Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 ↓


Heat and Thermodynamics


Introduction

Heat and thermodynamics are fundamental concepts that play a vital role in understanding the natural world. These concepts explain how energy is transferred and transformed, which affects the behaviour of matter. In this lesson, we will discuss the basics of heat and thermodynamics, cover key principles, formulas, and examples to provide a comprehensive understanding of the subject. Our goal is to simplify these concepts for Class 9 students, making them accessible and engaging.

What is heat?

Heat is a form of energy that is transferred between systems or objects due to a temperature difference. When you touch a hot pan, the heat you feel is the heat coming from the pan to your hand. Heat always flows from a hotter object to a cooler object, and this transfer continues until thermal equilibrium is reached, which means the two objects are at the same temperature.

Temperature vs heat

It's important to understand the difference between temperature and heat. Although these terms are often used interchangeably, they are not the same:

  • Temperature: It is a measure of the average kinetic energy of the particles in a substance. It is the way we express how hot or cold something is.
  • Heat: It is the transfer of thermal energy from one object to another.

For example, if you have two containers of water, one with a higher temperature and the other with a lower temperature, the hot water has a greater average kinetic energy per particle than the cold water. This difference is essential in the study of heat and thermodynamics.

Methods of heat transfer

Heat can be transferred in three main ways: conduction, convection, and radiation. Let's take a look at each:

Conductivity

Conduction is the transfer of heat through direct contact. When molecules in a substance vibrate, they transfer energy to neighboring molecules, causing them to vibrate as well. Think of conduction like a chain reaction. A simple example is a metal spoon in a hot liquid. The molecules of the spoon gain kinetic energy from the hot liquid and transfer the energy to the spoon.

Q = -kA (dT/dx)

Here, Q is the heat transfer per unit time, k is the thermal conductivity of the material, A is the area, and dT/dx is the temperature gradient.

Convection

Convection is the transfer of heat through a fluid (liquid or gas) by the movement of the fluid. When a fluid is heated, it expands, becomes less dense and rises. As it rises, cooler fluid moves in to take its place. This circulation pattern creates a convection current. You can see convection if you watch water boiling: the hot water rises while the cooler water sinks.

Radiation

Radiation is the transfer of heat via electromagnetic waves. Radiation doesn't require a medium, so heat can travel through the vacuum of space. All objects emit radiation in some form, but a classic example is the heat from the sun that warms the Earth.

Unlike conduction and convection, radiation does not require matter to transfer energy.

Thermodynamics

Thermodynamics is the study of the relationship between heat, work, and energy. It includes four main laws that describe how energy moves and changes form.

First law of thermodynamics

The first law, also called the law of conservation of energy, states that energy cannot be created or destroyed. Instead, energy can only be transferred or transformed from one form to another. The formula is expressed as follows:

ΔU = Q - W

Here, ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.

Second law of thermodynamics

The second law of thermodynamics states that the entropy or disorder of an isolated system always increases over time. This law explains why some processes are irreversible, emphasizing that energy transformations are not 100% efficient.

Third law of thermodynamics

This law states that as the temperature of a perfect crystal approaches absolute zero, its entropy approaches zero. This law explains the behaviour of matter at very low temperatures, helping us understand the limits of cooling substances.

Zeroth law of thermodynamics

The zeroth law states that if two systems are in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other. This law forms the basis of temperature measurement.

Work, heat and internal energy

To understand the basics of thermodynamics, we need to understand the relationship between work, heat, and internal energy. Work and heat are the two main forms of energy transfer. Work involves moving an object by a force, while heat describes the transfer of energy due to a temperature difference. Internal energy is the total energy contained within a system.

Heat engines and refrigerators

Heat engines are devices that convert heat energy into mechanical work. A common example of this is the steam engine. Refrigerators, on the other hand, use work to transfer heat from a cold area to a hot area, essentially moving heat against its natural flow. Using the principles of thermodynamics, we can understand how these devices work and what limitations they face.

Conclusion

Understanding heat and thermodynamics is essential to understand the principles of energy transfer and transformation. From the movement of heat in our daily lives to the operation of complex machinery, these concepts are fundamental in many scientific and engineering applications. The principles in this lesson provide a foundational understanding that will aid further study in physics and related fields.

Visual example

Example of conduction

hot side the cool side heat flow

Example of convection

rising warm air cold sinking air

Example of radiation

Sun radiated heat

Examples for practice

Example 1

Consider a metal rod with one end placed in a flame. Explain how heat is transmitted from one end of the rod to the other.

Example 2

Describe the convection process taking place in a pot of boiling water.

Example 3

How does a thermos bottle minimize heat transfer by conduction, convection, and radiation to keep a beverage hot or cold?

Example 4

If you have a cup of coffee at 80°C and the room temperature is 20°C, explain how the first law of thermodynamics applies as the coffee cools.


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Heat and Thermodynamics

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