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BTEC Science > Unit 5 - Physics > Flashcards

Unit 5 - Physics Flashcards

Revision for Unit 5 test

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1
Q

How do you convert Celsius to Kelvin?

A

Add 273.15

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2
Q

How do you convert Kelvin to Celsius?

A

Subtract 273.15

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3
Q

How do you calculate work done using distance and force?

A

Force multiplied by distance

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4
Q

How do you calculate pressure using force and area?

A

Force divided by area

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5
Q

How do you calculate efficiency?

A

1 - (Qout ÷ Qin)

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6
Q

What is an adiabatic process?

A

A process that involves no transfer of heat - internal energy is converted into work and vice versa.

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7
Q

What is an isothermal process?

A

A process that involves no change in temperature - all heat added is converted into work.

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8
Q

What is the unit for efficiency?

A

There is no unit for it

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9
Q

What is a heat engine?

A

Device that converts thermal energy into useful work

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10
Q

How quickly do isothermal processes happen?

A

Very slowly

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11
Q

What stays constant in an isothermal process?

A

Temperature of gas

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12
Q

What does the work in an isothermal process?

A

Engine transfer

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13
Q

Is insulation needed in an isothermal process?

A

No because heat needs to flow

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14
Q

How quickly do adiabatic processes happen?

A

Rapidly

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15
Q

What stays constant in an adiabatic process?

A

Engine heat

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16
Q

What does the work in an adiabatic process?

A

Temperature of gas

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17
Q

Is insulation needed in an adiabatic process?

A

Yes, it has to be completely thermally insulated

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18
Q

What is the first law of thermodynamics in an equation?

A

Q = △U+W (Change in internal energy + Work Done)

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19
Q

What is the first law of thermodynamics in words?

A

The heat energy supplied to a system is equal to the increase in the internal energy of the system plus the work done by the system on its surroundings

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20
Q

What is the second law of thermodynamics in words?

A

Heat always flows from a hot source to a cold sink unless we do work on a system. In a natural process, the entropy (randomness) of a system always increases. A natural process can never be fully reversed.

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21
Q

What is an idealised engine cycle?

A

An idealised engine more efficient than any that could actually be built. It describes the limits of what is possible.

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22
Q

Are you doing well?

A

Yes

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23
Q

What does entropy mean?

A

How much disorder there is in a system

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24
Q

Second law of physics in words?

A

In a natural thermodynamic process, the sum of entropies of the interacting systems increases.

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25
Q

Second law of physics equation

A

Qₕ - Q꜀ = W

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26
Q

Explain how a heat pump can keep us at a regular temperature at all times in the year

A

Heat pumps use energy to transfer heat from a cold to a hot reservoir. Heat pumps use a refrigerant/compressor, vapour and condenser so the refrigerant vapour condensed to liquid is releasing energy to the environment. This system is reversible, gives heat in winter and cools in the summer.

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27
Q

What is the unit for CoP?

A

There is no unit, it’s a ratio

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28
Q

How can you lower the cost of the CoP?

A

By keeping the temperature difference small. For example, using very large condenser coils and evaporators in a heat pump.

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29
Q

What is CoP?

A

CoP is the ratio of the energy transferred for heating the input energy. (For heat pumps and heat engines)

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30
Q

Can CoP be higher than 1?

A

Yes

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31
Q

What is the equation for CoP?

A

Thot / (Thot - Tcold)

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32
Q

What is thermal (heat) capacity?

A

The energy required to raise the temperature of an object by 1℃. The unit is JK⁻¹

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33
Q

What is specific heat capacity?

A

The energy required to raise the temperature of 1kg of a material by 1℃. The unit is JKg⁻¹K⁻¹.

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34
Q

What is the specific heat capacity formula?

A

Q=mc△T

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35
Q

What are the four steps in a heat pump cycle?

A

Compressor, condenser, expansion valve, evaporator

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36
Q

What steps are isothermal and which are adiabatic?

