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Physics Unit 1 > Thermal Physics > Flashcards

Thermal Physics Flashcards

1
Q

Potential Energy

A

The energy the particles of a substance have due to stretching of the bonds between them.

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2
Q

Kinetic Energy

A

The energy the particles of a substance have due to their motion.

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3
Q

Thermal Energy

A

The sum of the potential and kinetic energy of the particles in a substance.

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4
Q

Temperature

A

Measure of average kinetic energy of the particles in a substance.

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5
Q

Absolute Zero

A

Coldest temperature that can theoretically exist. Particles have zero kinetic energy. 0 K or -273(.15) °C

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6
Q

Thermal Equilibrium

A

A state in which two objects are at the same temperature; the net flow of energy between them is zero.

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7
Q

Specific Heat Capacity

A

The energy change required to change the temperature of 1 kg of a substance by 1 K.

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8
Q

Water high specific heat capacity

A

Amongst solids and liquids water has a notably high specific heat capacity. This means that large changes in energy are needed for small changes in temperature.

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9
Q

Latent Heat

A

The energy change required to change 1 kg of a substance from one state to another. The energy absorbed/released by a substance as it changes states.

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10
Q

Conduction

A

Transfer of energy through matter by passing energy from particle to particle by collisions, dominant energy transfer method in solids. Very weak in gases, very strong in metals.

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11
Q

Convection

A

Transfer of energy through matter by particles carrying energy, dominant energy transfer method in fluids.

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12
Q

Natural Convection

A

Convection is where the particle movement occurs naturally due to density/pressure gradients in the fluid e.g. hot air rising

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13
Q

Forced Covection

A

Convection where the particle movement occurs due to an artificial driver e.g. fan-driven computer cooling

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14
Q

Radiation

A

Transfer of energy by emitted electromagnetic radiation, dominant energy transfer method in a vacuum.

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15
Q

Factors Promoting Radiation

A

Rough (high surface area), black surfaces are the best at absorbing and emitting radiation.

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16
Q

Factors Minimising Radiation

A

Smooth (low surface area), white/silver surfaces are the worst at absorbing and emitting radiation.

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17
Q

Minimising Conduction/Convection

A

Insulation typically traps pockets of air. As a gas, the air is a very poor conductor and since it is trapped it cannot convect. E.g. jumper, ceiling batts, fur.

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18
Q

Conservation of Energy

A

The total energy in a system cannot change, it can be transferred between objects and transformed into different forms.

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19
Q

Change of State (melting, boiling)

A

At a specific temperature, the substance does not gain kinetic energy, so temperature remains constant, it only gains potential energy as the bonds between particles are stretched and then broken as it changes states.

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20
Q

Change of state (freezing, condensing)

A

At a specific temperature, the substance does not lose kinetic energy, so temperature remains constant, it only loses potential energy as new bonds form between particles as it changes states.

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21
Q

Thermal Expansion

A

As matter gains potential energy the particles stretch further apart, causing the substance to expand.

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22
Q

Thermal Contraction

A

As matter loses potential energy the particles relax closer together, causing the substance to contract.

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23
Q

Latent Heat of Fusion

A

Solid and Liquid

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24
Q

Latent Heat of Vaporisation

A

Liquid and Gas

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25
Q

Energy Cooling In Cars

A

A petrol vehicle only converts 12-30% of the chemical energy stored in its fuel into kinetic energy in the wheels. The rest is converted into other forms of energy – mostly heat. Excess heat must be removed to prevent damage to the engine.

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26
Q

Car Cooling System

A

A pump: this pushes coolant around the engine.
A thermostat: this releases coolant into the radiator once it reaches a high temperature.
A radiator: this is a set of tubes surrounded by thin pieces of metal called radiator fins. Heat from the coolant is transferred to the fins, which then transfer it to the air moving past them.
A fan: this pulls air through the radiator as required to increase the rate of cooling.

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27
Q

Heat Pump (movement of energy from cold place to hot place)

A
  1. A compressor pressurises a gas called refrigerant, driving up its temperature.
  2. The refrigerant travels through a set of tubes called a condenser, where it releases heat to its surroundings and condenses into a liquid.
  3. The refrigerant is depressurised by an expansion valve, which causes it to cool down.
  4. The now-cool refrigerant travels through an evaporator, absorbing heat from its surroundings and turning into a gas as it does so. It then re-enters the compressor and the cycle repeats.
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28
Q

Refrigerator (heat pump)

A

the condenser is on the back, surrounded by radiator fins (similar to a car radiator)
the evaporator is inside the refrigerator, where it absorbs heat from the refrigerator’s contents
Refrigerators are usually equipped with adjustable thermostats, which turn off the compressor at a set temperature.

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29
Q

Air Conditioning

A

Refrigerate air conditioners also rely on heat pumps:
the condenser is outside, where fins and a fan assist with heat transfer to the air (similar to a car radiator)
the evaporator is inside, where it absorbs heat from the air
The cooled air is blown into the room by another fan.

30
Q

Evaporative Air Conditioning

A

Evaporative air conditioners cool a room by using the cooling effect of evaporating water.
air is forced through a wet filter pad
heat from the air is absorbed as the water in the pad evaporates
the cooled air is forced into the room by a fan

31
Q

Positioning of Rooms

A

Rooms used most during day in north end to use winter sun
Bedrooms placed in south where they stay cool during summer

32
Q

Insulation

A

Double Glazed Windows
Double Brick Walls
Fibreglass Insulation

33
Q

Double Glazed Windows

A

Window made up of two glass panels with an air pocket in between - since air is a poor conductor of heat, this slows down the flow of heat into the house

34
Q

Double Brick Walls

A

Made of two brick panels with air pocket in between

35
Q

Fibreglass insulation

A

As an insulator, fiberglass works to trap air and slow the transfer of heat.

