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Physics 2 > Unit 1 > Flashcards

Unit 1 Flashcards

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1
Q

Thermodynamics

A

the study of heat and its transformation into mechanical energy.

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2
Q

Cold

A

the absence of heat

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3
Q

Heat

A

energy that is transferred from one object to another because of temperature difference.

  • Flow is from warmer substance to cooler.
  • is energy
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4
Q

Temperature

A

Quantity that tells how hot or cold something is compared with a standard.

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5
Q

Latent heat

A

Heat involved in a phase change

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6
Q

Nearly all matter…

A

expands when its temperature increases (are heated) and contracts when temperature decreases (are cooled)

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7
Q

What is temperature related to?

A

The random motions of the molecules in a substance. The higher the temperature of a substance, the faster is the motion of its molecules.

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8
Q

Thermal contact

A

When heat flows from one object or substance to another

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9
Q

Thermal equilibrium

A

When objects in thermal contact with each other reach the same temperature. No heat flows between them.

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10
Q

How a thermometer works

A

Thermometer in contact with substance -> heat flows between them until they have the same temperature.

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11
Q

Internal energy

A

The grand total of all energies inside a substance. When a substance takes in or gives off heat, its internal energy changes.

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12
Q

The amount of heat transferred can be determined by…

A

measuring the temperature change of a known mass of a substance that absorbs the heat.

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13
Q

What do need to specify to quantify heat

A

Mass and kind of substance affected

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14
Q

Calorie

A

The amount of heat required to raise the temperature of 1 gram of water by 1 degree celsius

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15
Q

Kilocalorie

A

1000 calories

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16
Q

What does the capacity of a substance to store heat depend on?

A

Chemical composition

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17
Q

Specific heat capacity of a material

A

The quantity of heat required to raise the temperature of a unite mass of the material by 1 degree.

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18
Q

Bimetallic strip

A

Two strips of different metals are welded or riveted together

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19
Q

Thermostat

A

Uses a bimetallic strip to control temperature.

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20
Q

Conduction

A

Transfer of energy within materials and between different materials that are in direct contact.
-Collisions between particles transfer thermal energy.

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21
Q

Conductors

A

Materials that conduct heat well.

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22
Q

Insulator

A

Any material that is a poor conductor of heat and that delays the transfer of heat.

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23
Q

Convection

A

A means of heat transfer by movement of the heated substance itself, such as by currents in a fluid.
-Heat is transferred by movement of the hotter substance from one place to another

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24
Q

Radiation

A

Energy transmitted by electromagnetic waves.

-heat is transmitted in the form of radiant energy, or electromagnetic waves.

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25
Q

Radiant energy

A

Any energy that is transmitted by radiation. is the energy in electromagnetic waves. It can travel through a vacuum whereas convection and conduction need a physical medium to travel through.

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26
Q

All substances continuously emit…

A

Radiant energy in a mixture of wavelengths.

average frequency f of radiant energy is directly proportional to the Kelvin temperature T of the emitter

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27
Q

Stellar radiation

A

Radiant energy emitted by the stars

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28
Q

Terrestrial radiation

A

Radiant energy that is emitted by Earth

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29
Q

Good emitters of radiant energy are also…

A

Good absorbers. Vice versa for poor emitters

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30
Q

Newton’s law of cooling

A

The colder an object’s surroundings, the faster the object will cool.
-applies for heat
rate of cooling ~ (change in) temperature

31
Q

Greenhouse effect

A

Warming of a planet’s surface due to the trapping of radiation by the planet’s atmosphere.

32
Q

Evaporation

A

Change of phase from liquid to gas that takes place at the surface of a liquid. A process that cools the liquid left behind.

33
Q

Condensation

A

Changing of a gas to a liquid. Warms the area where the liquid forms.

34
Q

Saturated

A

The first substance when any substance containing the maximum amount of another substance

35
Q

Relative humidity

A

Ratio of how much water vapor is in the air to the maximum amount that could be in the air at the same temperature.

36
Q

Evaporation and condensation occur…

A

continuously at equal rates. The molecules and energy leaving a liquid’s surface by evaporation can be counteracted by as many molecules and as much energy returning by condensation.

37
Q

Boiling

A

The change of phase from liquid to gas beneath a liquid’s surface.
-depends on both temperature and pressure

38
Q

Increasing the pressure on the surface of a liquid raises…

A

the boiling point of the liquid.

39
Q

Freezing

A

The change in phase from liquid to solid
-when energy is continually withdrawn from a liquid, molecular motion slows until the forces of attraction between the molecules cause them to get closer to one another.

40
Q

In general, dissolving anything in a liquid…

A

lowers the liquid’s freezing temperature.

41
Q

Lowering the pressure can cause…

A

boiling and freezing to take place at the same time.

42
Q

Regelation

A

Phenomena of melting under pressure and freezing again when pressure is reduced
-can only occur in substances that expand when they freeze

43
Q

Energy must be put into a substance to…

A

change its phase from solid to liquid to gas. Conversely, energy must be extracted from a substance to change its phase from gas to liquid to solid.

44
Q

Heat pump

A

A device that moves heat.

45
Q

Why does 2 liters of boiling water not have twice as great a temperature as 1 liter of boiling water?

