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 → Waves and sound → Waves and their types ↓


Mechanical and electromagnetic waves


Waves are fascinating phenomena that play a vital role in our everyday lives and the universe. They are essentially disturbances that transfer energy from one place to another without causing permanent displacement of the medium in which they travel. To take a deeper look at this, we first classify waves based on certain properties. In this context, the two main categories are mechanical waves and electromagnetic waves.

Mechanical waves

Mechanical waves need a medium – a physical substance – to travel. Without a medium, they cannot propagate. These waves are classified into three types based on the speed of the particles of the medium:

1. Transverse waves

In transverse waves, the particles of the medium move perpendicular to the direction in which the wave itself moves. This type of wave can be seen as ripples on the surface of water. When the wind blows over water, it creates waves, in which each water molecule moves up and down as the wave travels horizontally across the surface.

A classic example of a transverse wave is a wave on a string. Here, if you shake one end of a string up and down, the wave travels along the length of the string, with each section of the string oscillating up and down.

2. Longitudinal waves

Longitudinal waves are characterized by the motion of particles that is parallel to the wave's direction of travel. Think of sound waves traveling through air. When a sound wave moves through air, it creates regions of compression and rarefaction by pushing air molecules together and then pushing them apart.

This phenomenon can be experienced when a tuning fork is struck. The prongs of the tuning fork vibrate, compressing and then expanding the air. The waves travel through the air to your ear, allowing you to hear the sound.

3. Surface waves

Surface waves are a mixture of transverse and longitudinal waves. They usually occur at interfaces between different media, such as the ocean surface. In these types of waves, the particles move in circular paths. This is why objects on the surface move slightly up and down along with the waves.

Surface waves are responsible for the undulating motion seen in oceans when the wind blows. Watching a boat rocking back and forth in the ocean illustrates the effect of surface waves.

Electromagnetic waves

Unlike mechanical waves, electromagnetic waves do not require a medium to travel. They can pass through vacuum (empty space), which is why we can see sunlight passing through the vastness of space. Electromagnetic waves are produced by the vibration of electric charges and are characterized by oscillation of electric and magnetic fields.

The electromagnetic spectrum includes a wide range of waves that vary in wavelength and frequency. Here are some types of electromagnetic waves, which differ based on their wavelength:

1. Radio waves

Radio waves have the longest wavelengths in the electromagnetic spectrum, ranging from about one metre to thousands of kilometres. They are used in communications devices such as radios, televisions and mobile phones. When a radio station broadcasts a signal, it uses radio waves, which travel through the air to your radio receiver, allowing you to hear the station.

2. Microwave

Microwaves have a shorter wavelength than radio waves. They are commonly used for wireless communication. They are most commonly used in microwave ovens, where they are used to heat food by causing the water molecules in the food to vibrate and produce heat through friction.

3. Infrared waves

Infrared waves have a wavelength shorter than microwaves but longer than visible light. They are often experienced as heat. An example of infrared waves is the warmth you feel when standing near a heat source, such as a campfire. Infrared is also used in remote control devices and thermal imaging technology.

4. Visible light

Visible light is a small part of the electromagnetic spectrum and is the range of wavelengths to which the human eye is sensitive. It is the light emitted by a lamp or computer screen. This range includes all the colours of the rainbow, from red to violet, with each colour corresponding to a different wavelength.

5. Ultraviolet waves

Ultraviolet (UV) waves have a shorter wavelength than visible light and can be harmful in large amounts. This is why we wear sunscreen, which protects our skin from the ultraviolet radiation emitted by the sun. However, UV rays can also have beneficial effects, such as helping our bodies make vitamin D when exposed to sunlight.

visible light spectrum

6. X-ray

X-rays have a wavelength even shorter than ultraviolet waves. Medical professionals often use X-rays to examine the inside of the body. This is because X-rays can penetrate flesh but are absorbed by bones, making it easier for doctors to examine bone structures.

7. Gamma rays

Gamma rays have the shortest wavelength and the highest frequency in the electromagnetic spectrum. They carry a lot of energy and can pass through most materials. Gamma rays are produced in nuclear reactions and certain types of radioactive decay. They are used in medicine to treat cancer and in industries for imaging and sterilization.

Comparison of mechanical and electromagnetic waves

Mechanical and electromagnetic waves are both forms of energy transfer, yet they have several key differences:

  • Need for medium: Mechanical waves need a medium to travel, while electromagnetic waves do not.
  • Speed: Electromagnetic waves travel at the speed of light in a vacuum, about 3 x 10^8 meters per second. Mechanical waves, such as sound, travel much slower in air, about 340 meters per second.
  • Propagation: Mechanical waves can be either transverse or longitudinal, while electromagnetic waves are inherently transverse, and their electric and magnetic fields oscillate perpendicular to the direction of propagation.

In short, understanding the types of waves and their behavior helps us understand how energy is transferred from one form to another and how it interacts with different materials. Whether it is the sound of music playing on the radio, the heat of sunlight, or the diagnostic use of an X-ray machine, waves have a profound impact on our daily lives.


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Mechanical and electromagnetic waves

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