LECTURE NOTES · MODULE 02
Heat & Temperature
Thermometry — scales, devices & calibration
DATE 17.06.2026
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LECTURE 02
CLASS: EEE PHYSICS
Heat
Heat is a form of energy. It is the total energy of all the molecules inside a material/substance.
2
Temperature
Temperature is the measurement of heat.
3
Heat Transformation Principle
When two bodies of different temperature come into thermal contact, they exchange heat.
Heat always flows from higher temperature to lower temperature.
HEAT FLOW
HOT
COLD
Heat always flows from the hotter body to the colder body until thermal equilibrium is reached.
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Thermometer
A thermometer is a device by which temperature can be measured.
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Types of Thermometers
Following is the list of thermometers:
i
Constant-Volume (Gas) thermometer
ii
Platinum → Resistance thermometer
iii
Thermo-electric thermometer
PHYSICS · HEAT & TEMPERATURE · LECTURE 2
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HEAT & TEMPERATURE
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iv
Radiation thermometer
v
Optical (pyrometer)
Gas
Resistance
Thermo-electric
Radiation
Optical
Example: common thermometer types used in practice.
Homework — partly unclear
Your notebook has a Bangla homework note here about two bodies of different temperature in
thermal contact, with what looks like an example involving temperature change. The
handwriting in this section wasn't fully legible from the scan, so it's left out to avoid giving you
wrong information. Please check this part with your notebook/teacher, or send a closer photo of
just this line and it can be added in.
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Thermometric Substance
Thermometric substances are materials that can change their physical appearance with
temperature.
Examples
• Mercury
• Alcohol
• Platinum
• Gas
• Copper-Constantan (thermocouple)
• Semiconductor
PHYSICS · HEAT & TEMPERATURE · LECTURE 2
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HEAT & TEMPERATURE
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IC
Mercury
Alcohol
Platinum
Gas
Cu-Constantan
Semicon.
Example: common thermometric substances and the property that changes with heat.
Homework — partly unclear
There's another short homework note here (in Bangla) referencing mercury, platinum, and items
(ii)–(vi) from the list above. This part was also not clearly legible from the scan — worth
double-checking against the original notebook.
Thermometric Property
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Thermometric substances can change their physical appearance with temperature; these
physical appearances are known as thermometric properties.
Examples
• Changes in length, volume, or pressure
• Electrical changes — resistance, thermo-electric effect
• Change in state and colour
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θ
Calibration — Two Fixed Point Method
Every thermometric substance can be associated with a thermometric property at a fixed
temperature. Using the ice point and steam point as two reference (fixed) points, we can
calibrate an unknown temperature.
PHYSICS · HEAT & TEMPERATURE · LECTURE 2
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HEAT & TEMPERATURE
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Steam point
θsteam ,
Xsteam
(100°C)
Unknown
N
θ ,
X
(reading)
Ice point
θice ,
Xice
(0°C)
The two fixed points — ice point (0°C) and steam point (100°C) — bracket the scale; an unknown temperature θ is
read off proportionally between them.
Let:
= temperature of the ice point
•
θ
•
θsteam = temperature of the steam point
•
•
ice
Xice = thermometric property at θice
Xsteam = thermometric property at θsteam
•
θ = unknown temperature, X = thermometric property at θ
•
N = interval between ice point and steam point (θsteam − θice)
EQUATION
(θ − θice) / (θsteam − θice) = (X − Xice) / (Xsteam − Xice)
(θ − θice) / N = (X − Xice) / (Xsteam − Xice)
θ = [(X − Xice) / (Xsteam − Xice)] × N + θice
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HEAT & TEMPERATURE
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This is the equation for the calibration of unknown temperature using two fixed points.
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θ
Calibration — One Fixed Point Method
Equation of the unknown temperature using one fixed point. Let T be the unknown temperature
and Xp be the thermometric property at T. The thermometric property is directly proportional
to the temperature:
EQUATION
Xp ∝ T
Xp = α T
α = Xp / T
where α is the temperature constant (temperature coefficient), and T is the unknown
temperature calculated from one known fixed point.
Typed & redesigned from handwritten class notes (Lecture 2). A couple of short homework lines in Bangla were left as
flagged notes instead of guessed text — happy to fill them in once confirmed.
PHYSICS · HEAT & TEMPERATURE · LECTURE 2
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