (3 decks)

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