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13 Physics > Thermal physics > Flashcards

Thermal physics Flashcards

To revise thermal physics

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1
Q

Define internal energy

A

Sum of the individual potential and kinetic energies of all molecules within the body

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2
Q

State the first law of thermodynamics

A

The change of internal energy of the object is equal to the total energy transfer due to work done and heating

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3
Q

Define specific heat capacity

A

The energy required to change the temperature of 1kg of the substance by 1K without changing state

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4
Q

Describe the experiment to measure the specific heat capacity of a metal

A

Metal block of known mass in an insulated container. Electrical heater inserted into a hole in the metal, thermometer into another.
Measure the temperature change over a given time

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5
Q

Which measurements are used to measure specific heat capacity of a metal, and how?

A 
Heater's current (I)
Heater's pd (V)
Time of heating (t)
Temperature change (ΔT)
mcΔT=IVt (rearrange for c)
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6
Q

State Boyle’s law

A

When a fixed mass of gas is reduced in volume by a compressing piston, the pressure inside the piston increases

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7
Q

Explain why Boyle’s law is true

A 
Gas particles all in motion
Pressure exists from surface collisions exerting a force
Volume decreases
Collisions occur more frequently
Pressure increases
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8
Q

State Charles’ law

A

For a fixed mass of an ideal gas at constant pressure, its volume is directly proportional to its absolute temperature

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9
Q

State the pressure law

A

For a fixed mass of an ideal gas at constant volume, its pressure is directly proportional to its absolute temperature

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10
Q

Define Avogadro constant

A

The number of atoms in exactly 12g of carbon-12

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11
Q

Define molar mass

A

The mass of 1 mol of the substance

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12
Q

What are the five assumptions that are made for the kinetic theory equation?

A 
Molecules are point molecules
No attractive forces between molecules
Molecules move in continual random motion
All collisions are elastic
Time of collisions is negligible
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13
Q

Define molar heat capacity

A

The energy required to change 1 mol of gas by 1K

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14
Q

Define heat capacity

A

The energy required by an entire object to change temperature by 1K

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15
Q

How is work done on a gas calculated from a pressure against volume graph?

A

Area under the graph

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16
Q

Explain what is meant by specific latent heat of fusion (2)

A

The energy required to change one kg of an object from liquid to solid without changing temperature

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17
Q

Water is pumped througha heater in a hot tub, why is the temperature rise greater when the pump works at a higher speed? (2)

A

The pump is doing work on the water. Work can raise the temperature of the body

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18
Q

Use the kinetic theory of gases to explain why the pressure inside a football increases when the temperature of the air inside it rises. Assuming volume remains constant (3)

A

Molecules have a greater rms velocity. Number of collisions between molecules and inside surface of ball increases per second. pressure = F/A and F = rate of change of momentum

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19
Q

What is the equation for Work Done in a Piston with a set mass of gas in?

A

A: W = p ΔV W = Work Done p = Pressure ΔV = Change in Volume

20
Q

What is the Second Law of Thermodynamics?

A

It is not possible to convert heat continuously into work, without at the same time, transferring some heat from a warm body into a cold body. : the total entropy of a system can never decrease over time (temperature of an object always wants to be in equilibrium with surroundings).

21
Q

What is the equation for Force?

A

F = p x A F = Force p = Pressure A = Cross-Sectional Area

22
Q

What is the equation for internal energy for constant pressure processes?

A

ΔU = ΔQ – pΔV ΔU = Change in Internal Energy ΔQ = Change in amount of heat supplied to the system p = Pressure ΔV = Change in Volume

23
Q

What does the p-V graph look like for constant pressure (isobaric process)?

A

Horizontal line

24
Q

What does the area below a p-V graph show?

A

Work Done

25
Q

What are the rules for a cycle process?

A

1) For a complete cycle, ΔU = 0 (No change in internal energy)
2) the net work done = area enclosed by the cycle

26
Q

How do you change from Celsius into Kelvin?

A

Celsius Temperature + 273

27
Q

What is specific latent heat?

A

The amount of thermal energy required to change the state of 1 kg of a substance at constant temperature

28
Q

What are the three equations for an ideal gas?

A

pV = NkT pV = nRT pV = (1/3)Nmc²

29
Q

What are the equations for average kinetic energy?

A

KE = (1/2)m c² = (3/2)kT = (3/2)(RT/Nₐ)

30
Q

What is the main property of a gas at absolute zero?

A

It has minimum internal energy

31
Q

Define temperature

A

a measure of the average kinetic energy of the particles in a system

32
Q

Define heat

A

the flow of thermal energy

33
Q

Define thermal equilibrium

A

when two objects are at the same temperature so there is no flow of heat.

34
Q

What causes pressure?

A

The collisions between gas particles and the inside walls of the container

35
Q

What are the properties of an ideal gas

A
  1. Molecules move with random motion, 2. Molecules obey Newton’s laws, 2. Molecules have same average kinetic energy, 3. There are no attractive forces between molecules, 4. Collisions between molecules are elastic, 5. Molecules are point masses (have zero volume), 6. Time taken between collisions is much greater than during collisions.
36
Q

Describe Brownian motion

A

particles moving randomly due to collisions with many other small, fast particles.

37
Q

State the third law of thermodynamics

A

the entropy of an ideal substance will be zero at absolute zero (0K).

38
Q

What is Avogadro’s constant?

A

The number of atoms in exactly 12g of carbon-12 (6.02x1023)

39
Q

What is the specific latent heat of fusion?

A

The energy needed to change the state a substance from solid to liquid without a change of temperature.

40
Q

What is the specific latent heat of vaporisation?

A

The energy needed to change the state a substance from liquid to gas without a change of temperature.

41
Q

Define empirical

A

Based on observation or experience rather than theory or pure fact.

42
Q

What is meant by the term elastic collisions?

A

Both KE and momentum are conserved and total E is constant before and after the collision

43
Q

Define absolute scale

A

Measured in K starting at absolute zero

44
Q

Particles exert pressure on the wall of a container because…

A

Molecules have momentum
Momentum change at wall
Momentum change at wall leads to force

45
Q

Why is average velocity in a container zero?

A

Velocity is a vector
random direction
velocities cancel

46
Q

Sublimation

A

a chemical process where a solid becomes a gas without going through a liquid stage

47
Q

What is the difference between heat and temperature?

A

Heat is the flow of thermal energy as it flows from a high temperature to a low whereas temperature is a measure of the kinetic energies of the particles in a selected substance.

13 Physics (21 decks)

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