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


Waves are disturbances that travel through a medium from one place to another. They carry energy and do not necessarily transport matter. Waves are an integral part of the study of physics as they describe various phenomena in fields such as sound, light, and even seismic activity. Understanding the fundamental properties of a wave is very helpful in explaining and predicting wave behavior in different mediums.

Basic properties of waves

Before learning about the different types of waves, it is necessary to understand the basic properties that characterize all waves:

  • Amplitude: It refers to the height of the wave, which is the maximum displacement of the wave from its rest position. It is measured in meters.
  • Wavelength (λ): Wavelength is the distance between two successive points that are in the same phase, such as peak to peak or trough to trough. It is also measured in meters.
  • Frequency (f): Frequency measures how many times waves pass a given point in one second. It is measured in Hertz (Hz).
  • Period (T): The period is the time it takes for one complete cycle of the wave to pass a given point. It is related to the frequency by the formula T = 1/f.
  • Speed (v): Speed is the rate at which the wave travels through a medium and is calculated using the formula
     V = fL

Visualization of waves

To understand how waves work, consider a simple transverse wave traveling in space:

Crest trough l

In the illustration above, the wave oscillates up and down about a central axis, with the crests being the highest points and the troughs being the lowest points.

Types of waves

Waves can be classified based on their characteristics and medium of propagation. The primary types of waves are:

1. Mechanical waves

Mechanical waves require a medium to travel, which can be solid, liquid or gas. These are further divided into transverse and longitudinal waves.

Transverse waves

In transverse waves the particles of the medium move perpendicular to the direction of wave propagation. A common example is a wave on a string:

If you shake the rope or slinky up and down, the waves produced will be transverse, because the oscillations occur at right angles to the direction of motion of the wave.

Longitudinal waves

Unlike transverse waves, in longitudinal waves the particles of the medium move parallel to the direction of wave propagation. A classic example of this is a sound wave:

If you push and pull a slinky in and out horizontally, the regions of compression and rarefaction will help create longitudinal waves.

2. Electromagnetic waves

Electromagnetic waves do not require a medium to travel. They can propagate in a vacuum or any other medium because they are composed of oscillating electric and magnetic fields. Examples include light waves, microwaves, and X-rays. Light waves are typically modeled as a combination of transverse electric and magnetic fields:

electric field Magnetic Field

In electromagnetic waves, the electric field (red) and magnetic field (blue) oscillate perpendicular to each other and to the direction of wave propagation.

3. Surface waves

Surface waves occur at the interface between two different mediums, such as water and air. In these waves, particles move in a circular motion, driven by both transverse and longitudinal wave motion. An everyday example of surface waves can be seen in ocean waves.

The water particles move in tiny circles as the wave passes, demonstrating the unique behavior of surface waves.

Examples in daily life

Sound waves

Sound waves are longitudinal mechanical waves. They propagate through the air and reach our ears. When someone speaks, the vocal cords set air molecules into oscillation, creating a series of compressions and rarefactions that travel through the air:

Example: Clapping produces sound waves that propagate and eventually reach your ears.

Earthquake waves

Seismic waves are produced by the sudden release of energy in the Earth's crust. Earthquakes generate a combination of transverse (shear or S-waves) and longitudinal (compression or P-waves) mechanical waves.

Example: The sudden shaking of the ground during an earthquake is the result of seismic waves propagating through the Earth's layers.

Light waves

Light waves are a form of electromagnetic waves. They enable us to see and are essential for other processes such as photosynthesis.

Example: Sunlight that reaches Earth is composed of electromagnetic waves that travel through the vacuum of space.

Wave interference

Interference occurs when two or more waves collide with each other. It can be constructive, producing a wave of larger amplitude, or destructive, producing smaller wave amplitudes. This principle is used in various technologies such as noise-canceling headphones.

Example: When two speakers play the same tone, the overlapping sound waves can interfere constructively or destructively to change the intensity of the sound you hear.

Reflection and refraction of waves

Reflection

Reflection occurs when a wave hits an obstacle and bounces back. A common example of this is the echo of a sound wave reflecting off a wall.

Example: Shouting at a canyon wall and hearing your voice come back as an echo.

Refraction

Refraction is the change in the direction of waves as they travel from one medium to another due to a change in speed. The bending of light when passing through a prism or water is a classic example of refraction.

Example: When you put a straw into a glass of water, the waves of light bend as they travel from air into water, making the straw appear bent.

Conclusion

Waves are a fundamental aspect of our experience of the world. Understanding their characteristics and types helps us explain a variety of natural and man-made phenomena. From the sound we hear to the light we see, waves play a vital role in our daily lives. Being armed with the knowledge of waves and their behaviour gives us the tools to explore and innovate in the world of science and technology.


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Waves and their types

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