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 → Temperature and heat ↓


Concept of heat and temperature


Understanding the nature of heat and temperature is very important to understand the basic principles of physics and thermodynamics. Although they are interrelated, heat and temperature are different concepts that describe different physical phenomena.

Definitions and basic concepts

Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance. It tells us how hot or cold something is. The higher the temperature, the more energy the particles have and the faster they move.

Temperature is measured in degrees using various scales, the most common being Celsius (°C), Fahrenheit (°F), and Kelvin (K). The Kelvin scale is the SI unit for temperature and is often used in scientific contexts. Zero Kelvin (0 K) is called absolute zero, the point at which all molecular motion stops.

Heat

Heat is a form of energy that is transferred between objects due to a difference in temperature. It always flows from the hotter object to the cooler object until thermal equilibrium is reached – that is, until they reach the same temperature.

In the International System of Units (SI), heat is measured in joules (J), although calories can also be used in other contexts.

Visualization of temperature and heat

Cold water Hot water Boiled water

The visualization shows that heat content and temperature are two different phenomena. Even though both boiling water and hot water look similar in appearance, they exist at different energy levels and thus have different temperatures and heat energies.

Main differences between heat and temperature

  • Nature: Temperature is a measurement that affects the thermodynamic state of a system. Heat is energy transferred due to a temperature difference.
  • Measurement: Temperature is measured using a thermometer, while heat is usually measured in joules using a calorimeter.
  • Properties: Temperature is an intensive property (it does not depend on the amount of matter). Heat is an extensive property (it depends on the amount of matter).

Equation of heat transfer

The heat transferred during a change in temperature is given by the formula:

Q = mcΔT

Where:

  • Q is the heat energy transferred in joules (J).
  • m is the mass of the substance in kilograms (kg).
  • c is the specific heat capacity (joules per kilogram per degree Celsius) (J/(kg°C)).
  • ΔT (delta T) is the change in temperature in degrees Celsius (°C).

Examples to clarify concepts

Example 1: Heating water

If you heat 2 kg of water from 20°C to 80°C, we can calculate the energy required as follows:

m = 2 kg 
c = 4,186 J/kg°C (specific heat of water) 
ΔT = 80°C - 20°C = 60°C
Q = mcΔT 
Q = 2 kg * 4,186 J/kg°C * 60°C
Q = 502,320 J

The heat energy required is 502,320 joules.

Example 2: Melting ice

Consider 1 kg of ice at 0°C. Melting the ice would require a different calculation involving latent heat (energy absorbed during a phase change without a change in temperature).

m = 1 kg 
L_f = 334,000 J/kg (latent heat of fusion for ice) 
Q = m * L_f 
Q = 1 kg * 334,000 J/kg 
Q = 334,000 J

The heat energy needed to melt the ice is 334,000 joules.

Relation between heat and temperature

Whenever heat is transferred to a substance, one of two things can happen:

  1. Temperature change: The temperature of the object increases, which corresponds to an increase in the average kinetic energy of its particles.
  2. Phase change: The object remains at a constant temperature as it undergoes a phase change (e.g., ice melting into water). Here, the heat energy goes into breaking intermolecular forces rather than raising the temperature.

Specific heat capacity

Specific heat capacity is the amount of heat required to raise the temperature of 1 kg of a substance by 1 degree Celsius. It varies in different materials and is an intrinsic property of the substance.

The ability of a material to absorb heat varies depending on how quickly it heats up or cools down. For example:

Material specific heat capacity (Joule/kg°C),
Water 4,186
Copper 385
Iron 449

If you have two metal rods, one of copper and the other of iron, both at room temperature, and you apply the same amount of heat energy to both, the copper rod will heat up more quickly than the iron rod because of its lower specific heat capacity.

Thermal equilibrium

When two objects with different temperatures come into contact, heat will flow from the hotter object to the colder object until they both reach the same temperature. This common temperature is called thermal equilibrium.

Consider dropping a hot metal spoon into a cup of cold water. Over time, the spoon cools while the water heats up. Eventually, both the spoon and the water reach the same temperature—the point of thermal equilibrium.

Practical applications

The concepts of heat and temperature are important in a variety of practical applications, ranging from climate control in homes using heaters and air conditioners to industrial processes that produce materials with desired thermal properties.

In everyday life, understanding how different materials react to heat can help make informed choices, such as selecting cooking utensils or insulating materials for buildings, where thermal properties are important.

Conclusion

Understanding the difference between heat and temperature helps to understand many scientific and engineering principles. Heat is a form of energy, and temperature is a measurement that depends on the energy distribution among particles, emphasizing the relative and dynamic nature of thermal energy processes.


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Concept of heat and temperature

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