Grade 10
  1. Mechanics  1.1. Dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. Displacement and Distance  1.1.4. Speed and Velocity  1.1.5. Acceleration  1.1.6. Graphical representation of motion  1.1.7. Equations of motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Projectile motion  1.1.10. Relative speed  1.2. Dynamics  1.2.1. Newton's Laws of Motion  1.2.2. Inertia and mass  1.2.3. Force and its types  1.2.4. action and reaction force  1.2.5. Friction and its effects  1.2.6. Coefficient of friction  1.2.7. Circular motion  1.2.8. Centripetal force and centripetal acceleration  1.2.9. Momentum and Impulse  1.2.10. Conservation of momentum  1.2.11. Newton's third law and applications  1.3. Work, Energy and Power  1.3.1. Work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy  1.3.5. Mechanical energy  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.3.8. Renewable and non-renewable energy sources  1.4. Gravitational force  1.4.1. Newton's law of universal gravitation  1.4.2. Gravitational field and field strength  1.4.3. Acceleration due to gravity on different planets  1.4.4. Kepler's laws of planetary motion  1.4.5. Orbits and satellites  1.4.6. Weight and apparent weight  1.4.7. Gravitational potential energy
  2. Properties of matter  2.1. States of matter  2.1.1. Solid, liquid and gas  2.1.2. Molecular structure of matter  2.1.3. Intermolecular forces  2.1.4. Plasma and Bose–Einstein condensate  2.2. Pressure  2.2.1. Definition of Pressure  2.2.2. Pressure in liquids  2.2.3. Atmospheric pressure  2.2.4. Pascal's principle  2.2.5. Archimedes' Principle and Buoyancy  2.2.6. Surface tension and capillarity  2.3. Elasticity  2.3.1. Hooke's law  2.3.2. Stress and strain  2.3.3. Elastic Limit and Modulus of Elasticity  2.3.4. Applications of Elasticity
  3. Thermal physics  3.1. heat and temperature  3.1.1. Difference Between Heat and Temperature  3.1.2. Temperature scale  3.1.3. Thermal expansion  3.1.4. Thermal equilibrium  3.2. Heat transfer  3.2.1. Conductivity  3.2.2. Convection  3.2.3. Radiation  3.2.4. Insulation and its applications  3.3. Thermal properties of matter  3.3.1. Specific heat capacity  3.3.2. Latent heat and phase change  3.3.3. Boiling and Melting Point  3.3.4. Heat engines and refrigeration  3.4. Laws of Thermodynamics  3.4.1. Zeroth law of thermodynamics  3.4.2. First law of thermodynamics  3.4.3. Second law of thermodynamics  3.4.4. Carnot cycle
  4. Waves and optics  4.1. Nature and properties of waves  4.1.1. Types of waves in nature and properties of waves  4.1.2. Transverse and longitudinal waves  4.1.3. Wave parameters  4.1.4. Reflection and refraction of waves  4.1.5. Superposition and Interference  4.1.6. Standing Waves and Resonance  4.1.7. Doppler effect  4.2. Sound waves  4.2.1. Characteristics of sound waves  4.2.2. Speed of sound in different mediums  4.2.3. Applications of sound waves  4.2.4. Ultrasound and its uses  4.3. Light Waves and Optics  4.3.1. Nature of light  4.3.2. Reflection of light  4.3.3. Laws of reflection  4.3.4. Mirrors and Image Formation  4.3.5. Refraction of light  4.3.6. Snell's Law  4.3.7. Lenses and Image Formation  4.3.8. Total internal reflection and critical angle  4.3.9. Optical fibre  4.4. Optical Instruments  4.4.1. Microscope  4.4.2. Telescope  4.4.3. Human eye and vision defects  4.4.4. Camera and its working principle
  5. Electricity and Magnetism  5.1. Electrostatics  5.1.1. Electric charge and its properties  5.1.2. Conductors and Insulators  5.1.3. Coulomb's law  5.1.4. Electric field and field lines  5.1.5. Electric potential and potential difference  5.1.6. Capacitors and Capacitance  5.2. Current Electricity  5.2.1. Electric current and its measurement  5.2.2. Ohm's law  5.2.3. Resistance and resistivity  5.2.4. Series and Parallel Circuits  5.2.5. Electric power and energy  5.2.6. Kirchhoff's Laws  5.3. Magnetism and Electromagnetism  5.3.1. Magnetic field and field lines  5.3.2. Magnetic effects of electric current  5.3.3. Electromagnetic induction  5.3.4. Faraday's laws of electromagnetic induction  5.3.5. Transformers and Applications  5.3.6. AC and DC current
  6. Modern Physics  6.1. Nuclear physics  6.1.1. Structure of the atom  6.1.2. Bohr's atomic model  6.1.3. Electron Energy Levels  6.1.4. X-rays and applications  6.2. Radioactivity  6.2.1. Types of radiation  6.2.2. Half-life and radioactive decay  6.2.3. Nuclear reactions and applications  6.2.4. Fission and Fusion  6.3. Quantum physics  6.3.1. Wave–particle duality  6.3.2. Photoelectric effect  6.3.3. Energy quantization  6.3.4. Heisenberg's uncertainty principle
  7. Electronics and Communication  7.1. Semiconductors  7.1.1. Conductors, Insulators and Semiconductors  7.1.2. Diodes and their applications  7.1.3. Transistors and Logic Gates  7.1.4. LEDs and photodiodes  7.2. Communication Systems  7.2.1. Basics of communication  7.2.2. Analog and digital signals  7.2.3. Wireless and optical fibre communication  7.2.4. Radio Waves and Modulation

Grade 10 → Waves and optics → Nature and properties of waves ↓


Doppler effect


The Doppler effect is a fascinating phenomenon that occurs when a source of waves such as sound or light is moving relative to an observer. This effect is evident in a variety of fields, from everyday phenomena to more complex scientific observations. By exploring the principles behind the Doppler effect, we can better understand the complex nature of waves and their interaction with the world around us. Let's understand this in a simple and comprehensive way.

