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Chapter 10: Thermal Properties of Matter

Grade 11 Science | Chapter 10

Thermal Properties of Matter

Heat changes size, temperature and state. This chapter covers temperature scales, thermal expansion, specific heat and calorimetry, and the three ways heat travels.

Core Concepts

Key Principles

Worked Examples

Practice Sets

Contents

Introduction: Heat and Temperature

Temperature Scales

Thermal Expansion

Specific Heat Capacity

Calorimetry and Latent Heat

Heat Transfer

Key Reasoning (Principles)

Worked Examples (10)

Practice Sets A to D

10.

Summary and Exam Quick-Check

1. Introduction: Heat and Temperature

Temperature measures how hot or cold a body is, while heat is the energy that flows from a hotter to a colder body because of that difference. Adding heat can raise temperature, expand a body, or change its state. This chapter quantifies each of these effects and the ways heat moves from place to place.

Core idea

Heating a body raises its temperature by Q = m c ΔT, expands it by ΔL = L α ΔT, and at a change of state supplies latent heat. Heat travels by conduction, convection and radiation.

2. Temperature Scales

Temperature is measured on the Celsius and Kelvin scales. Water freezes at 0 degrees Celsius and boils at 100, while the Kelvin scale starts at absolute zero, the lowest possible temperature. The two are simply related: a temperature in kelvin equals the Celsius value plus 273.15, so a change of one degree is the same size on both scales.

3. Thermal Expansion

Most substances expand on heating as their particles vibrate more and move apart. For a rod, the increase in length is ΔL = L α ΔT, where α is the coefficient of linear expansion and ΔT the temperature rise. This is why gaps are left in railway lines and bridges to allow for expansion in hot weather.

Diagram 1 – Thermal Expansion

A rod expanding in length when heated

Fig 1. Heating a rod increases its length by L times alpha times the temperature rise, as its particles move further apart.

4. Specific Heat Capacity

The specific heat capacity c is the heat needed to raise the temperature of one kilogram of a substance by one degree. The heat supplied is Q = m c ΔT, where m is the mass and ΔT the temperature change. Water has an unusually high specific heat, which is why it warms and cools slowly and is used as a coolant.

5. Calorimetry and Latent Heat

Calorimetry measures heat by the principle that, in an insulated system, the heat lost by the hot body equals the heat gained by the cold body. During a change of state, heat is absorbed or released at constant temperature; this is the latent heat, given by Q = m L. Ice melting and water boiling both take in latent heat without any change in temperature.

6. Heat Transfer

Heat travels in three ways. In conduction, energy passes through a material by particle vibrations without the material moving, as along a metal rod. In convection, warm fluid rises and cool fluid sinks, carrying heat with it. In radiation, heat travels as electromagnetic waves and needs no medium, which is how the Sun’s heat reaches the Earth.

Diagram 2 – Three Ways Heat Travels

Conduction through a solid, convection in a fluid, and radiation from a hot source

Fig 2. Conduction passes heat through solids, convection carries it in moving fluids, and radiation sends it as waves needing no medium.

7. Key Reasoning (Principles)

Principle 1: Heat raises temperature by Q = m c ΔT

The heat needed depends on the mass, the specific heat and the temperature change, so a substance with a high specific heat needs more heat for the same rise.

Principle 2: Heat lost equals heat gained

In an insulated mixture, energy is conserved, so the heat given out by the hot body equals the heat taken in by the cold body, which lets us find a final temperature.

Principle 3: A change of state takes latent heat

Melting or boiling absorbs heat at constant temperature, Q = m L, because the energy goes into breaking the bonds between particles rather than raising the temperature.

8. Worked Examples

Example 1

Q: Convert 27 degrees Celsius to kelvin.

▶ Show Solution

K = C + 273.15 = 27 + 273.15.

= 300.15 K (about 300 K).

Answer: About 300 K.

Example 2

Q: Find the heat to raise 2 kg of water by 10 degrees (c = 4200 J/kg per degree).

▶ Show Solution

Q = m c ΔT = 2 × 4200 × 10.

= 84000 J.

Answer: 84000 J.

Example 3

Q: A 1 m rod (α = 1.2 × 10^-5) is heated by 50 degrees. Find the expansion.

▶ Show Solution

ΔL = L α ΔT = 1 × 1.2 × 10^-5 × 50.

= 6 × 10^-4 m.

Answer: 6 × 10^-4 m.

Example 4

Q: Find the heat to melt 0.5 kg of ice (latent heat L = 336000 J/kg).

▶ Show Solution

Q = m L = 0.5 × 336000.

= 168000 J.

Answer: 168000 J.

Example 5

Q: Find the heat to raise 3 kg of a metal (c = 500) by 20 degrees.

▶ Show Solution

Q = 3 × 500 × 20.

= 30000 J.

Answer: 30000 J.

Example 6

Q: Convert 100 degrees Celsius to kelvin.

▶ Show Solution

K = 100 + 273.15.

= 373.15 K.

Answer: 373.15 K.

Example 7

Q: Name the three ways heat travels.

▶ Show Solution

Conduction, convection and radiation.

