Physics · Class 11 Science

Ch 10Thermal Properties of Matter — Class 11 Physics, concept-first.

We all carry an intuitive sense of what "hot" and "cold" mean. A kettle of boiling water feels hot; a block of ice feels cold. Temperature is the physical quantity that measures this "hotness" — it tells us how hot or cold a body is relative to some standard. But common sense alone is not enough for physics.

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Thermal Expansion Coefficient

Think about a metal railway track on a summer day. The track is laid in sections with small gaps between them. On a hot afternoon, those gaps get smaller — sometimes the track even buckles.

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10.1

Introduction

We all carry an intuitive sense of what "hot" and "cold" mean. A kettle of boiling water feels hot; a block of ice feels cold.

10.2

Temperature and Heat

Temperature is a relative measure — an indication of how hot or cold something is. A hot utensil has a high temperature; an ice cube has a low temperature.

10.3

Measurement of Temperature

Temperature is a measure of how hot or cold an object is. But to measure it quantitatively, we need a device that exploits a physical property that changes predictably with temperature.

10.4

Ideal-gas Equation and Absolute Temperature

The behaviour of gases under varying conditions of pressure, volume, and temperature has been studied for centuries.

10.5

Thermal Expansion

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Most substances expand when heated and contract when cooled. This phenomenon — the change in size or volume of a material in response to a change in temperature — is called thermal expansion.

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Example 10.1Show that the coefficient of area expansion, $(\Delta A/A)/\Delta T$, of a rectangular sheet of the solid is twice its linear expansivity, $…Preview

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Example 10.2A blacksmith fixes iron ring on the rim of the wooden wheel of a horse cart. The diameter of the rim and the iron ring are $5.243\ \text{m}$…Preview

10.6

Specific Heat Capacity

When you supply heat to a substance, its temperature usually rises. The amount of heat needed to raise the temperature of a given body by one degree (1 °C or 1 K) is called its heat capacity (often de…

10.7

Calorimetry

When two bodies at different temperatures are placed in thermal contact, heat flows from the hotter body to the colder one.

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Example 10.3A sphere of $0.047\ \text{kg}$ aluminium is placed for sufficient time in a vessel containing boiling water, so that the sphere is at $100\…Preview

10.8

Change of State

When you heat a solid, its temperature rises steadily — until it reaches a certain point. Then something remarkable happens: the temperature stops rising, even though you keep adding heat.

10.8.1

Latent Heat

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Matter exists in three common states — solid, liquid, and gas. A change from one state to another is not a gradual, continuous process at the microscopic level.

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Example 10.4When $0.15\ \text{kg}$ of ice at $0\ ^\circ\text{C}$ is mixed with $0.30\ \text{kg}$ of water at $50\ ^\circ\text{C}$ in a container, the re…Preview

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Example 10.5Calculate the heat required to convert $3\ \text{kg}$ of ice at $-12\ ^\circ\text{C}$ kept in a calorimeter to steam at $100\ ^\circ\text{C}…Preview

10.9

Heat Transfer

Heat moves from a hotter body to a colder one. There are exactly three ways this happens: conduction, convection, and radiation.

10.9.1

Conduction

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Conduction is the transfer of heat through a material without any bulk movement of the material itself.

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Example 10.6What is the temperature of the steel-copper junction in the steady state of the system shown in Fig. 10.15. Length of the steel rod $= 15.0\…Preview

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Example 10.7An iron bar ($L_1 = 0.1\ \text{m}$, $A_1 = 0.02\ \text{m}^{2}$, $K_1 = 79\ \text{W m}^{-1}\ \text{K}^{-1}$) and a brass bar ($L_2 = 0.1\ \te…Preview

10.9.2

Convection

Heat transfer through a fluid — whether liquid or gas — happens by a fundamentally different mechanism than conduction.

10.9.3

Radiation

Heat can travel through empty space. That is the central fact that sets radiation apart from conduction and convection.

10.9.4

Blackbody Radiation

Thermal radiation is not confined to a single wavelength. At any given temperature, it is spread over a continuous range of wavelengths, and the amount of energy carried differs from one wavelength to…

10.10

Newton's Law of Cooling

Every hot object left to itself eventually reaches the temperature of its surroundings. A cup of tea on a table, a hot pan taken off the stove, or a heated metal block in a room — all cool down over t…

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Example 10.8A pan filled with hot food cools from $94\ ^\circ\text{C}$ to $86\ ^\circ\text{C}$ in $2$ minutes when the room temperature is at $20\ ^\cir…Preview

Summary

- Temperature is the measure of hotness; heat is energy in transit due to a temperature difference. - The Celsius, Fahrenheit, and Kelvin scales are related by: and .

Points to Ponder

1. The equation and the assignment for the triple point of water are exact by definition. Because the triple point is now the single fixed point (it has a unique, reproducible temperature), the meltin…

Exercises

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Exemplar Problems

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