A

Condenser and evaporator are isothermal. Compressor and expansion valve are adiabatic

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37
Q

How does a heat pump differ from a heat engine?

A

Heat pumps draw in heat from a cold area and transfer to a warmer area. Heat pump is the reverse of a heat engine

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38
Q

What is it called when solid turns to liquid?

A

Melting

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39
Q

What is it called when liquid turns to gas?

A

Evaporation/boiling

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40
Q

What is called when a liquid turns to a solid?

A

Freezing

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41
Q

What is it called when a gas turns to a solid?

A

Deposition

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42
Q

What is it called when a solid turns to a gas?

A

Sublimation

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43
Q

What is called when a gas turns to a liquid?

A

Condensing

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44
Q

What is latent heat?

A

Latent heat is the energy needed to change the state of a substance without changing its temperature

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45
Q

What are the three forms of latent heat?

A

Fusion, vaporisation, and condensation

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46
Q

What is the specific latent heat equation?

A

Heat energy / Mass

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47
Q

Explain what happens to particles as they are gaining latent heat

A

The energy increases which is used to break bonds between particles.

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48
Q

Explain why sweating cools us down, by using the idea of latent heat

A

Sweating contains water with a high specific heat capacity. Energy from our skin is transferred to the water, and is transferred to break bonds. As particles evaporate, they transfer energy away from the skin, cooling it down.

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49
Q

When a bike pump is used to inflate a tyre, it gets hot. What happens to the internal energy of a gas if it is rapidly compressed, and why?

A

When work is done on the gas by the surrounding to compress it, the overall internal energy will increase.

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50
Q

When a gas in a deodorant can is sprayed, it rapidly cools. What happens to the internal energy of a gas if it is rapidly expanded, and why?

A

The gas does work in order to spread out and push air out of the way. Thus it transfers internal energy to do work, and this comprises only kinetic energy, this decreases and so does the temperature.

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51
Q

Fridges can transfer heat from a cold area to a warmer area. Explain why this does not violate the second law of thermodynamics

A

This is not a natrual process because it is powered by electricity

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52
Q

What is the purpose of the evaporator coils?

A

They transfer heat from the warmer internal fridge environment to the colder coolant. This adds latent heat to the refrigerant, evaporating it.

53
Q

Explain why a good refrigerant needs to have a low boiling point (around -30℃)

A

It needs to be able to reach boiling point when absorbing small amounts of energy from warmer (but still cold) food an air in the fridge, so that it can start absorbing latent heat quickly

54
Q

Why does a good refrigerant need to have a low specific heat capacity?

A

This helps a rapid increase in temperature for small additions of overall energy

55
Q

Why does a good refrigerant need to have a high latent heat of vaporisation?

A

At boiling point the refrigerant needs to absorb a large amount of latent energy transferred from the food, in order for it to carry heat away from the internal of the fridge to keep things cool

56
Q

What is plastic deformation?

A

A permanent deformation

57
Q

What causes plastic deformation?

A

Excessive force

58
Q

What is elastic deformation?

A

When a deformed object goes back to its original shape once force has stopped being applied

59
Q

What is length in terms of Hooke’s law?

A

Original length before force is added

60
Q

What is extension in terms of Hooke’s law?

A

The difference between the original length and the new length once force is added

61
Q

Why do Hooke’s law graphs always have a positive correlation?

A

Extension is directly proportional to force

62
Q

How do you convert mass into a force in spring constant questions?

A

Mass x 9.81

63
Q

What is meant by a plastic material?

A

A material that cannot return to its original shape after being stretched

64
Q

How can the energy stored in a spring be obtained from a Hooke’s Law Graph?

A

The area under the curve shows the elastic potential energy in the spring

65
Q

Why does the temperature of a gas increase when it is compressed?

A

When we compress a gas, work is being done on the gas. Work done creates energy and this means there’s more energy in the gas which causes the temperature to increase

66
Q

What is tensile stress?

