Thermal Physics

Question 1

What is absolute zero

Answer 1

Lowest theretically possible temperature which is zero kelvin or -273 degrees

Question 2

What is usual room temperature and atmospheric pressure at sea level

Answer 2

Room temperature : 20 degrees, 293 Kelvin
Atmospheric pressure (at sea level) : 101 kPa

Question 3

What is boyles law

Answer 3

Pressure of gas is inversely proportional to volume
At a fixed mass of gas and at a constant temperature

Question 4

For boyles law, draw a graph of pressure against volume. Draw two graphs with one v having a higher temperature

Answer 4

Question 5

State Charles law

Answer 5

A fixed mass of gas at a constant pressure, has volume of gas directly proportional to temperature

Question 6

Draw a graph to represent Charles’ law and draw two graphs with one having a higher pressure

Answer 6

Question 7

State the pressure law (Gay-Lussacs law)

Answer 7

A fixed mass of gas at a constant volume, pressure is proportional to temperature

Question 8

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Question 9

Derive Boltzmann equation from ideal gas equation

Answer 9

Question 10

Define pressure and state equation linked

Answer 10

Pressure is normal force per unit surface area over which the force acts
Pressure = force / area

Question 11

State use of equation that links work done, pressure and volume

Answer 11

Energy needed/ released is area under graph

Question 12

In molecular kinetic theory, state what happens when molecules hits wall of container

Answer 12

Question 13

What are the 5 ideal gas laws in molecular kinetic theory

Answer 13

1. Total volume of each molecule is negligible compared to the total volume of the gas
2. The intermolecular forces between molecules are negligible
3. Time between collisions with container walls and other molecules is much greater than the duration of collisions
4. Collisions between container walls and other molecules are considered elastic
5. There are a large number of molecules who’s motion is random

Question 14

What is Brownian motion

Answer 14

When particles are inserted into something, particles are moving randomly
E.g if you have dust particles suspended in a gas, gas molecules collide with dust particles and gas particles start moving randoml

Question 15

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Question 17

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Question 18

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Question 19

What does average velocity equal to

Answer 19

Crms
Start with square, then mean, then square root

Question 20

How do you calculate total kinetic energy of a gas

Answer 20

Number of molecules x average kinetic energy of a molecule

Question 21

What is internal energy

Answer 21

Question 22

Define specific heat capacity

Answer 22

Specific heat capacity is energy needed to raise temperature of 1kg of a substance by 1 Kelvin

Question 23

Define thermal equilbrium

Answer 23

Two objects are in thermal equilbrium if there is no net energy transfer between them when they are placed in contact

Question 24

When two objects off current temperatures are placed into contact, how do they reach thermal equilbrium

Answer 24

Question 25

How else can you write Q=mc x delta t, get rid of Q

Answer 25

P is power not pressure

Question 26

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Question 27

Define specific latent heat of fusion

Answer 27

Energy required to change 1kg of a substance from a solid to a liquid at its melting point

Question 28

Define specific latent heat of vaporization

Answer 28

Energy required to change 1kg of a substance from a liquid to a gas at its boiling point

Question 29

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Question 30

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Question 31

Define the Avogadro constant

Answer 31

Number of atoms in 12 grams of carbon-12

Question 32

State units of mean square speed

Answer 32

m^2 s^-2

Question 33

Outline what is meant by an ideal gas

Answer 33

Question 34

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Question 35

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Question 36

Answer 36

Must use 3RT/2Na as they contain all constants apart from temperature Temperature = 320 Kelvin

Question 37

Answer 37

B

Question 38

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Question 39

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A

Question 40

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Question 43

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Question 44

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Question 45

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Question 46

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Question 47

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Question 48

Answer 48

I = p/v gives 19.6 A Current required for 4.5 kW would exceed fuse rating

Question 49

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Question 50

Answer 50

Kinetic energy is exchanged in molecular collisions Until average kinetic energy of all molecules is the same

Question 51

Answer 51

Curve A below original Curve B above original

Question 52

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Question 53

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Question 54

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Question 55

An assumption is that molecules are in a state of random motion. What is meant by random motion

Answer 55

Molecules have a range of speeds They have no preferred direction of movement

Question 56

Skip calculation part, as long as you get equation needed correct

Answer 56

Question 57

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Question 58

Just do biii) using the table

Answer 58

Temperature is proportional to kinetic energy At 0 Kelvin, kinetic energy would be zero As there would be a straight line through the origin

Question 59

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Question 60

Assumptions made when estimating time it takes for water to turn into ice

Answer 60

Constant rate of heat loss Ice remains at zero degrees

Question 61

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Question 62

Answer 62

Ice requires energy to melt Stays at zero degrees for longer and cools for longer

Question 63

Two cylinders require exact amount of energy to raise the temperature but one has molecules with greater mass. Explain why they require exact amount of energy

Answer 63

As they have same number of molecules and same increase in average kinetic energy

Question 64

Explain why average velocity of gas molecules in a container is zero

Answer 64

Velocity is a vector Random velocity means no preferred direction of movement Velocities cancel out

Question 65

Gas undergoes a change from A to B. Volume at A is 0.7 x 10^-3 m^3 and pressure at A is 10^5 Pa and temperature at A is 27 degrees. Volume at B is 0.5 x 10^-3 m^3 and pressure at A is 10^5 Pa. Calculate change in temperature from A to B

Answer 65

Use VA/TA = VB/TB However you got it wrong Because you need to say MINUS 86, remember final temp is lower so must be a minus

Question 66

Compare work done on gas during change of A to B with that of B to C

Answer 66