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 → Sound waves ↓


Sonar and ultrasound


Sound waves are a fascinating part of physics, and they have many applications in our daily lives, from helping us hear music to allowing communication between people. The many interesting uses of sound waves include technologies such as sonar and ultrasound. In this article, we will explore these technologies in detail, discussing how they work and what their applications are in different fields.

Understanding sound waves

Sound waves are vibrations that travel through the air (or another medium) and can be heard when they reach the ear of a person or animal. Here's how they work at a basic level:

  • Sound is a type of energy that is produced by vibrating objects. The vibrations of these objects cause the air molecules around them to move.
  • These molecules collide with each other, creating a wave of pressure changes in the air, which our ears sense.
  • When these pressure changes reach our ears, they cause our eardrums to vibrate, which our brain interprets as sound.

What is sonar?

Sonar stands for Sound Navigation and Ranging. It is a technology that uses sound waves to "see" underwater. It works by emitting sound waves and listening for the echoes as they bounce off objects. Here is how sonar works in steps:

  1. Sonar instrument emits sound waves in the form of short pulses.
  2. This sound wave travels through the water and strikes an object, such as a fish or the sea floor.
  3. The sound wave returns back as an echo.
  4. The sonar instrument receives the echo and measures the time it takes for it to return.
  5. Using the speed of sound in water (about 1482 m/s), the device calculates the distance to the object.

Sonar types

There are two main types of sonar: active sonar and passive sonar.

Active sonar

  • Active sonar sends out a sound pulse or ping and then listens for the echo.
  • It's like sitting in a cave and screaming and waiting to hear the echo of your voice.
  • This type of sonar is commonly used for navigation and fish finding.
  • Applications: Submarines use it to detect underwater objects; ships use it to find fish.

Passive sonar

  • Passive sonar does not send out sound waves, but only listens to sound waves coming from other ships or marine animals.
  • It's just listening, just like eavesdropping on a conversation.
  • This type of sonar is often used in military applications to detect enemy submarines by listening for the sound of their engines.

Sonar applications

Sonar has many applications in both civilian and military contexts:

  • Navigation: Ships use sonar to navigate safely, especially in murky waters or at night.
  • Fishing: Fishermen use sonar to locate schools of fish, making fishing more efficient.
  • Military: Sonar is used in submarines and warships to detect enemy submarines and landmines.
  • Scientific research: Researchers use sonar to map the ocean floor and study marine life.

Understanding ultrasound

Ultrasound refers to sound waves that have a frequency higher than the upper audible limit of human hearing, which is about 20,000 Hertz (Hz). Humans cannot hear ultrasound, but it is extremely useful in a variety of applications, especially in medicine.

How ultrasound works

Ultrasound works in a similar way to SONAR, but it is typically used in a different context and with much higher frequencies. Here is a basic outline of how ultrasound works:

  1. The ultrasound machine sends high frequency sound waves into the body.
  2. These sound waves travel through the body's tissues and are reflected when they hit boundaries between different types of tissue (such as fluid and soft tissue, or tissue and bone).
  3. The machine picks up these echoes and uses them to make a picture, called an ultrasound image.
  4. By analyzing these echoes, doctors can examine internal organs, blood flow, and other structures inside the body.

Applications of ultrasound

Ultrasound has many applications beyond medical imaging; however, its most well-known uses are in medicine:

Medical imaging

  • Pregnancy: Ultrasound is commonly used to check the development of a baby inside a woman's womb.
  • Diagnosis: Doctors use ultrasound to diagnose a variety of conditions in organs such as the liver, kidneys, heart, and bladder.
  • Guidance for procedures: Ultrasound can help guide surgeons during certain procedures, such as biopsies.

Non-medical use

  • Cleaning: Ultrasound is used to clean delicate objects, such as jewelry and surgical instruments.
  • Industrial testing: Ultrasound is used to detect cracks in metal structures, such as airplane wings, without damaging them.
  • Pest control: Some devices use ultrasound to ward off pests such as mice and insects.

Comparison of sonar and ultrasound

Similarities

  • Both use sound waves to detect objects or create images.
  • Both depend on the principles of sound wave reflection and resonance.

Contraindications

Sonar Ultrasound
Typically used in aquatic environments. Mainly used in medical and industrial settings.
Operates in the low frequency range. Operates in the high frequency range.
Uses water as the medium for sound waves. Uses the body or air as the medium for sound waves.
Typically used for navigation and exploration. Typically used for imaging and treatment.

The principles of physics behind sonar and ultrasound

Both sonar and ultrasound rely on the basic principle of sound wave reflection to work:

Reflection of sound waves

Reflection occurs when sound waves bounce back after hitting a surface. This is why when you shout in a large empty room, you may hear an echo. This echo is the sound wave reflecting off the walls and coming back to your ears.

Speed of sound

The speed of sound varies in different mediums, which affects the way sonar and ultrasound work. For example:

  • The speed of sound in air at room temperature is about 343 meters per second.
  • The speed of sound in water is high, about 1482 meters per second, which is why sonar is effective in aquatic environments.
  • In the human body, sound travels at different speeds depending on the type of tissue; for example, it travels at about 1540 meters per second in soft tissues.

Frequency and wavelength

Frequency refers to the number of wave cycles passing a point per second. It is measured in Hertz (Hz). Wavelength is the distance between two consecutive points of a wave in one phase, such as the distance between two crests. The relationship between these can be defined by the formula:

Velocity = frequency × wavelength

For ultrasound, the sound waves have a very high frequency and short wavelength, allowing them to create detailed images of small objects. In comparison, sonar waves have a very low frequency and long wavelength, making them suitable for detecting larger objects at greater distances.

Visual examples of sound waves

It may help to understand how sound waves, sonar, and ultrasound work. Below are simple diagrams that show how each works.

Sonar Pulse Echo

In this example, a SONAR instrument sends out a pulse, which bounces off an object and returns as an echo.

Inside the body Ultrasound image

This illustration shows an ultrasound wave entering the body and creating an image on a monitor using the reflected waves.

Conclusion

In conclusion, both sonar and ultrasound are important technologies that harness the power of sound waves for specific purposes. While sonar aids in navigation, mapping, and exploration, ultrasound plays a vital role in medical diagnosis and treatment. Understanding these technologies through the lens of sound physics not only highlights their simplicity but also underlines the essential role of sound waves in many scientific and practical applications.


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Sonar and ultrasound

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