A

Tensile stress describes the force an object experiences per unit area when being stretched

67
Q

What is the tensile stress equation?

A

Force divided by area

68
Q

What are the units for tensile stress?

A

Nm⁻² (Newtons per metre)

69
Q

What is strain?

A

Strain is the ratio of extension to original length

70
Q

What is the equation for strain?

A

Change in length / Original length (△x / L )

71
Q

What is young’s modulus?

A

Young’s modulus, E, is the ratio of stress to strain

72
Q

What does young’s modulus show?

A

How much an object will extend when a force is applied

73
Q

What is the equation for Young Modulus

A

E = Stress / Strain

74
Q

Is stress directly proportional to strain for a spring?

A

Yes, provided the elastic limit hasn’t been reached

75
Q

How is Young’s modulus obtained?

A

From the gradient of a stress/strain graph

76
Q

How do you calculate gradient on a graph?

A

Rise ÷ Run

77
Q

What is density?

A

Mass per unit volume

78
Q

What is the equation for density?

A

Mass ÷ Volume

79
Q

What are the two units for density?

A

kg/m³ g/cm³

80
Q

What are the units of Young Modulus?

A

N/m²

81
Q

Why are materials brittle?

A

Materials are brittle because they absorb relatively little energy before they fracture

82
Q

Can ductile metals be stretched into a wire?

A

Yes because they can deform under tensile stress

83
Q

Why can malleable materials be hammered or rolled into a sheet?

A

Because they can deform under compressive stress

84
Q

What is creep?

A

Creep is a gradual extension and deformation under a constant load

85
Q

What are examples of creep?

A

Old leap pipes sagging over time, heavy trolley wheel flattening, steel screws becoming loosing

86
Q

What is fatigue caused by?

A

Fatigue is caused by the continual loading and unloading of a material

87
Q

What is an example of fatigue?

A

Bending a paper clip and continuously bending the paper clip until it breaks

88
Q

Do rubber and elastic bands show elastic hysteresis?

A

Yes

89
Q

What does the centre of a hysteresis loop represent?

A

The area in the centre of the hysteresis loop is equal to the energy lost by the material

90
Q

Why does temperature increase during elastic hysteresis?

A

Energy is lost by the material in stretching, which results in its temperature increasing

91
Q

What is the law of conservation of energy?

A

Total energy of isolated system is constant

92
Q

What is meant by thermal equilibrium?

A

The condition under which two substances in physical contact with each other exchange no heat energy

93
Q

What is thermal capacity?

A

The amount of heat energy required to raise the temperature of one kilogram of the substance by one degree Celsius

94
Q

What does the ‘W’ in the first law of thermodynamics stand for?

A

Work done

95
Q

The temperature of the air in the barrel increases as the tyre is pumped up. The friction is the pump is negligible. Explain why the temperature of the air in the barrel increases.

A

The air is compressed when the user of the pump pushes down on the pump so the volume decreases which makes the air pressure increase. Work is also being done on the gas so the air particles have increased kinetic energy from the moving piston

96
Q

How does the compressor affect the refrigerator’s efficiency as a heat pump?

A

The compressor heats up when on. It also compresses the vapour to form a liquid. This means lost energy is wasted when it runs so it is not very efficient because of the wasted energy

97
Q

How does the condenser coils affect the refrigerator’s efficiency as a heat pump?

A

Heat is radiated from condenser coils which wastes energy and heat is conducted which reduces efficiency

98
Q

How does the expansion device affect the refrigerator’s efficiency as a heat pump?

A

The expansion device liquid adiabatically to form a gas. Gas leaving is cooler than liquid entering. This is the most efficient part of the refrigerator

99
Q

How do the evaporator coils affect the refrigerator’s efficiency as a heat pump?

A

There’s a change of state which needs heat energy input and heat energy is taken from the inside of the refrigerator to produce vapour. This means the efficiency depends on how fast heat can be extracted from the coils.

