NCERT Class 11 Physics Physics Part-II: Chapter 3 — 1 INTRODUCTION
This chapter introduces the fundamental concepts of thermal properties of matter, starting with common notions of heat and temperature. It defines temperature as a measure of hotness or coldness and heat as energy transferred due to temperature difference. The chapter explains how thermometers work, using physical properties like volume expansion of liquids (mercury, alcohol) or gas behavior. It details the calibration of thermometers using fixed points like the ice point (0°C) and steam point (100°C) and provides the conversion formula between Celsius and Fahrenheit scales. The ideal-gas equation and absolute temperature are introduced, referencing Boyle's and Charles' laws, which describe gas behavior at low densities. This foundational knowledge is crucial for understanding various thermal phenomena and their applications in physics and everyday life.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Physics |
| Book | Physics Part-II |
| Chapter | Chapter 3 — 1 INTRODUCTION |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 5 minutes |
| Word count | 978 |
Learning outcomes
- Define and differentiate between heat and temperature.
- Understand the principles behind temperature measurement using thermometers.
- Explain the relationship between Celsius and Fahrenheit temperature scales.
- Introduce the ideal-gas equation and the concept of absolute temperature.
- Describe the basic laws governing gas behavior (Boyle's Law, Charles' Law).
Vocabulary
| Word | Meaning |
|---|---|
| Hotness | The degree to which something is hot. |
| Coldness | The degree to which something is cold. |
| Heat | Form of energy transferred between systems due to temperature difference. |
| Temperature | A measure of hotness or coldness of a body. |
| Thermometer | An instrument used to measure temperature. |
| Ice point | The temperature at which pure water freezes under standard pressure (0°C). |
| Steam point | The temperature at which pure water boils under standard pressure (100°C). |
| Fahrenheit scale | A temperature scale where water freezes at 32°F and boils at 212°F. |
| Celsius scale | A temperature scale where water freezes at 0°C and boils at 100°C. |
| Absolute temperature | Temperature measured on a scale where absolute zero is the lowest possible temperature (Kelvin scale). |
| Boyle's law | At constant temperature, the pressure of a gas is inversely proportional to its volume. |
| Charles' law | At constant pressure, the volume of a gas is directly proportional to its absolute temperature. |
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Practice questions
- What is the difference between heat and temperature? Answer: Temperature is a measure of hotness or coldness, while heat is the energy transferred between systems due to a temperature difference.
- Name two common fixed points used for calibrating thermometers. Answer: The ice point (freezing point of water) and the steam point (boiling point of water) are two common fixed points.
- What is the SI unit of temperature? Answer: The SI unit of temperature is Kelvin (K).
- State Boyle's Law. Answer: Boyle's Law states that at a constant temperature, the pressure and volume of a given mass of gas are inversely proportional (PV = constant).
- Convert 50°C to Fahrenheit. Answer: Using the formula tF = (9/5)tC + 32, 50°C is (9/5)*50 + 32 = 90 + 32 = 122°F.
Practice MCQs
Q1. Which of the following is a measure of 'hotness' or 'coldness'?
Explanation: Temperature is defined as the measure of hotness or coldness of a body.
Q2. What is the SI unit of heat energy?
Explanation: The SI unit for heat energy transferred is the Joule (J).
Q3. On the Celsius scale, the freezing point of water is:
Explanation: The freezing point of pure water at standard pressure is defined as 0°C on the Celsius scale.
Q4. Which law states that at constant temperature, PV = constant for a gas?
Explanation: Boyle's Law describes the inverse relationship between pressure and volume of a gas at constant temperature.
Q5. A liquid-in-glass thermometer commonly uses the expansion of which substances?
Explanation: Mercury and alcohol are commonly used in liquid-in-glass thermometers due to their significant volume expansion with temperature.
Q6. The steam point of water on the Fahrenheit scale is:
Explanation: On the Fahrenheit scale, the boiling point of water (steam point) is 212°F.
Frequently asked questions
What is the main difference between heat and temperature?
Temperature is a measure of the average kinetic energy of particles in a substance (indicating hotness/coldness), while heat is the transfer of thermal energy between objects due to a temperature difference.
How are thermometers calibrated?
Thermometers are calibrated using two fixed reference points, typically the freezing point (ice point) and boiling point (steam point) of pure water at standard pressure.
What is the relationship between Celsius and Fahrenheit?
The relationship is given by the formula: tF = (9/5)tC + 32, or tC = (5/9)(tF - 32).
What is absolute temperature?
Absolute temperature is measured on a scale where absolute zero (0 Kelvin) is the theoretical lowest possible temperature. It is related to Celsius by T(K) = t(°C) + 273.15.
What does Boyle's Law state?
Boyle's Law states that for a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume (PV = constant).
What does Charles' Law state?
Charles' Law states that for a fixed mass of gas at constant pressure, the volume is directly proportional to its absolute temperature (V/T = constant).
Why are low-density gases important for understanding absolute temperature?
Low-density gases exhibit behavior closer to ideal gases, making their expansion properties more consistent and predictable, which is crucial for defining absolute temperature scales accurately.
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NCERT Class 11 Physics — Physics Part-II — Chapter 3 — 1 INTRODUCTION. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.