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IGCSE Physics > Thermal Physics > Flashcards

Thermal Physics Flashcards

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1
Q

What is the kinetic theory?

A

Each material is made of tiny particles that are in continuous motion and the motion increases as they gain the average kinetic energy which is proportional to the temperature of the matter

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2
Q

What is the arrangement of particles in solids?

A

Close together, regular pattern and equal distances between molecules

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3
Q

What is the arrangement of particles in liquids?

A

Close together random equal distances between the molecules

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4
Q

What is the arrangement of particles in gases?

A

Far apart random

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5
Q

What is the movement of solid particles?

A

Vibrate about a fixed position

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6
Q

What is the movement of liquid particles?

A

Vibrate but may change position with each other

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7
Q

What is the movement of gas particles?

A

Move quickly in any direction randomly

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8
Q

What is the forces between solid particles?

A

Held together by strong forces of attraction

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9
Q

What is the forces between liquid particles?

A

Attract each other but their attraction can’t hold them in a fixed positions

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10
Q

What are the forces between gas particles?

A

Virtually free of any attraction

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11
Q

Why do solids have a fixed shape and cannot flow?

A

Their particles cannot move from place to place

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12
Q

Why can’t solids be compressed or squashed?

A

The particles are close together and have no space to move into

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13
Q

Why can’t liquids be compressed?

A

Because the particles are close together

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14
Q

What is the kinetic model of gas?

A

When the particles of a gas collide with the walls of the container they exert a force. The pressure of a gas is the sum of all these forces divided by the area. The force is larger if the particles are moving faster or if there are more particles colliding within the walls. Thus the higher the temperature and the greater the number of collisions and the harder the collisions the larger the pressure

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15
Q

What is the kinetic model of gas in terms of momentum?

A

Collisions with walls causes rebounding that causes change in momentum. Since the force is the rate of change of momentum, there is a force exerted on the walls of the container therefore there is a pressure

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16
Q

What is evidence for moving particles?

A

Brownian motion

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17
Q

How do particles travel?

A

In zig zag pattern

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18
Q

Why do particles travel zig-zag?

A

Air molecules are moving faster and randomly so they bombard the smoke particles randomly from all directions causing the smoke particles to move randomly.

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19
Q

State the equation needed to convert Celsius into kelvin

A

C + 273

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20
Q

For the liquid in glass thermometer, the thermometric property is the volume of the liquid. Explain.

A

When a liquid is heated, it expands. The expansion is related to the temperature. This volume can be calibrated with the temperature.

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21
Q

For the bimetallic strip, the thermometric property is the length of solid. Explain

A

It consists of two strips of different metals- iron and brass. When the temperature rises each metal expands a different amount which causes the bar to bend. The greater expansion of brass compared that of iron makes the brass curve round on the outside of the iron. This causes a pointer to move up and down indicating a temperature change.

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22
Q

For the thermistor, its thermometric property is its electrical resistance. Explain

A

Electronic components that suffer a resistance change with change of temperature. For a thermistor the measurement of a specific temperature will result in a specific resistance across the thermistor.

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23
Q

For the thermocouple, its thermometric property is the electromotive force. Explain.

A

It consists of two wires, each of a different metal. Both ends form junctions. One of those junctions is kept at a constant temperature- 0 C and as the temperature of the other junction changes a small voltage is generated. The voltage is measured by a millivoltmeter and this can be calibrated to give a reading of the temperature.

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24
Q

Explain how you can calibrate a thermometer.

A

Place a thermometer in a mixture of ice water and mark the O degree mark. Then place the thermometer in boiling water and mark the thermometer. 100 EQUALLY spaced divisions can be placed between to represent 1 C marks

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25
Q

Define Sensitivity

A

The change in property per unit degree

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26
Q

What increases the sensitivity of a thermometer?

A

The narrower the tube

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27
Q

What is the most sensitive substance?

A

thermocouple them alcohol then mercury

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28
Q

Define Range

A

It is the difference between the maximum and minimum temperatures that the thermometer can read.

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29
Q

How can you increase the range?

A

Increasing the diameter of the capillary and decreasing the volume of the bulb

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30
Q

Which substances have the biggest range?

A

Thermocouple, alcohol freezes at -114 C whereas mercury at -39 C, and alcohol boils at 78 C whereas mercury boils at 357 C

31
Q

Define linearity

A

When the liquid expands by the same amount for every degree Celsius rise in temperature

32
Q

Which substance is NOT linear?

A

Thermocouple

33
Q

Which substances are linear?

A

Mercury and alcohol

34
Q

Define responsiveness

A

How long it takes for the thermometer to react to a change in temperature

35
Q

How can you increase responsiveness?

A

Making the glass bulb thinner or making the bulb smaller

36
Q

Which substance is the most responsive and why?

A

Thermocouple because the probe is too small and it has small heat capacity

37
Q

How does heat flow?

A

From where it is hot to where it is not until thermal equilibrium is reached

38
Q

What happens when a matter is heated?

