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physics gic > Heat > Flashcards

Heat Flashcards

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1
Q

What is heat (2)

A

-Heat is the energy that is transferred between objects because of a temperature difference
-objects are considered to be in thermal contact if heat can flow between them

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2
Q

Explain 3 ways heat can be transferred between a hot object to a cooler one (3)

A

-conduction
-convention
-radiation

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3
Q

State the definition of thermal equilibrium (1)

A

-when objects have the same temperature and no heat flows between them

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4
Q

Explain how heat is exchsnged between a hot object and cold object (3)

A

-when a hot object is brought into thermal contact with a colder object heat is exchsnged
-the hot object cools down and it’s molecules slow down while the hot object warms up
-after sometime if being in thermal contact both objects come into thermal equilibrium

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5
Q

State the zeroth law (1)

A

-if object A is in thermal contact with object B
-and object B is in thermal contact with object C
-then object A and C are in thermal equilibrium with no thermal contact

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6
Q

At what temprature (Celsius) does water freeze (1)

A

0

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7
Q

At what temprature (Celsius) does water boil (1)

A

100

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8
Q

At what temprature (fahrenite ) does water freeze (1)

A

32

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9
Q

At what temprature (farhenite) does water boil (1)

A

212

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10
Q

State the conversion from C to F stating a formula (1)

A

Tf = 9/5 x Tc + 32

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11
Q

State the conversion from F to C stating a formula (1)

A

Tc = 5/9 ( Tf - 32)

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12
Q

State and explain the concept of absolute zero (2)

A

-absolute zero refers to the lowest possible temperature that a system or an object can reach
-it is the point at which the fundamental particle of a substance such as atom or molecules have minimum amount of motion or vibrations

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13
Q

State the relationship between volume and temperature (3)

A

-cooling air from 100 to 0 reduces its volume
-volume of gas is inversely proportional to its temperature at constant pressure
-as the temprature approaches absolute zero the volume of the gas would theoretically be zero

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14
Q

State the relationship between pressure and temprature (2)

A

-pressure in a gas is proportional to its temperature
-they all reach zero pressure at the same temperature called absolute zero

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15
Q

The gas in a constant volume gas thermometer has a pressure of 80kPa at 0C . Assuming ideal gas behavior what is the pressure of a gas at 105C (2)

A

Use Charles law =
P1/T1 = P2/T2

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16
Q

State the conversion from Celsius to kelvin

A

T = Tc + 273.15

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17
Q

When rod 1 is heated by an amount of T it’s length increases by L. If rod 2 which is twice the length as rod 1 and made of the same material is heated by the same amount what happens to its length

A

The rod expands by 2L

18
Q

State the formula for the coefficient of linear expansion (1)

A

Change in length = coefficient of thermal expansion x initial length x change in temperature

19
Q

State and explain bimetallic strips (3)

A

-they are made by bonding two different metals with distinct coefficient of linear expansion
-as the strip is heated or cooled the metals change lengths by different amounts causing the strip to bend
-it is highly sensitive to temperature changes

20
Q

In a bimetallic strip one metal has a larger coefficient of expansion than the other, it is then heated, what effect does it have (1)

A

-when the bimetallic strip is heated, the metal with the higher coefficient of linear expansion will expand more than the one with the lower coefficient

21
Q

State one application of bimetallic strip (2)

A

Thermometer
-the shape changes with the temperature moving the needle to indicate the temperature

22
Q

State the formula for area expansion (1)

A

Change in area = initial area x (2 x coefficient of linear expansion) x change in temperature

23
Q

State the formula for volume expansion (1)

A

Change In volume = initial volume x (3 x coefficient of linear expansion) x change in temperature

24
Q

State and explain why ice is less dense than water (4)

A

-water molecules are polar, this polarity results in hydrogen bonding between water molecules
-in liquid state, water molecules are close together and exhibit hydrogen bonding
-when water freezes into ice, hydrogen bonding becomes more stable and the arrangement is open creating more space between molecules
-the open and hexagonal arrangement in ice results in a lower density which causes it to float in water

25
Q

Why do water pipes burst (1)

A

Water pipes burst due to the expansion of ice forming in them

26
Q

State the definition of kCal (1)

A

-one kilocalorie (kCal) is defined as the amount of heat needed to raise the temperature of 1kg of water from 14.5C to 15.5C

27
Q

How many Joules is one Cal

A

1 cal = 4.186J

28
Q

State the definition of BTU (1)

A

It is the energy required to heat 1 lb of water from 63F to 64F

29
Q

State the conversion from 1Btu to KCal and J (2)

A

1Btu = 0.252kCal = 1055J

30
Q

State the formula for heat (1)

A

Q = mgh

31
Q

State the definition of heat capacity (3)

A

-it is the amount of heat added to it divided by its rise in temperature
-heat capacity depends on the mass

Specific heat capacity = heat / temperature

32
Q

What is a calorimeter (1)

A

-it is a device used to measure the heat exchanged between an object and it’s surrounding

33
Q

What happens when an object is placed into a calorimeter, and how does heat transfer take place between the object and the water until they achieve thermal equilibrium (3)

A

-when an object is placed in the calorimeter heat transfer occurs between the object and the water until they reach thermal equilibrium
-during this process the object either absorbs or releases heat causing a temperature change in the water
-the heat transfer continuous until both, the object and the water reach the same temperature indicating thermal equilibrium
-in an isolated system like calorimeter the total energy remains constant

Q object + Q water = 0

34
Q

State the formula for object and water in calorimeter (1)

A

Q water = mass of water x specific heat capacity of water x (final tempt - intitial tempt)

Q object = mass of object x specific heat capacity of object x (final tempt - intitial tempt)

Final temperature = (mO x cO)+ (mW x cW x tW) / (mO x cO)+ (mW x cW)

35
Q

State the definition of conduction (2)

A
  • It is the flow of heat directly through a physical material
    -in a solid material such as metal rod the particles vibrate and this vibration is passed along to neighboring particles
36
Q

State the relation between thermal conductivity and area, time, length, temperature (4)

A

-as area increases the thermal conductivity increases because wider rod provides more pathways for heat to travel

-as time increases more heat can flow through the rod

-as length increases the thermal conductivity decreases because larger rods provide more resistance for heat to flow

-as temperature difference increases the rate of flow of heat increases

37
Q

State the formula between thermal conductivity and area, time, length, temperature (4)

A

Q = thermal conductivity x area x (temperature difference/ length) x time

38
Q

Why do you feel like the tile is colder than the carpet (2)

A

-tile has a much larger thermal conductivity than the carpet
-more heat flows from your skin to the tile leaving your body cold

39
Q

State and explain on the topic of convention (3)

A

-convection involves the transfer of heat through the movement of fluids (liquids or gases)
-when a fluid is heated it becomes less dense and rises such as warm air
-as it moves it carries heat with it

40
Q

State and explain on the topic of radiation (2)

A

-radiation is the transfer of heat through electromagnetic waves such as infrared radiation
-radiation does not require a material medium for heat transfer
The amount of radiation emitted depends on the temperature and the nature of surface involved

41
Q

State and explain emissivity and state a formula (4)

A

-is a dimensionless number between 0 to 1 that characterizes how effectively an object radiates heat

1 = black color absorbs all heat
0 = white color does not emit any energy

Radiated power = emissivity of an object x 5.57x10^-8 x area x (temperature)^4

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