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Wize University Physics Textbook (Master) > Heat and Temperature

Temperature vs Heat

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Thermal Equilibrium

  • Temperature can be interpreted as the average kinetic energy of the molecules of a material
  • High temperature corresponds to high kinetic energy
  • A thermometer is a device to measure the temperature of an object

  • When you put a hot body ‘A’ in contact with a cold body ‘B’, interactions between these two bodies will occur eliminating the temperature difference between them
  • At the point where there is no more interaction, the system of the two bodies is said to be in a steady state which is called thermal equilibrium
  • At thermal equilibrium, ‘A’ and ‘B’ have the same temperature
  • Heat flow or heat transfer is the energy transfer that happens only due to a temperature difference
  • The Zeroth Law of Thermodynamics states that if ‘C’ is in thermal equilibrium with ‘A’ and ‘B’, then ‘A’ is also in thermal equilibrium with ‘B’


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Temperature Scales

1. Celsius Temperature Scale
  • We set zero to the freezing temperature of pure water
  • We set 100 to the boiling point of pure water
  • Divide the distance between these two points into 100 equal degrees
2. Fahrenheit Temperature Scale
  • The freezing temperature of water is 32 ºF
  • The boiling temperature of water is 212 ºF
  • The conversion relation between temperature in degrees of Celsius and degrees of Fahrenheit is:
TF=95TC+32°T_F=\frac{9}{5}T_C+32\degree
3. Kelvin Temperature Scale
  • The units are the same size as those in the Celsius scale
  • The zero of temperature at Kelvin scale is equal to −273.15°C-273.15\degree C. This point is called absolute zero
  • The relation between temperature in Kelvin scale and Celsius scale is:
TK=TC+273.15°T_K=T_C+273.15\degree
  • Kelvin is the standard unit of temperature
  • Since the size of units are the same in Kelvin and Celsius temperature scales:
ΔTK=ΔTC\Delta T_K=\Delta T_C



The temperature difference between the inside and outside of a home on a cold winter day is 50oF. Express the difference on

a) Celsius Scale
b) Kelvin Scale

a) TF=95TC+32°FT_F=\frac{9}{5}T_C+32\degree F

TC=59(TF−32°F)T_C=\frac{5}{9}\left(T_F-32\degree F\right)

TC=59(50−32)T_C=\frac{5}{9}\left(50-32\right)

TC=59(18)2T_C=\frac{5}{\cancel{9}}\left(\cancel{18}\right)^{2}

TC=10°CT_C=10\degree C

b) TC=T−273.15T_C=T-273.15

T=TC+273.15T=T_C+273.15

T=10+273.15T=10+273.15

T=283.15°KT=283.15\degree K
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Peter was not feeling well. He checked his body temperature using a thermometer, it was 40oC. What is this temperature on the Fahrenheit scale? Do you think Peter is seriously ill!

Extra Practice
Temperature Scales
Peter was not feeling well. He checked his body temperature using a thermometer, it was 40oC. What is this temperature on the Fahrenheit scale? Do you think Peter is seriously ill!
A mercury thermometer sits in a glass of water for a very long time. The temperature reads 30 degrees. What can we conclude for this?
Temperature vs. Heat
If two objects are put together one is 100 degrees and one is 50 degrees. What will the systems final temperature be?
New Practice Question
The following diagram shows the heating process of 200 𝑔 of an unknown
substance at constant rate. The substance is gas at 40℃. (Cgas=1500  Jkg⋅K)\left(C_{gas}=1500\ \ \frac{J}{kg\cdot K}\right)
a. What is the power of heating? input your answer in J/S, to 2 sig. figs., do NOT include units.
Practice Question 4
One of the hottest temperature ever recorded on the surface of earth was 134oF in the Death valley.
Thermal energy
Compare a huge ice-berg to a red hot piece of metal (fist sized) which of the following is true?
How much heat must be absorbed by 375 grams of water to raise its temperature by 25° C?
Do not include units in your answer.
Round your answer to 2 sig figs and type your answer in scientific notation (ex. 1.2⋅1061.2\cdot10^6)
A sample absorbed 2×102J2\times 10^2 J of heat energy and its temperature is increased by 4 K. Calculate the number of moles of the sample if its molar heat capacity is 75.1 J/K.mole.
Liquid helium boiling point is -268.9oC. What is this temperature in oF and K.
Practice Question 3
a) At what temperature do the Fahrenheit and Celsius scales have the same numerical value?
b) At what temperature do the Fahrenheit and Kelvin scales have the same numerical value?
Practice Question 1
How are heat and temperature related?
Temperature Scales
Peter was not feeling well. He checked his body temperature using a thermometer, it was 40oC. What is this temperature on the Fahrenheit scale? Do you think Peter is seriously ill!