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 ↓


Wavelength, frequency and speed of the wave


Waves are one of the fundamental phenomena in the universe. They are found in various forms, such as sound waves, water waves, and electromagnetic waves like light. To understand waves, it is important to know some key concepts: wavelength, frequency, and wave speed. In this lesson, we will explore these concepts in detail.

What is a wave?

A wave is a disturbance that travels through a medium, transferring energy from one point to another without moving matter. This means that the particles of the medium vibrate around their rest positions without net motion in the direction of travel of the wave.

Types of waves

Waves may be broadly classified into two main types:

  • Mechanical waves: These need a medium to travel, such as air, water, or a solid. Examples include sound waves and water waves.
  • Electromagnetic waves: These do not require a medium and can travel in the vacuum of space. Light waves, radio waves, and X-rays are examples.

Wavelength

The wavelength of a wave is the distance between successive points on the wave that are in the same phase — for example, the distance between two successive crests or troughs. Wavelength is usually represented by the Greek letter lambda (λ) and is measured in meters (m).

Visual example:

Wavelength (λ)

In the figure above, the wavelength is the distance between the two dotted lines, extending from one peak to the other.

Frequency

The frequency of a wave indicates how many waves pass a point in one second. It is a measure of how many times the particles in a medium vibrate when a wave passes through them. The unit of frequency is Hertz (Hz), where 1 Hertz equals 1 cycle per second. Frequency is represented by the symbol f.

Text example:

If the frequency of a wave is 5 Hz, it means that 5 wave peaks pass a certain point every second.

Wave speed

The speed of a wave is the speed that the wave is traveling through the medium. It is the distance that the wave travels per unit of time. The speed of a wave is often represented by the letter v and its unit is meters per second (m/s).

Formula of wave speed:

The relationship between wavelength, frequency and speed of a wave is given by the following equation:

v = f * λ

Where:

  • v is the speed of the wave (meter/second)
  • The frequency of the f wave is (Hz)
  • λ is the wavelength of the wave (meters)

Example calculation:

Suppose the wavelength of a wave is 2 m and frequency is 4 Hz, then its speed can be calculated as follows:

v = 4 Hz * 2 m = 8 m/s

Relation between wavelength, frequency and energy

It is important to note that frequency and wavelength are inversely related. This means that if the frequency increases, the wavelength decreases, and vice versa, while the speed of the wave in a given medium remains constant. Additionally, in electromagnetic waves, higher frequencies correspond to higher energy.

Visual example:

Consider a ripple in a pond:

Crest Compact peak

In the diagram, consider two different waves in the pond. The blue wave has peaks more spaced apart, indicating lower frequency and longer wavelength. The red wave has peaks more closely spaced, indicating higher frequency and shorter wavelength.

Real-life applications

  • Understanding how waves work is important in designing efficient communications systems, where the frequency determines the type of wave used (e.g., radio waves, microwaves).
  • In medicine, ultrasound technology relies on high-frequency sound waves to create images of organs within the body.
  • Seismologists study earthquake waves to understand the Earth's internal structure.

Conclusion

Wavelength, frequency and speed are essential properties of waves that determine their behaviour in various contexts. A clear understanding of these concepts enables us to apply them in various scientific and practical fields, from designing musical instruments to exploring the universe through electromagnetic waves.


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Properties of Waves
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Wavelength, frequency and speed of the wave

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