Answer: Conduction, convection, radiation.

Example 8

Q: Which mode of heat transfer needs no medium?

▶ Show Solution

Radiation travels as electromagnetic waves and needs no medium.

Answer: Radiation.

Example 9

Q: Find the heat to raise 0.5 kg of water by 40 degrees (c = 4200).

▶ Show Solution

Q = 0.5 × 4200 × 40.

= 84000 J.

Answer: 84000 J.

Example 10

Q: Why is water used as a coolant?

▶ Show Solution

Its high specific heat lets it absorb a lot of heat for a small temperature rise.

Answer: Because of its high specific heat.

9. Practice Sets A to D

Set A – Multiple Choice (Basic)

1. A temperature in kelvin equals Celsius plus: (a) 100 (b) 273.15 (c) 32 (d) 0

2. The heat to change temperature is: (a) mL (b) m c ΔT (c) L α ΔT (d) F ÷ A

3. Linear expansion is given by: (a) L α ΔT (b) m c ΔT (c) mL (d) hρg

4. Heat through a solid without it moving is: (a) convection (b) radiation (c) conduction (d) latent heat

5. Heat that needs no medium travels by: (a) conduction (b) convection (c) radiation (d) calorimetry

▶ Reveal Answers

1. (b) 273.15.

2. (b) m c ΔT.

3. (a) L α ΔT.

4. (c) conduction.

5. (c) radiation.

Set B – Short Answer (Understanding)

1. State the difference between heat and temperature.

2. Write the formula for heat needed to change temperature.

3. Write the formula for linear thermal expansion.

4. What is latent heat?

5. Name and describe the three modes of heat transfer.

▶ Reveal Answers

1. Temperature is how hot a body is; heat is the energy that flows due to a temperature difference.

2. Q = m c ΔT.

3. ΔL = L α ΔT.

4. The heat absorbed or released during a change of state at constant temperature, Q = m L.

5. Conduction through solids, convection in moving fluids, radiation as waves needing no medium.

Set C – Application and Reasoning

1. Convert 50 degrees Celsius to kelvin.

2. Find the heat to raise 1 kg of water by 25 degrees (c = 4200).

3. A 2 m rod (α = 1.2 × 10^-5) is heated by 100 degrees. Find the expansion.

4. Find the heat to melt 1 kg of ice (L = 336000).

5. Why are gaps left in railway lines?

▶ Reveal Answers

1. 50 + 273.15 = 323.15 K.

2. Q = 1 × 4200 × 25 = 105000 J.

3. ΔL = 2 × 1.2 × 10^-5 × 100 = 2.4 × 10^-3 m.

4. Q = 1 × 336000 = 336000 J.

5. To allow the rails to expand in hot weather without buckling.

Set D – Higher Order (Challenge)

1. Hot water at 80 degrees is mixed with equal mass at 20 degrees. Find the final temperature (same substance).

2. Find the heat to turn 0.2 kg of ice at 0 degrees into water at 0 degrees (L = 336000).

3. Explain why coastal areas have milder temperatures than inland areas.

4. A 5 kg block of metal (c = 400) cools by 30 degrees. Find the heat released.

5. Explain why latent heat is absorbed without a temperature change.

▶ Reveal Answers

1. Heat lost = heat gained; equal masses and specific heat give the average, (80 + 20) ÷ 2 = 50 degrees.

2. Q = m L = 0.2 × 336000 = 67200 J.

3. Water’s high specific heat means the sea warms and cools slowly, moderating the temperature of nearby land.

4. Q = m c ΔT = 5 × 400 × 30 = 60000 J.

5. Because the energy goes into breaking the bonds between particles during the change of state, not into raising the temperature.

Chapter Summary

Heat and Temperature

Temperature is how hot a body is; heat is energy flowing due to a difference.

Temperature Scales

Kelvin = Celsius + 273.15; equal-sized degrees.

Thermal Expansion

ΔL = L α ΔT; bodies expand on heating.

Specific Heat

Q = m c ΔT; water’s is high.

Latent Heat

Q = m L; absorbed at constant temperature during a state change.

Heat Transfer

Conduction, convection and radiation.

Quantity

Unit

Symbol

Heat to warm

m c ΔT

Expansion

L α ΔT

Latent heat

m L

8-Point Exam Quick-Check

Temperature is how hot a body is; heat is energy flowing due to a difference.

Kelvin = Celsius plus 273.15.

Heat to change temperature: Q = m c delta T.

Linear expansion: delta L = L alpha delta T.

Latent heat Q = m L is absorbed at constant temperature.

Heat lost equals heat gained in an insulated mixture.

Heat travels by conduction, convection and radiation.

Radiation needs no medium; the Sun’s heat reaches us this way.

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Class 11 Physics Chapter 10: Thermal Properties of Matter, Complete Notes and Practice

This revision guide follows the current NCERT Class 11 Physics syllabus and develops the thermal behaviour of matter, covering temperature scales, thermal expansion, specific heat capacity, calorimetry and latent heat, and the three modes of heat transfer, with two diagrams, ten worked examples and graded practice. Visit SchoolRevise.com to revise, practise and excel.