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 ↓


Temperature scales


Temperature is a measure of the average kinetic energy of the particles in a substance. It tells us how hot or cold something is. Different scales have been developed to measure temperature, and each has its own specific use depending on the context. The most commonly used scales for measuring temperature are Celsius (°C), Fahrenheit (°F), and Kelvin (K). Each scale has its own unique starting point known as the zero point and its own increment unit.

Celsius scale

The Celsius scale, also known as the centigrade scale, is widely used to measure temperatures on a daily basis around the world. This scale is based on the phase changes of water:

  • The freezing point of water is 0°C.
  • The boiling point of water is 100°C.

One degree Celsius is equal to one Kelvin. The Celsius scale is convenient for everyday life because it is so closely associated with water, which is an important substance in many contexts.

        V = IR

Where V is the voltage, I is the current, and R is the resistance.

Consider an example: if we are told that the temperature outside is 20°C, we can comfortably say that it is a mild and pleasant day, since it is approximately equal to the room temperature.

Fahrenheit scale

The Fahrenheit scale is used primarily in the United States. It is based on:

  • The freezing point of water is 32°F.
  • The boiling point of water is 212°F.

This scale was designed to reflect the working temperature range of most places. To convert temperatures between Celsius and Fahrenheit, we use the following formula:

        F = (C × 9/5) + 32

For example, if your temperature is 25°C and you want to know what it is in Fahrenheit, you would calculate:

        F = (25 × 9/5) + 32 = 77°F

Thus, 25°C is equal to 77°F.

212°F 32°F 100 degrees Celsius 0 °C

Kelvin scale

The Kelvin scale is a scientific scale for measuring temperature. It is used especially in scientific calculations and experiments. The zero point of the Kelvin scale is absolute zero, the point at which particle motion almost stops. The Kelvin scale is related to the Celsius scale as follows:

  • 0 K is absolute zero.
  • The freezing point of water is 273.15 K.
  • The boiling point of water is 373.15 K.

Conversion between Celsius and Kelvin is simple:

        K = C + 273.15

Suppose we want to find the Kelvin equivalent of 25°C:

        K = 25 + 273.15 = 298.15 K

Scientists often prefer the Kelvin scale because of its absolute nature and ease of calculation.

373.15K 273.15K 100 degrees Celsius 0 °C

Comparison of temperature scales

Let's compare the three scales with each other:

  • Celsius: freezing point 0°C, boiling point 100°C
  • Fahrenheit: Freezing point 32°F, Boiling point 212°F
  • Kelvin: Freezing point 273.15 K, Boiling point 373.15 K

The comparison on the phase change of water is as follows:

State Celsius (°C) Fahrenheit (°F) Kelvin (K)
Freezing point 0 °C 32°F 273.15 K
Boiling point 100 degrees Celsius 212°F 373.15 K

Practical example

Consider an everyday situation such as the temperature of a hot cup of coffee. If the temperature of the coffee is 70°C, you can convert it like this:

In Fahrenheit:

        F = (70 × 9/5) + 32 = 158°F

For Kelvin:

        K = 70 + 273.15 = 343.15 K

Why different scales?

The existence of different temperature scales arises from the history and development of thermodynamics and the need for convenience in different regions of the world. Different scales suit different needs:

  • Celsius is practical for everyday use and is followed in most of the world.
  • The use of Fahrenheit for domestic purposes is more prevalent in regions such as the United States, as it provides better distinction for interpreting weather.
  • The Kelvin is essential in scientific contexts because it allows for absolute temperature measurement and is fully alignable with physical laws such as thermodynamics.

Conclusion

Each temperature scale serves its own specific purpose, whether in daily use, regional preferences, or scientific research, helping us understand and interpret temperature, which is an important aspect of everyday life and the physical world. Understanding these scales, their relationships, and their applications is fundamental in connecting our sensory experience of temperature to numerical data.


Grade 9 → 3.1.3


U
username
0%
completed in Grade 9

← Prev (3.1.2)
Temperature measurement
Next (3.2) →
Heat transfer

Comments 



Temperature scales

https://www.physicsflow.com/g9/3.1.3?pfal=en