A

The volume will increase slightly

39
Q

Explain why a material expands when heated

A

When any matter is heated its particles speed up so their vibrations take up more space so they expand slightly in all directions

40
Q

How do you increase thermal expansion?

A

The length is increased
The material has a higher expansion
Temperature difference

41
Q

What are bimetallic strips used for?

A

Thermostats

42
Q

State the relationship between pressure and temperature and explain.

A

Increasing the temperature increases the pressure. Molecules move faster and there is an increase in collisions and the average force per collision increases. Since the area of the flask does not change and the force increases pressure increases.

43
Q

State the relationship between volume and temperature and explain.

A

Increasing the volume will increase the temperature . This is because the average velocity of the gas particles increase which increases rate of collisions and the average force.

44
Q

State the relationship between pressure and volume and explain.

A

Volume is inversely proportional to pressure. A decrease in volume increases the number of gas particles. This results in an increase in the number of gas particles close to the cylinder walls and therefore an increase in the number of collisions with the wall. Increased force per area therefore greater pressure.

45
Q

State Boyle’s Law

A

p1 * V1 = p2 * v2

46
Q

How does conduction occur in metals?

A

Free electrons move at high speed at hot end and have high KE. Collide with slow moving electrons and KE is transferred during collisions.

47
Q

How does conduction occur in non metals?

A

Molecules vibrate slowly at hot end and have more KE and attractive forces between molecules cause them to vibrate too. KE passes from hot to cold. This process is slow and that is why non- metals are good insulators of heat.

48
Q

What is radiation?

A

The transfer of heat by electromagnetic waves

49
Q

What affects the rate of absorption/emitter of radiation?

A

Dull and rough black surfaces are good absorbers and emitters of radiation.
Shiny and smooth white surfaces are poor absorbers and poor emitters of radiation

50
Q

Everyday examples of radiation?

A

Cooling fins at the back of fridge are painted black
Solar panels are painted black
Glass wall in thermos flask are silvered

51
Q

What is conduction?

A

The transfer of heat from two objects in contact and there is no difference between them.

52
Q

What is convection?

A

The transfer of heat by movement of heated liquids or gases

53
Q

How does convection take place?

A

Heated gas expands and the volume increases but the mass is UNCHANGED it becomes less dense rises upwards and the cold gas sinks and a convection current in set up. Heat is transferred from hot region to cold region.

54
Q

Why is there a vacuum in a thermos flask?

A

As to prevent convection from taking place

55
Q

How does thermal energy rate transfer increase?

A

Temp difference across the ends increased
The cross-sectional area is increases
Length of bar is reduced
Using better conductor

56
Q

State insulating materials used in the house to reduce amount of thermal energy lost

A
  1. Plastic foam around hot water tank
  2. Glass/wool insulations in the loft
  3. Wall cavity is filled with wool/plastic foam
  4. Double glazed windows- two sheets of glass with air in between
57
Q

Explain how the thermos flask is made to avoid heat loss

A

Vacuum- conduction and convection prevented
Foam support- Traps air which is a poor conductor of heat
Plastic stopper- poor conductor of heat, convection and evaporation can only occur when it is removed

58
Q

What is evaporation?

A

The process of converting liquid into vapours

59
Q

How does evaporation happen?

A

The energetic molecules at the surface leave the surface because they are less bonded so the average energy decreases and therefore the temperature decreases

60
Q

Characteristics of evaporation

A

Happen at any temperature

Happens at the liquid surface only

61
Q

What is boiling?

A

Process of converting liquid into vapours at boiling point

62
Q

How does boiling happen?

A

As a result of increasing the temperature of liquid the molecules start moving faster and gain enough energy to break intermolecular bonds and escape from liquid. Average energy stays THE SAME and so does the temperature.

63
Q

Characteristics of boiling

A

Happens only at boiling point of liquid

Happens anywhere in liquid

64
Q

How to increase the rate of evaporation?

A

Increase temperature
Increase SA
Reduce humidity
Increase wind

65
Q

Define specific heat capacity

A

The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1kg of the substance by 1 C

66
Q

Give the equation for heat capacity

A

C * m

the specific heat times the mass

67
Q

Give the equation for the specific heat capacity

A

E = mass(kg) * specific heat capacity * change in temperature

E=mcΔt

68
Q

What is fusion?

A

Substance changes from solid to a liquid

69
Q

What happens when a substance changes its state?

A

THE TEMPERATURE REMAINS CONSTANT

70
Q

Define specific latent heat of fusion

A

The energy that is needed to change the state of a 1kg from solid to liquid at its melting point

71
Q

Define specific latent heat of vaporization

A

The energy that is needed to change the state of a 1kg from liquid to vapour at its boiling point

72
Q

What is the equation for specific latent heat?

A

E= mass * specific latent heat

E=mL

73
Q

When we have two equations to do in one question what do we do first?

A

E= mL then E= m*c *Δt

IGCSE Physics (12 decks)

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