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physics a - level > Further Mechanics and Thermal Physics (3): Thermal Physics > Flashcards

Further Mechanics and Thermal Physics (3): Thermal Physics Flashcards

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1
Q

What are the two scenarios in which energy transfer takes place between two objects?

A
  1. If one object exerts a force/does work on another
  2. If one object is hotter than the other -> energy transfer takes place by heating due to the temperature difference between the two objects
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2
Q

What are the 3 ways that energy is transferred by heating?

A
  • Conduction
  • Convection
  • Radiation
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3
Q

Definition of internal energy of an object?

A

The sum of the random distribution of the kinetic and potential energies of its molecules

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4
Q

2 ways internal energy is increased?

A
  1. Energy transferred by heating the object
  2. Work done on the object
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5
Q

2 reasons why the internal energy of an object is a constant?

A
  1. There is no energy transfer to the object -> no heating or work done
  2. Energy transfer by work done and heating balance each other out
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6
Q

Why does the internal energy of a lamp filament increase when a lamp is switched on?

A

Work is done by by the electricity supply pushing electrons through the filament

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7
Q

At a lamps operating temperature what is true about the internal energy of the filament? Why?

A

Internal energy is a constant

-> This is because the work done by electricity to push electrons through the filament is balanced by the energy transfer by heating to the surroundings and light radiated from the filament

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8
Q

State the first law of thermodynamics

A

When work is done on or by an object and/or energy is transferred by heating:

“the change of internal energy of the object = the total energy transfer due to work done and heating”

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9
Q

Describe the movement of molecules/atoms in a solid?

A

They vibrate about fixed positions

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10
Q

What happens to the molecules/atoms in a solid when it is heated?

A

The kinetic energies of the molecules/atoms are raised

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11
Q

What happens to the molecules/atoms in a solid when it melts?

A

This is when the temperatures are high enough so the molecules/atoms have enough kinetic energy to break free from each other causing the substance to lose its shape

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12
Q

When a solid melts what happens to the internal energy of the substance?

A

Increases

  • Increased temperature -> Increased kinetic energy
  • Molecules break free from one another -> Increased potential energy
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13
Q

Describe the movement of molecules/atoms in a liquid?

A

The molecules/atoms move about at random but in contact with one another

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14
Q

What happens to the molecules/atoms in a liquid when it is heated?

A

The particles/atoms gain kinetic energy -> internal energy increases

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15
Q

What happens to the molecules/atoms in a liquid when it turns into a gas?

A

This is when the temperatures are high enough so the molecules/atoms have enough kinetic energy to break free completely from each other an move away from each other

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16
Q

When a liquid -> gas what happens to the internal energy of the substance?

A

Increases

  • Increased temperature -> Increased kinetic energy
  • Molecules break free completely from one another -> Increased potential energy
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17
Q

Describe the movement of molecules/atoms in a gas?

A

Move about randomly but much further apart on average comparative to in a liquid state

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18
Q

What happens to the molecules/atoms in a gas when they are heated?

A

Increases the kinetic energies of the molecules/atoms therefore the internal energy of the substance

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19
Q

A gas has maximum…?

A

Potential energy

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20
Q

Definition of temperature

A

A measure of the degree of how hot a substance is

21
Q

Temperaturewise, is an object has more internal energy it will be…?

A

Hotter

22
Q

Temperaturewise, is an object has less internal energy it will be…?

A

Cooler

23
Q

If you place your hand of temperature X degrees into a water bath of that same temperature, what happens?

A

Nothing - there is no transfer of energy by heating

24
Q

Any two objects that have the same temperature are said to be at…?

A

thermal equilibrium with each other

25
Q

Definition of triple point of water

A

The temperature, in kelvin, at which ice, water and water vapour co-exist in thermodynamic equilibrium

26
Q

What is the temperature at the triple point of water?

A

273.16K

27
Q

At absolute zero what is the internal energy of an ideal gas?

A

0

28
Q

What 3 factors does the temperature rise of an object depend on?

A
  1. Mass of the object
  2. Amount of energy supplied to it
  3. Substance or substances from which the object is made
29
Q

Definition of specific heat capacity, c?

A

The energy needed to raise the temperature of a unit mass of the substance by 1K without a change in state

30
Q

What is the equation for the energy needed to raise the energy, Q of a substance?

A

Q = mc(delta)T

31
Q

Describe how the inversion tube experiment can be used to determine the specific heat capacity of a substance?