100
Q

What two states are fluids?

A

Liquids and gases

101
Q

What can a fluid do when flowing?

A

Transmit pressure, transfer heat, deliver a substance to a new location

102
Q

What is laminar flow?

A

Slow gentle flow of fluid where the motion occurs in one direction

103
Q

What are streamlines?

A

Parallel lines of flow

104
Q

What is turbulent flow?

A

Turbulent flow is when obstacles/sharp objects create turbulence in fluid flow and the drag forces become larger

105
Q

What do the streamlines look like with turbulent flow?

A

They mix and cross

106
Q

What is the correlation between speed of fluid and turbulence?

A

The faster a fluid flows, the more likely there is to be turbulence

107
Q

What does the closeness of streamlines show us?

A

Speed of flow. The closer the lines are, the faster the fluid

108
Q

What is viscosity?

A

Viscosity is a measure of how much a liquid resists flowing

109
Q

What is low viscosity?

A

Flows with little resistance. Liquid is ‘thinner’. Example: water

110
Q

What is high viscosity?

A

Flows with resistance. Liquid is ‘thicker’. Examples: tar, syrup

111
Q

What are the streamlines going to look like for a high viscosity flow?

A

Far apart and slower (Laminar flow unless turbulence is mentioned)

112
Q

What are the streamlines going to look like for a low viscosity flow?

A

Close apart

113
Q

What is the effect of temperature on viscosity?

A

Viscosity reduces at higher temperatures because there are fewer forces between layers

114
Q

What is viscous drag?

A

Viscous drag is the resistance to the flow of a fluid. It is a kind of internal friction between the layers.

115
Q

What is the correlation between viscous drag and velocity?

A

As the velocity increases, the viscous drag increases

116
Q

Is there more viscous drag in turbulent flow than in lamina flow?

A

No

117
Q

Liquids are incompressible. Why?

A

Due to less intermolecular force of attraction, they acquire the shape of the container in which they are kept. The volume of the liquid doesn’t change with pressure

118
Q

What is volume flow rate?

A

Volume flow rate is the mass of fluid flowing per second

119
Q

Is volume flow rate constant for an incompressible liquid?

A

Yes

120
Q

What is the link between the width of a pipe and the fluid flow rate?

A

If a pipe narrows, the fluid flow rate increases

121
Q

Car electrical systems use copper. Copper is described as being ductile. Explain the term ductile.

A

Copper can be pulled/stretched without breaking therefore can be made into wires because these layers of atoms can slide over each other

122
Q

Roofing lead is used as a building material. Explain how creep can cause roofing lead to become damaged

A

Creep is deformation due to mechanical stress. In a roof it’s caused by weather changes. This produces a change in length/shape over time

123
Q

Give the relationship between speed of fluid & internal pressure

A

The higher the speed, the lower the internal pressure

124
Q

What does Bernoulli’s principle state?

A

An increase in the speed of a fluid occurs simultaneously with a decrease in pressure/potential energy

125
Q

What is a Newtonian fluid?

A

A fluid that follows Newton’s law of viscosity

126
Q

In terms of non-newtonian fluids, why do people shake a ketchup bottle?

A

Because it becomes less viscous over time when shaken, so when the ketchup is too thick people shake it to make it thinner.

127
Q

The fact that modern matte paints stay on the wall when you paint it shows they must be shear thinning. Explain.

A

When being brushed it’s very runny so it slides easily onto the walls. When you stop brushing it it stops being runny so it doesn’t slide down the wall.

128
Q

Why does quicksand appear to be solid until you step in it?

A

The viscosity decreases with a rise in the rate of shear strain. There’s a rise in the rate of shear strain when you step onto quicksand which is why the viscosity decreases, revealing that it is not a solid.

129
Q

What is viscous drag?

A

Viscous drag is the drag force felt by an object moving through a fluid due to the viscosity of the fluid

BTEC Science (3 decks)

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