Understanding waves

Before delving deeper into the Doppler effect, it is important to understand the basic nature of waves. Waves are disturbances or oscillations that travel through space and matter, transferring energy from one point to another. Common types of waves include sound waves, light waves, and water waves.

Types of waves

  • Sound waves: These are longitudinal waves that travel through a medium such as air, water or solids. Sound waves need a medium to travel.
  • Light waves: These are transverse waves that can travel in the vacuum of space. Light waves do not require any medium.
  • Water waves: These are also transverse waves that move on the surface of water bodies.

What is the Doppler effect?

The Doppler effect, named after Christian Doppler, who first proposed it in 1842, describes the change in the frequency or wavelength of a wave when the source of the wave is moving relative to the observer. If the source of the waves is moving toward the observer, the waves are compressed, resulting in a shift to higher frequency or toward the blue end of the spectrum in the case of light. Conversely, if the source is moving away, the waves are stretched, leading to a shift to lower frequency or toward the red end of the spectrum.

An everyday example: a passing ambulance

Imagine you are standing on the sidewalk and an ambulance is approaching you with its siren blaring. As the ambulance approaches you, the sound waves are compressed and you hear a higher pitched sound. As the ambulance passes and moves away, the sound waves are stretched and the sound becomes lower. This change in sound is a clear demonstration of the Doppler effect.

Illustration of the effect

Consider this simple example of sound wave compression and stretching:

Source near:, Compressional waves (high frequency) The source is moving away:, Dispersed waves (low frequency)

Explained with physics: Doppler effect formula

The mathematical representation of the Doppler effect is important for measuring this phenomenon. The general formula for calculating the observed frequency ( f' ) is:

f' = f * (v + v_o) / (v + v_s)

Where:

  • f' is the observed frequency.
  • f is the emitted frequency of the source.
  • v is the velocity of the waves in the medium.
  • v_o is the velocity of the observer (positive if moving towards the source).
  • v_s is the velocity of the source (positive if moving away from the observer).

The formula shows the relationship between the observed frequency and the velocities involved. Understanding it can help predict how different conditions affect the frequency perceived by the listener.

A practical example: the train whistle

Suppose a train is moving toward a stationary observer blowing a whistle at a frequency of 500 Hz. The speed of sound in air is about 343 m/s, and the train is moving at a speed of 30 m/s. To find the frequency of the sound heard by the observer, we can use the formula:

f' = 500 * (343 + 0) / (343 - 30) = 545.7 Hz

Therefore, the observer hears the train whistle at a frequency of 545.7 Hz, which is higher than the original 500 Hz. This increase in frequency occurs because the train is moving towards the observer.

Light and the Doppler effect

While the Doppler effect is most commonly associated with sound waves, it also affects electromagnetic waves, including light. In astronomy, this phenomenon is important for understanding the motion and velocity of celestial objects.

Redshift and blueshift

In the context of light, the Doppler effect causes phenomena called "redshift" and "blueshift" by astronomers.

  • Redshift: When a light source moves away from an observer, the light waves stretch out, increasing their wavelength and shifting them toward the red end of the spectrum.
  • Blueshift: When a light source moves closer, the light waves are compressed, which reduces their wavelength and shifts them towards the blue end of the spectrum.

These variations are important in determining the speed and distance of stars and galaxies. Observations of redshift in distant galaxies have been important in establishing that the universe is expanding.

Simple representation of light waves

Think of these representations as keys to understanding how light behaves with speed:

Source near:, Compression waves (short wavelength) The source is moving away:, Dispersed waves (longer wavelength)

Applications of Doppler effect

The Doppler effect is not just an academic curiosity; it has practical applications in many fields. Here are some notable applications:

  • Radar and sonar: Radar systems use the Doppler effect to determine the speed of a moving object by bouncing radio waves off them and measuring the frequency changes. Similarly, sonar systems use sound waves underwater.
  • Astronomy: Astronomers use the Doppler effect to measure the speed of stars and galaxies, and determine whether they are moving toward us or away from us.
  • Medical imaging: In medicine, Doppler ultrasound is used to look at blood flow in the vessels, helping to diagnose cardiac problems.

Working with radar

To illustrate how radars work using the Doppler effect, consider a police radar gun aimed at an oncoming vehicle. The radar emits a signal that bounces off the car and bounces back. The frequency change in the returned signal indicates the vehicle's speed. The same principle applies to weather radar that tracks precipitation and storm velocity.

Conclusion

The Doppler effect reveals the dynamic nature of waves and their interaction with moving sources and observers. Whether we are interpreting the siren of an emergency vehicle, studying the light coming from distant stars, or using advanced radar and medical techniques, understanding the Doppler effect opens windows to exploring and explaining the universe.

By appreciating the simplicity and importance of this concept, students and curious minds can gain a deeper understanding of waves and the motion inherent in the physical world.


Grade 10 → 4.1.7


U
username
0%
completed in Grade 10

← Prev (4.1.6)
Standing Waves and Resonance
Next (4.2) →
Sound waves

Comments 



Doppler effect

https://www.physicsflow.com/g10/4.1.7?pfal=en