A

In this experiment GPE is converted into internal energy when the object (of a specific material) hits the bottom of a tube. In this experiment the object is tiny (lead - can be any material) spheres. The tube is then inverted each time the spheres hit the bottom of the tube.

-> The temperature of the object is measured initially and then again after a particular number of inversions

Calculation:
1. Let m represent mass of the object
2. For tube length, L, the loss of GPE from each inversion = mgL
3. For n inversions, loss of GPE = mgLn
4. The gain of internal energy of the object = mc(delta)T
5. Assuming all GPE lost is transferred to the internal energy of the object

mc(delta)T = mgLn
c = gLn/ (delta)T

32
Q

Describe how you can use an electrical method to determine the specific heat capacity of a block of material

A
  1. Drill 2 holes into an insulated block of material
  2. Determine mass, m, of the insulated material
  3. A 12V electrical heater is inserted into one of the holes and used to supply a measured amount of electrical energy to the material block
  4. A thermometer is inserted into the second hole and is used to measure (delta)T -> Final T - Initial T

Electrical energy supplied:
= Heater current x heater pd x heating time

Assuming no heat lost to the surroundings:
mc(delta)T = IVt
c = IVt/m(delta)T

NB: By using a small amount of water/oil in the hole with the thermometer you will improve the thermal contact between the thermometer and the metal

33
Q

Describe the method used to determine the specific heat capacity of a liquid?

A
  1. A known mass of liquid is placed in a calorimeter of known mass an known specific heat capacity
  2. A 12V electrical heater is placed into the heater an used to heat it directly
  3. A thermometer is inserted into the liquid and used to measure the temperature rise

Electrical energy supplied:
= Heater current x heater pd x heating time

Energy needed to heat the liquid:
Q = m(of liquid)c(of liquid)(delta)T

Energy needed to heat the calorimeter:
Q = m(of calorimeter)c(cal)(delta)T

Assuming no heat losses to the surroundings:
IVt = m(l)c(l)(delta)T + m(cal)c(cal)(delta)T

34
Q

What should you always do before taking a temperature reading of a liquid?

A

Stir it

35
Q

What is an electric shower?

A

When water passes steadily through copper coils heated by an electrical heater

36
Q

Is the water in an electrical shower hotter or colder at the outlet?

A

Hotter

37
Q

How do solar heating panels work?

A

The solar panels absorb energy in the form of light radiation which is transferred to the thermal energy store of the panels. This is transferred by heating to a liquid that flows through the panel.

38
Q

What is the equation for the energy gained per second by heating of the liquid in a solar panel?

A

mc (delta)T/t

39
Q

Density of states from least to most?

A

gas < liquid < solid

  • As more particles in a given volume
40
Q

What is the name given to the energy needed to melt a solid at its melting point?

A

Latent heat of fusion

41
Q

What is the name given to the energy needed to vaporise a liquid at its boiling point?

A

Latent heat of vaporisation

42
Q

At the latent heat of fusion and vaporisation why does the temperature of the substance not increase?

A

As the thermal energy is being used to break the bonds between the atoms and is not transferred to their kinetic energy stores

43
Q

What is released when a liquid solidifies or a vapour condenses?

A

Latent heat -> the energy required to break the bonds in the first place

NB - some of this latent heat is used to keep the temperature at the melting point until all of the liquid has solidified

44
Q

What happens as a liquid solidifies?

A

The molecules move slowly enough for the force bonds between them to form again and lock the molecules in place

45
Q

Define sublimation?

A

When a solid turns into a gas (vaporises) directly when heated

46
Q

Definition of specific latent heat of fusion

A

The energy needed to change the state of a unit mass of the substance from solid to liquid without a change in temperature

47
Q

Definition of specific latent heat of vaporisation

A

The energy needed to change the state of a unit mass of the substance from liquid to gas/vapour without a change in temperature

48
Q

What is the equation for the energy needed to change the state of mass , m, of a substance from solid to liquid/liquid to vapour without a change in temperature?

A

Q = ml

where:
l - specific latent heat of fusion/vaporisation

49
Q

Describe the graph of temperature against internal energy?

A
  1. Initially, substance is a solid. As it is heated the internal energy increases proportionally to the temperature until the melting point.
  2. At the melting point the graph flattens as there is no temperature change as the substance changes state
  3. The graph returns to same gradient as before as liquid is heated an gains internal energy
  4. Then flattens again during boiling
  5. The continues to rise as before

physics a - level (24 decks)

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