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A2 Physics > Chapter 6 - Thermal Physics > Flashcards

Chapter 6 - Thermal Physics Flashcards

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1
Q

How do we observe Brownian motion?

A
  • look at smoke through a microscope, see smoke grains move jerkily and erratically.
  • result of smaller O2 and N particles knocking them. Due to erratic motion of smoke, it shows that air molecules must too be MOVING and have HAPHAZARD motion.
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2
Q

Pressure = ?

A

The force exerted per unit area of the surface.

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3
Q

SAS of particles in a solid?

A

Slow, regular, close

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4
Q

SAS of particles in a liquid?

A

Medium speed, touching but irregular arrangement and close spacing

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5
Q

SAS of particles in a gas?

A

Fast, no arrangement, large spacing

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6
Q

Describe change of state as heat is added to a solid.

A

1) increase in temp of solid
2) no increase briefly due to energy being used to break solid bonds
3) increase in temp of liquid
4) no increase for longer time due to energy being used to break liquid bonds (more to break than solid to liquid so time is longer)
5) increase in temp of gas

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7
Q

Why is water more dense than ice?

A

The arrangement of water is more compacted than ice, since the regular arrangement of particles in ice creates large gaps between particles.

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8
Q

What energy increases when particles break free of their neighbours?

A

Their electrical potential energy (EPE).

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9
Q

Describe electrical potential energy against separation graph?

A
  • at low separation, EPE is large negative.
  • as it increases, separation does too but at EPE proportional to -1/r
  • EPE reaches 0 when the particles are completely separated.
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10
Q

What 4 things happen when a substance (eg. Water) is melting/ boiling (flat part of graph)?

A
  • energy is input
  • temperature doesn’t change
  • molecules break bonds between each other
  • EPE increases
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11
Q

Latent heat of fusion = ?

A

The energy which must be supplied to cause a substance to melt at a constant temperature.

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12
Q

Latent heat of vaporisation = ?

A

The energy which must be supplied to cause a substance to boil at a constant temperature.

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13
Q

Evaporation = ?

A

The process by which a liquid becomes a gas at a temperature below its boiling point.

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14
Q

What is formed due to evaporation?

A

Vapour.

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15
Q

Why does evaporation happen?

A
  • in a liquid particles move about
  • some move fast enough to break away from the liquid completely
  • some return by chance
  • but the result is a net outflow of molecules so eventually a liquid will evaporate completely
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16
Q

Why does the temperature of the liquid fall when it evaporates?

A

Evaporation occurs due to the particles with the highest KE escaping the liquid. This leads to a lower average KE. Since KE is directly proportion to temperature, a fall in average KE leads to a fall in temperature.

17
Q

What is the kinetic model?

A
  • matter is made of tiny particles
  • they move about
  • their important characteristics are MOTION, ORDERING and SPACING of atoms
18
Q

Why doesn’t water all boil away instantly at 100 degrees Celsius?

A

Because it takes time for energy to build up enough to break all the bonds.

19
Q

Define internal energy?

A

The internal energy of a system is the sum of the random distribution of kinetic and potential energies of its atoms or molecules.

20
Q

Two ways to change internal energy?

A

Heat it or compress it (do work on it)

21
Q

Explain how thermometers work?

A
  • energy is transferred from a hotter object to a cooler one (from substance to thermometer)
  • at equal temperatures, two objects will not transfer energy to each other
  • when the thermometer is equal temperature to the substance, the reading on it will be the temperature of the thermometer
22
Q

Define thermal energy?

A

Energy transferred from on object to another because of a temperature difference.

23
Q

Define thermal equilibrium?

A

A condition when two or more objects in contact have the same temperature so that there is no net flow of energy between them.

24
Q

How does the Celsius scale work?

A

Takes boiling and melting point of water, divides range into 100 equal intervals, each one is one degree.

25
Q

How does the Kelvin scale work?

A

2 fixed points:

  • absolute zero (KE and EPE at minimum)
  • triple point of water (273.16K)
26
Q

Kelvin to celcius?

A

-273 degrees

27
Q

Celcius to kelvin?

A

+273 degrees

28
Q

Define thermodynamic scale?

A

A temperature scale where temperature is measured in Kelvin(K).

29
Q

Define absolute zero?

A

The temperature at which a system has minimum internal energy, equivalent to 0 kelvin.

30
Q

Define specific heat capacity?

A

The specific heat capacity of a substance is the energy required per unit mass of the substance to raise the temperature by 1Kelvin.

31
Q

3 factors affecting the energy required to heat a material?

A
  • Material
  • Mass of material
  • Desired temperature of material
32
Q

What is specific heat capacity measured in?

A

Represented by c

Measured in Joules per kilogram per kelvin

33
Q

Energy require to heat a substance equation?

A

E = mcΔθ

34
Q

What does a low specific heat capacity mean?

A

It means it heats quickly.

35
Q

How does the specific heat capacity of water affect its uses?

A

Water has a very high SHC.
This means it heats and cools very slowly.
This makes it ideal for cooling systems and central heating.

36
Q

Equipment for SHC experiment? (8)

A 
Power supply
Temperature probe
Computer
Metal cylinder (to be heated)
12V electrical heater
Data logger
Ammeter
Voltmeter
37
Q

What are the problems with the SHC experiment?

A
  • heating too fast can lead to uneven temperature through the material
  • the material will release heat as it heats up
38
Q

Define specific latent heat?

A

The specific latent heat of a substance is the energy required per kilogram of the substance to change its state without any change in temperature.

Specific means ‘per unit mass’

39
Q

Method for SHC experiment? (5)

A

1) connect up circuit.
2) use electrical heater to supply energy to cylinder.
3) voltmeter and ammeter determine energy being supplied, this is recorded by data logger.
4) temperature probe records temperature of block and sends information to data logger.
5) information is sent to computer where it is displayed

A2 Physics (25 decks)

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