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Waves, Sound, and Light

Wave Properties and Oscillations​

1. Characteristics of Waves​

Oscillation (कंपन):

  • Repeated back-and-forth motion
  • Equilibrium position at center
  • Displacement from equilibrium
  • Amplitude: Maximum displacement
  • Period: Time for one complete oscillation
  • Frequency: Number of oscillations per second (Hz)
  • Relationship: f = 1/T

Waves (तरंग):

  • Propagation of oscillation through medium (or space)
  • Carries energy, not matter
  • Particles oscillate but don't travel with wave
  • Wave travels through medium

2. Types of Waves​

Transverse Waves (अनुप्रस्थ तरंग):

  • Oscillation perpendicular to wave direction
  • Crests and troughs (peaks and valleys)
  • Examples: Light, water surface, string vibrations
  • Speed generally higher in denser media

Longitudinal Waves (अनुदैर्ध्य तरंग):

  • Oscillation parallel to wave direction
  • Compressions and rarefactions
  • Examples: Sound in gases, ultrasound
  • Speed depends on medium elasticity

Transverse vs. Longitudinal:

  • Transverse: Perpendicular motion, visible crests/troughs
  • Longitudinal: Parallel motion, pressure variations
  • Both carry energy through medium
  • Different properties in different media

3. Wave Parameters​

Wavelength (तरंगदैर्ध्य) (λ):

  • Distance between adjacent crests (or troughs)
  • Distance between adjacent compressions
  • For transverse: Crest to crest distance
  • For longitudinal: Compression to compression distance
  • Units: Meters (m)

Frequency (f):

  • Number of complete oscillations per second
  • Units: Hertz (Hz) = oscillations per second
  • Higher frequency = more oscillations per second
  • Related to pitch in sound

Speed (v):

  • Distance traveled per unit time
  • Formula: v = fλ
  • Units: m/s
  • Depends on medium properties

Period (T):

  • Time for one complete oscillation
  • Related to frequency: T = 1/f
  • Units: Seconds (s)
  • Longer period = lower frequency

4. Wave Phenomena​

Reflection (परावर्तन):

  • Wave bounces off barrier/surface
  • Angle of incidence = angle of reflection
  • Law of reflection always holds
  • Smooth surfaces: Regular reflection (mirror-like)
  • Rough surfaces: Diffuse reflection (scattered)

Refraction (अपवर्तन):

  • Wave bends when entering different medium
  • Speed changes, frequency stays same
  • Wavelength changes
  • Denser medium: Wave slows, bends toward normal
  • Less dense medium: Wave speeds up, bends away from normal

Diffraction (विवर्तन):

  • Wave bends around obstacle or through slit
  • More pronounced with larger wavelengths
  • Small openings/obstacles cause spreading
  • Long wavelength waves diffract more
  • Uses: Ultrasound, radar, astronomy

Standing Waves (स्थिर तरंग):

  • Formed when waves reflect and interfere
  • Nodes: Points of zero displacement
  • Antinodes: Points of maximum displacement
  • Example: Vibrating strings, resonance in pipes

Sound Waves​

1. Properties of Sound​

Sound Characteristics:

  • Longitudinal wave (in all media: solid, liquid, gas)
  • Requires medium to propagate
  • Cannot travel in vacuum
  • Speed in air: ~343 m/s at 20°C
  • Speed increases with temperature

Speed in Different Media:

  • Air: ~343 m/s
  • Water: ~1,480 m/s
  • Steel: ~5,000 m/s
  • General: Faster in denser media
  • Exceptions: Gases with different properties

2. Frequency and Pitch​

Audible Range (श्रव्य):

  • Human hearing: 20 Hz to 20,000 Hz
  • Infrasound: Below 20 Hz
  • Ultrasound: Above 20,000 Hz

Pitch:

  • Perception of frequency
  • Higher frequency = higher pitch
  • Lower frequency = lower pitch
  • Frequency directly determines pitch

Intensity (तीव्रता):

  • Power per unit area
  • Related to amplitude
  • Units: W/m² or dB (decibels)
  • Louder sound = greater intensity
  • Logarithmic scale (decibels)

Loudness:

  • Perception of intensity
  • Depends on frequency
  • Human ear more sensitive to certain frequencies
  • Measured in decibels (dB)

3. Sound Applications​

Ultrasound:

  • Sound above human hearing range (>20 kHz)
  • Medical imaging: Ultrasound scans (pregnancy, organs)
  • Cleaning: High-frequency vibrations
  • Pest control: Repels animals
  • Sonar: Detection in water

Doppler Effect:

  • Frequency changes as sound source moves
  • Approaching: Frequency increases (higher pitch)
  • Receding: Frequency decreases (lower pitch)
  • Perceived change in frequency/pitch
  • Applications: Radar, astronomy, medical (blood flow)

4. Resonance​

Resonance (अनुनाद):

