Thermometry, Thermal Expansion, and Calorimetry – JEE Physics Made Easy

🌡️ Thermometry, Thermal Expansion, and Calorimetry – JEE Physics in Simple Words

Hey JEE aspirants!

Today we’ll break down three important topics from Thermal Physics:

👉 Thermometry

👉 Thermal Expansion

👉 Calorimetry

Let’s understand these in simple language with examples, formulas, and JEE tips.

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🔥 Part 1: What is Thermometry?

👉 Thermometry = Measurement of Temperature

Thermo = heat

Metry = measurement

So, thermometry means measuring temperature using a thermometer.

🌡️ Types of Thermometers:

Type Description

Mercury Thermometer Uses mercury. Common in labs.

Alcohol Thermometer For low temperatures.

Digital Thermometer Uses sensors and displays temp digitally.

Gas Thermometer Very accurate. Used in experiments.

🔄 Temperature Scales:

Scale Freezing Point Boiling Point Formula

Celsius (°C) 

freezing point of water 0°C

Boiling point of water 100°C 

Fahrenheit (°F) freezing point of water32°F

 Boiling point of water 212°F 

Kelvin (K) freezing point of water273K

 Boiling point of water 373K 

°F = (9/5)°C + 32

K = °C + 273

👉 JEE Tip: Questions often test conversion between °C, °F, and K. So master this type of question.

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🧱 Part 2: What is Thermal Expansion?

When a substance is heated, it expands. That’s thermal expansion.

🔸 3 Types of Thermal Expansion:

1. Linear Expansion – Increase in length

Formula:

ΔL = L₀αΔT

 Hi L₀= original length,  

 α = coefficient of linear expansion,  

ΔT= change in temperature

2. Area Expansion – Increase in area

Formula:

ΔA = A₀βΔT

A₀= original area 

 β =coefficient of areal expansion,  

ΔT= change in temperature

3. Volume Expansion – Increase in volume

Formula: 

ΔV = V₀γΔT

V₀=original volume 

 γ=coefficient of volume expansion,  

ΔT= change in temperature

🔥 Real-Life Examp👉 JEE Tip:

Expect numericals using formulas above.

Also be ready for conceptual questions on real-life expansion examples.

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🥛 Part 3: What is Calorimetry?

Calorimetry = Study of heat transfer between objects.

When a hot object is placed in contact with a cold one, heat flows from hot to cold until thermal equilibrium is reached.

☕ Principle of Calorimetry:

> “Heat lost by hot body = Heat gained by cold body”

Q lost= Qgained

🔸 Formula for Heat:

Q = mcΔT

Where:

Q= heat transferred (in joules)

m= mass

c= specific heat capacity

ΔT= temperature change

🔄 Phase Change Heat:

During melting or boiling, temperature doesn't change — but heat is still absorbed/released.

1. Heat during Fusion (Melting):

Q = m × Lf

Where:

Q = heat absorbed or released (in joules)

m = mass of the substance (in kg or g)

Lf = latent heat of fusion (in J/kg or J/g)

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🧠 Sample JEE Question (Concept + Calculation)

Q: A 1 kg piece of iron at 100°C is dropped into 2 kg of water at 30°C. Final temp is 35°C. Find the specific heat of iron. (Take water’s specific heat = 4200 J/kg°C)

Solution: I want in comments section 

🧾 Summary Table

Topic Key Formula JEE Use

Thermometry °F = (9/5)°C + 32 Conversion Qs

Linear Expansion ΔL = L₀αΔT Direct numericals

Area Expansion ΔA = A₀βΔT Conceptual use

Volume Expansion ΔV = V₀γΔT Real-life examples

Calorimetry mcΔT, mL Heat transfer problems

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💡 Final Motivation

These concepts repeat in JEE Mains and Advanced every year — directly or indirectly. If you master basics + formulas, and practice good numericals, you're good to go!