36
Q

Shade

A

Trees and other sources of shade prevent sunlight into a house
Deciduous trees lose leaves in colder months

37
Q

Thermal Mass

A

A materials ability to absorb, store and release heat

38
Q

High Thermal Mass

A

Materials with high thermal mass (brick, concrete, stone) are helpful in summer because they absorb lots of heat before slowly releasing it into the house
In winter they absorb heat during day and release it at night, keeping house warm

39
Q

Builders often insulate parts of homes with material that consists of a thin shiny sheet of reinforced aluminium foil. How does this material reduce heat transfer?

A

Aluminium foil reduces heat transfer because aluminium reflects 95% of the heat that hits its surface. This blocks heat transfer. It blocks the flow of radiation which makes it useful in preventing heat loss.

40
Q

Swimmers often notice that when they start to swim in a still body of water after a hot, sunny day the surface water is warm but the deeper water is cold. Explain why this happens.

A

The water at the top of the pool is heated by the suns radiation and hotter water is less dense so it’ll stay at the surface, whereas colder water stays at the surface. This is convection because convection only occurs in liquids. There’s a convection current when warm fluids rise up and cool fluids fall.

41
Q

Efficiency

A

Efficiency is the ratio between the useful work done by a machine and the total energy expended to do that work. Its expressed as a percentage according to the following formula:

42
Q

When the temperature of a substance rises

A

The kinetic energy of the particles within that substance increases

43
Q

Solids

A

Attractive forces hold particles in fixed positions, repulsive forces prevent lattice from collapsing
Vibrate around equilibrium positions, given solids fixed volume and shape

44
Q

Liquids

A

Particles have more KE, inter-particle forces weaker
Particles move past one another, variable shape
Fixed volume

45
Q

Gases

A

Greater KE than liquid/solid
Move rapid in random straight lines until they collide with other particles
Collisions elastic due to high speed and low attractive forces
Variable shape and volume

46
Q

Zeroth Law of Thermodynamics

A

“If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other”

47
Q

When particles move further apart or change state,

A

, the energy used to overcome the inter-particle forces is converted into potential energy

48
Q

If the heating causes an increase in temperature,

A

it gains kinetic energy and if it causes expansion or a change of state, it gains potential energy

49
Q

When mechanical work is done on a system,

A

it increases the internal energy of the system and when mechanical work is done by a system, its internal energy decreases

50
Q

First Law of Thermodynamics

A

“When energy passes into or out of a system as work or heat, the systems internal energy changes in accord with the law of conservation of energy”

51
Q

A systems change in internal energy (U) is equal to the heat added to the system (Q) plus the work done on the system (W)

A

Change in Thermal energy = Heat + Work

52
Q

If the mass of water in the pot is doubled, it will take twice as long to achieve a given temperature increase

A

Thermal energy proportional to mass

53
Q

The longer the water is heated, the more its temperature will increase

A

Thermal energy proportional to change in temp

54
Q

Liquid Water High Specific Heat Capacity

A

Liquid water has a particularly high heat capacity meaning that it takes a large amount of energy to change its temperature (useful in motor cooling)

55
Q

Metal Low Heat Capacity

A

Metals with low heat capacities but high melting points like iron are useful for cookware as they are excellent conductors of heat and their low heat capacity minimises the heat that is “wasted” in heating up the cookware rather than the food inside

56
Q

Temperature remains ___ when state changes

A

Constant (it doesnt change)

57
Q

Whenever a substance goes from solid to liquid or liquid to gas it must gain ____

A

Potential Energy

58
Q

When water is heated it gains ____ causing a rise in temp (temp to increase)

A

Thermal energy

59
Q

Different substances have diff latent heats due to differences in the

A

arrangements of particles and the strength of their interparticle forces

60
Q

Conduction

A

No net movement of particles
Mostly in solids
Occurs by collisions or movement of free electrons
Transfers heat slowly due to low vibrational velocity of particles

61
Q

Thermal Conductivity

A

Conductors are substances that transfer heat by collisions and free electrons
Insulators have no free electrons
Solids best conductors, particles closer together
Gas good insulator, low density limit number of colissions

62
Q

Rate of conduction increases with

A

Increasing thermal conductivity/ temp difference
Decreasing thickness/surface area

63
Q

Convection (movement of hot particles of fluid)

A

Mass movement of particles over a distance
When heated, Particles gain KE so they move rapidly and further apart
Decrease density of hotter portion of fluid
Less dense, hotter fluid rise up and denser cool fluid fall down

64
Q

Convection Current

A

The upward movement of hot fluid and downward movement of cold fluid is called a convection current

65
Q

Natural Convection

A

When a fluid rises as its heated
Land and sea breezes, air above land more vulnerable to temp changes than air above ocean
Water high (C) keeps temp constant

66
Q

Sea Breeze and Land During Day

A

Air above land heats up and rises
This air replaced by cooler, denser air from above ocean (sea breeze) at night reverse process occurs

67
Q

Sea Breeze and Land During Night

A

Warm air above ocean rises and is replaced by cool dense air from above land (land breeze)

68
Q

Forced Convection

A

Occurs when fluid heated and blown by fan
Example: fan forced oven, ducted heating

69
Q

Radiation (electromagnetic radiation)

A

Electromagnetic radiation consists of electromagnetic waves that travel at the speed of light

70
Q

Rate of Radiant Depends on

A

Surface area, increase with rate of radiant
Surface colour and texture: rough matte black surfaces absorb more than white shiny smooth surfaces

Physics Unit 1 (3 decks)

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