  • Vibration at natural frequency
  • Large amplitude oscillations
  • Driving frequency matches natural frequency
  • Energy efficiently transferred
  • Example: Vibrating tuning fork causes resonance in another

Resonance Frequency:

  • Each object has natural frequency
  • Depends on size, shape, material
  • Small object: Higher frequency
  • Larger object: Lower frequency

Light and Electromagnetic Waves​

1. Electromagnetic Spectrum (विद्युत चुंबकीय स्पेक्ट्रम)​

Properties of EM Waves:

  • Transverse waves
  • Do not require medium
  • Travel at speed of light (3 × 10⁸ m/s in vacuum)
  • All electromagnetic waves related by c = fλ

Types (from long to short wavelength):

  1. Radio waves: Longest wavelength, lowest frequency

    • Broadcasting, communication, radar

  2. Microwaves: Short radio waves

    • Cooking, communication, heat transfer

  3. Infrared: Heat radiation

    • Thermal imaging, cooking, sun's heat

  4. Visible Light: Only EM waves humans see

    • Red → Orange → Yellow → Green → Blue → Indigo → Violet
    • Shorter wavelength = higher frequency = more energy

  5. Ultraviolet: Beyond violet light

    • Tanning, sterilization, fluorescence

  6. X-rays: High energy, penetrating

    • Medical imaging (bones), security

  7. Gamma rays: Highest frequency, most energetic

    • Radioactive decay, cancer treatment

2. Light Properties​

Speed of Light:

  • c = 3 × 10⁸ m/s in vacuum
  • Slower in denser media (glass: 2 × 10⁸ m/s)
  • Different wavelengths travel same speed in vacuum
  • Different speeds in media (dispersion)

Index of Refraction:

  • n = c/v (speed of light / speed in medium)
  • Higher n = more dense optically
  • Greater bending at interfaces
  • Glass: n ≈ 1.5
  • Air: n ≈ 1.0

Dispersion:

  • Different wavelengths refract differently
  • Different refractive indices for different colors
  • Violet bends more than red
  • Creates spectrum (prism, rainbow)

3. Lenses and Optical Instruments​

Converging Lens (उत्तल लेंस):

  • Thicker in center, thinner at edges
  • Brings parallel rays to focus
  • Real images (can be projected)
  • Used in cameras, magnifying glasses, microscopes

Diverging Lens (अवतल लेंस):

  • Thinner in center, thicker at edges
  • Spreads parallel rays
  • Virtual images (cannot project)
  • Used in corrections for myopia

Lens Equation:

  • 1/f = 1/u + 1/v
  • f = focal length
  • u = object distance
  • v = image distance
  • Magnification: m = v/u

Optical Instruments:

  • Camera: Converging lens, real inverted image on film
  • Microscope: Two converging lenses, very high magnification
  • Telescope: Converging objective, eyepiece, distant objects
  • Eye: Cornea and lens focus light, retina detects image

4. Color​

Visible Spectrum:

  • Wavelength range: 400-700 nm
  • Red: ~700 nm (lowest frequency visible)
  • Violet: ~400 nm (highest frequency visible)
  • Different wavelengths perceived as different colors

Color Mixing:

  • Additive (light): Red + Green + Blue = White

    • Mixing lights (displays, spotlights)

  • Subtractive (pigment): Cyan + Magenta + Yellow = Black

    • Mixing paints (printing, art)

Color Properties:

  • Hue: Type of color (determined by wavelength)
  • Saturation: Purity of color (amount of white mixed in)
  • Brightness: Intensity of light

Applications of Waves​

1. Communication​

Radio and Microwave:

  • Long-distance communication
  • Radio: Lower frequency, longer range
  • Microwave: Higher frequency, shorter range
  • Modulation carries information

Fiber Optics:

  • Uses light in optical fibers
  • Total internal reflection keeps light inside
  • Long distance, high bandwidth
  • Perfect for internet and telecommunications

2. Medical Applications​

X-rays:

  • Penetrate soft tissue, absorbed by bone
  • Create images of internal structures
  • High doses cause damage (use carefully)

Ultrasound:

  • Sound waves create echoes
  • Noninvasive imaging
  • No known harm for diagnostic use
  • Useful for pregnancy and organs

Thermal Imaging:

  • Detects infrared radiation
  • Shows temperature variations
  • Medical diagnostics, rescue, security

3. Astronomical Applications​

Telescopes:

  • Optical telescopes use lenses/mirrors
  • Radio telescopes detect radio waves from space
  • Different wavelengths reveal different features

Spectroscopy:

  • Analyze light from stars
  • Determine composition, temperature, motion
  • Different elements emit different wavelengths

Summary​

Waves and light explain:

  • Wave Properties: Oscillation, propagation, parameters
  • Sound: Longitudinal waves, frequency, applications
  • Light: Electromagnetic wave, spectrum, visual perception
  • Optical Instruments: Lenses, microscopes, telescopes
  • Applications: Communication, medicine, astronomy

Understanding waves fundamental to modern technology from radio to X-rays to fiber optics.