A

The temperatures are the same because the average KE is the same, regardless of the volume.

46
Q

Why is it incorrect to say that matter “contains” heat?

A

Matter contains internal energy. Heat is the flow of that energy due to a difference in temperature.

47
Q

What is the difference between a calorie, a Calorie and a Joule?

A

1 Calorie = 1000 calories and 1 Calorie = 4.186 Joules. This is the amount of energy that it takes to raise the temperature of 1 gram of water by 1°C.

48
Q

What does it mean to say that a substance has a high specific heat capacity?

A

It has a large ability to store internal energy. It also means that the substance takes longer to heat up and cool down than substances with low specific heat capacities.
-Water has a very high specific heat capacity.

49
Q

Heat transfer in calories equation

A

Q = mcrT, where m is mass in grams, c is specific heat capacity in cal/g°C and rT is in °C.

50
Q

Why does a piece of room-temperature metal feel cooler to the touch than paper, wood, or cloth?

A

Metal is a good conductor which removes heat quickly whereas wood, paper, and cloth are insulators (poor conductors) and so do not remove heat as quickly. Your body senses change in thermal energy rather that sensing the temperature itself.

51
Q

Why does the direction of coastal winds change from day to night?

A

The land heats up more quickly during the day so the air above the land rises and air is drawn in from the ocean to replace it. At night the land cools more quickly than the water so the water is warmer and air from land moves to replace the rising air over the ocean.

52
Q

How does the radiation that is given off by an object change as the object is heated?

A

As the object gets hotter, it gives off energy with shorter and shorter wavelengths (higher and higher energies).

53
Q

Explain why a candle cannot stay lit in the space shuttle when it is in orbit and the astronauts are floating freely.

A

There is no convection while the space shuttle is in free-fall and a candle depends on the conductive process that moves hot gases upward and brings in fresh oxygen to stay lit.

54
Q

Explain why the hydrogen molecules are moving faster than the oxygen molecules in a mixture of hydrogen gas and oxygen gas.

A

In a mixture, the gases will be at the same temperature and so will have the same average kinetic energy. The hydrogen molecules are much smaller, however, so they must be moving faster in order to have the same KE as the larger oxygen molecules.

55
Q

Why is it incorrect to say that only hot things radiate energy?

A

All objects continually emit radiant energy in a mixture of wavelengths. The hotter an object is, the shorter the wavelength its radiation is. Warm objects (like people) emit infra-red radiation while hot objects (like burning logs or candle flames) emit both heat and light.

56
Q

Heat added to a system =

A

increased internal energy of the system + external work done by the system.

57
Q

As the thermal motion of atoms in a substance approaches zero…

A

the kinetic energy of the atoms approaches zero, and the temperature of the substance approaches a lower limit (the absolute zero of temperature).

58
Q

Absolute zero

A

Temperature at which no more energy can be extracted from a substance and no further lowering of its temperature is possible.

59
Q

First law of thermodynamics

A

Law of conservation of energy applied to thermal systems. Whenever heat is added to a system, it transforms to an equal amount of some other form of energy.

60
Q

System

A

Any group of atoms, molecules, particles, or objects we wish to deal with.

61
Q

Adiabatic

A

Process where a gas is compressed or expanded so that no heat enters or leaves a system.
-For a process to be adiabatic, no heat can enter or leave the system while the process is occurring.

62
Q

What happens when work is done on a gas by adiabatically compressing it?

A

Gas gains internal energy and becomes warmer.

63
Q

Adiabatic form of the first law

A

Change in air temperature ~ pressure change

64
Q

Second law of thermodynamics

A

Heat will never of itself flow from a cold object to a hot object.
-no heat engine can convert all heat input to mechanical energy output.

65
Q

Third law of thermodynamics

A

No system can reach absolute zero.

66
Q

Heat engine

A

Any device that changes internal energy into mechanical work.

67
Q

Carnot efficiency

A

Ideal efficiency. Of a heat engine, it is the ideal maximum percentage of input energy that the engine can convert to work.
Equation: (T(hot) - T(cold))/T(hot)

68
Q

What to natural systems tend to proceed towards?

A

A state of greater disorder.

69
Q

Entropy

A

Measure of the amount of disorder in a system. Disorder increases; entropy increases.

70
Q

Why does antifreeze (or any soluble substance) lower the freezing temperature of water when they are mixed?

A

Foreign particles interfere with the formation of the hexagonal ice structure.

71
Q

Explain how boiling and freezing can occur at the same time.

A

Water boils at 100°C when the air pressure is 1 atmosphere, but if you reduce the air pressure around water, you can boil it at temperatures lower than 100°C. By reducing the pressure you cause boiling at low temps. Boiling is a cooling process which lowers the temperature even further. The water can boil and the vapor can instantly freeze when pressures are low enough.

72
Q

What happens to the internal energy of a system when work is done on it?

A

the internal energy of the system increases.

73
Q

What three processes occur in every heat engine?

A

Every heat engine includes the processes of energy absorption, conversion of some energy to work, and expulsion of the rest of the energy.

74
Q

Under what conditions can entropy decrease in a system?

A

Entropy can decrease when work or other organized energy is added to the system.

Physics 2 (7 decks)

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