Chapter 6 - Thermal Physics

Question 1

How do we observe Brownian motion?

Answer 1

• 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.

Question 2

Pressure = ?

Answer 2

The force exerted per unit area of the surface.

Question 3

SAS of particles in a solid?

Answer 3

Slow, regular, close

Question 4

SAS of particles in a liquid?

Answer 4

Medium speed, touching but irregular arrangement and close spacing

Question 5

SAS of particles in a gas?

Answer 5

Fast, no arrangement, large spacing

Question 6

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

Answer 6

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

Question 7

Why is water more dense than ice?

Answer 7

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

Question 8

What energy increases when particles break free of their neighbours?

Answer 8

Their electrical potential energy (EPE).

Question 9

Describe electrical potential energy against separation graph?

Answer 9

• 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.

Question 10

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

Answer 10

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

Question 11

Latent heat of fusion = ?

Answer 11

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

Question 12

Latent heat of vaporisation = ?

Answer 12

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

Question 13

Evaporation = ?

Answer 13

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

Question 14

What is formed due to evaporation?

Answer 14

Vapour.

Question 15

Why does evaporation happen?

Answer 15

• 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

Question 16

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

Answer 16

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.

Question 17

What is the kinetic model?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

Define internal energy?

Answer 19

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

Question 20

Two ways to change internal energy?

Answer 20

Heat it or compress it (do work on it)

Question 21

Explain how thermometers work?

Answer 21

• 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

Question 22

Define thermal energy?

Answer 22

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

Question 23

Define thermal equilibrium?

Answer 23

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

Question 24

How does the Celsius scale work?

Answer 24

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

Question 25

How does the Kelvin scale work?

Answer 25

2 fixed points: - absolute zero (KE and EPE at minimum) - triple point of water (273.16K)

Question 26

Kelvin to celcius?

Answer 26

-273 degrees

Question 27

Celcius to kelvin?

Answer 27

+273 degrees

Question 28

Define thermodynamic scale?

Answer 28

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

Question 29

Define absolute zero?

Answer 29

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

Question 30

Define specific heat capacity?

Answer 30

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

Question 31

3 factors affecting the energy required to heat a material?

Answer 31

- Material - Mass of material - Desired temperature of material

Question 32

What is specific heat capacity measured in?

Answer 32

Represented by c Measured in Joules per kilogram per kelvin

Question 33

Energy require to heat a substance equation?

Answer 33

E = mcΔθ

Question 34

What does a low specific heat capacity mean?

Answer 34

It means it heats quickly.

Question 35

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

Answer 35

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

Question 36

Equipment for SHC experiment? (8)

Answer 36

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

Question 37

What are the problems with the SHC experiment?

Answer 37

- heating too fast can lead to uneven temperature through the material - the material will release heat as it heats up

Question 38

Define specific latent heat?

Answer 38

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'

Question 39

Method for SHC experiment? (5)

Answer 39

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