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Physics > Thermal Physics > Flashcards

Thermal Physics Flashcards

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1
Q

What is the triple point of a substance

A

One specific temperature and pressure where the three phases of matter can exist in thermal equilbrium

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2
Q

Define Thermal Equilibrium

A

No net transfer of thermal energy between the phases

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3
Q

What happens when objects are in thermal equilibrium

A

There is no net flow of thermal energy between them

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4
Q

What happens when Object A is warmer than Object B

A

Net flow of thermal energy is from Object A to Object B

Object A gets warmer
Object B gets colder

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5
Q

What is the 0th Law of Thermodynamics

A

If 2 objects are each in thermal equilibrium with a third, then all three are in thermal equilibrium with each other

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6
Q

What forms the basis of temperature

A

0th Law of Thermodynamics

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7
Q

What is needed in order to measure temperature

A

A scale is needed with 2 fixed points at defined temperatures

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8
Q

Describe the Celsius Scale

A

Freezing + Boiling Points as the 2 fixed points
There are 100 increments between 0 and 100 degrees celsius

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9
Q

Why is the Celsius scale not perfect

A

Freezing and Boiling Points vary at different atmospheric temperatures

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10
Q

What is the Absolute Temperature Scale also known as

A

Thermodynamic Temperature Scale

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11
Q

Describe the Absolute Temperature Scale

A

Uses triple point of pure water and absolute zero

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12
Q

What must any object at 100 degrees celsius be

A

In thermal equilibrium with boiling water

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13
Q

SI Base Unit for Temperature

A

Kelvin (K)

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14
Q

Kelvin Formula

A

Degrees Celsius + 273

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15
Q

What is Kelvin always

A

Positive

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16
Q

Describe Electrostatic Forces for different phases of matter

A

Solid - Strong
Gas - Negligible

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17
Q

What does the Kinetic Model describe

A

How all substances are made up of atoms or molecules - which are all arranged differently depending on the phases of the substance

18
Q

Density in Water

A

Less dense in solid than in liquid

One of the rare substances to do this

19
Q

What is Brownian Motion

A

The haphazard movement of particles of a substance caused by the transfer of momentum through elastic collisions with particles of a surrounding medium

20
Q

How Brownian Motion observed

A

Robert Brown looked through a microscope and recorded his observations of the random arrangement of fine pollen grains floating on water

21
Q

How did Einstein explain Brownian Motion

A

In terms of collisions between the pollen grains and millions of tiny water molecules

These collisions were elastic and resulted in a transfer of momentum from water molecules to the pollen grains which made them move in haphazard ways

22
Q

How can Brownian Motion be observed

A

Using a smoke cell - particles of smoke are large enough to be seen under a microscope
They move in a random way and are surrounded by air molecules
Air molecules are constantly striking the smoke particles
Air molecules are in random motion
Mean KE of Smoke = Mean KE of air molecules
Air molecules of 500 ms^-1 - Smoke molecules are more massive and move much more slowly

23
Q

Density for most substances between phases of matter

A

Most dense in solids
Lease dense in gases

24
Q

Define Internal Energy

A

The sum of randomly distributed kinetic and potential energies of atoms or molecules within the substance

25
Q

Why can the Potential Energy of a Substance never be 0

A

At 0K there is no kinetic energy but there’s electrostatic potential energy stored between the particles

26
Q

What happens when a substance reaches its melting or boiling point, while it is changing phase

A

The energy transferred to the substance does not increase its temperature
EPE of the substance increases as the electrical forces between the atoms or molecules change

27
Q

When does KE of atoms or molecules increase during phase changes

A

It doesn’t - potential energy changes

28
Q

EPE for different phases

A

Gas = 0J
Liquid = Negative = energy must be supplied to break atomic/molecular bonds
Solid = Large negative

29
Q

When is EPE lowest and highest

A

Lowest in Solids
Highest in Gas (0J)

30
Q

Electrostatic Forces in Gas and Solid

A

Gas = Negligible
Solid = Large

31
Q

What is specific heat capacity of a substance

A

Energy required per unit mass to change the temperature by 1 K

32
Q

Equation for specific heat capacity

A

E = mass x specific heat capacity x change in temperature

33
Q

Experiment for specific heat capacity

A

Use an electric heater

Insulate surroundings to minimise energy loss

Stir liquid carefully to make sure there is uniform temperature throughout

34
Q

Specific heat capacity equation with an electric heater

A

IVt / (mass x change in temperature)

35
Q

What is specific latent heat of a substance

A

Energy required to change the phase per unit mass while at constant temperature

36
Q

Equation for specific latent heat

A

L = E / m

E is energy supplied to change the phase of mass of the substance

37
Q

What is the specific latent heat of fusion

A

Energy supplied to change from solid to liquid phase

38
Q

What is the specific latent heat of vapourisation

A

Energy supplied to change the substance from liquid to gas

39
Q

What graph can be used to give a more accurate value for specific heat capacity

A

Temperature of the substance against time

40
Q

Temperature time graph equations

A

E / change in T = mc x (change in temperature / change in time)

Gradient is change in temperature / change in time

Constant power supplied = E / change in time

Power = mc x gradient

c = P / (m x gradient)

41
Q

What is the method of mixtures

A

Another way to determine specific heat capacity

Known masses of two substances at different temperatures are mixed together - recording final temperature at thermal equilibrium allows specific heat capacity of one of the substances to be determined if the specific heat capacity of the other is known

Physics (19 decks)

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