General Properties of Waves

Wave Features:

  1. Wavefront (front of the wave)
  2. Wavelength (distance between two crests)
  3. Frequency (how often wave crests pass per second)
  4. Crest (highest point)
  5. Trough (lowest point)
  6. Amplitude (height of crest/trough from midline)
  7. Speed (how fast wave moves).

Wave Speed:

  • Determined by the medium (what the wave passes through), not the source.
  • Light always travels at $3.0 \times 10^8\text{ m/s}$ in a vacuum.
  • Formula: (Speed = Frequency $\times$ Wavelength) $$v = f\lambda$$

Types of Waves

Types of Waves

Transverse Waves:

  • Particles vibrate perpendicular to the direction the wave travels.
  • Examples: Light, water ripples, seismic S-waves.

Longitudinal Waves:

  • Particles vibrate in the same direction as wave travel.
  • Examples: Sound, seismic P-waves.

Wave Phenomena

  1. Reflection: Bouncing back off a surface (e.g., echo, mirage). reflection
  2. Refraction: Bending when changing mediums (e.g., straw appearing broken in water). refraction
  3. Diffraction: Bending around obstacles (e.g., spreading through a gap). diffraction

Light

Reflection

Reflection Terms:

  • Normal $\rightarrow$ line perpendicular to mirror
  • Angle of incidence $\rightarrow$ angle between normal and incoming ray
  • Angle of reflection $\rightarrow$ angle between normal and reflected ray.

Plane Mirror: Creates a virtual image that is same size, same distance, but on opposite side. Used in mirrors, telescopes, and periscopes.

Law: Angle of incidence equals angle of reflection. Maintains image sharpness.

Refraction

Light Refraction

Terms:

  • Normal $\rightarrow$ line perpendicular to mirror
  • Angle of incidence $\rightarrow$ angle between normal and incoming ray
  • Angle of reflection $\rightarrow$ angle between normal and reflected ray.

Transparent Blocks: Experiments confirm light changes speed and direction when entering a denser medium (like glass or water).

Critical Angle & Total Internal Reflection

When light hits at or beyond a certain angle in a dense medium, it reflects entirely instead of refracting. Used in optical fibres and diamonds. Total Internal Reflection

Optical Fibres: Use total internal reflection to bounce light through glass cables for long-distance telecommunications.

Thin Lenses

Converging/Diverging Lenses:

  • Convex lenses converge light to form images
  • Concave lenses diverge light. Concave and Convex Lenses

Ray Diagrams: Converging lenses can produce real images (on a screen), enlarged or diminished, and upright or inverted. Ray Diagram

Magnifying Glass & Eyesight Correction: Single lenses used for virtual image formation to enlarge objects or correct refractive errors.

Dispersion

Prism Effect: Glass prism splits white light into a spectrum of 7 colours

  1. Red (Lowest Frequency)
  2. Orange
  3. Yellow
  4. Green
  5. Blue
  6. Indigo
  7. Violet (Highest Frequency)

Monochromatic Light: Light with a single colour/frequency (e.g., a laser).

Image description: Light passing through a glass prism splitting into rainbow colours

Electromagnetic Spectrum

Order:

Radio $\rightarrow$ Microwave $\rightarrow$ Infrared $\rightarrow$ Visible $\rightarrow$ Ultraviolet (UV) $\rightarrow$ X-ray $\rightarrow$ Gamma.

Image description: Electromagnetic spectrum diagram with frequency/wavelength ordering

Properties: All travel at constant speed in vacuum ($3.0 \times 10^8\text{ m/s}$). Higher frequency = shorter wavelength.

Uses:

  • Radio: TV, broadcasting, astronomy, RFID.
  • Microwaves: Satellites, mobile phones, microwave ovens.
  • Infrared: Grills, remotes, thermal imaging, optical fibres.
  • Visible: Vision, photography, illumination.
  • UV: Security marking, fake bank notes, water sterilisation.
  • X-rays: Medical scanning, security scanners.
  • Gamma: Food sterilisation, cancer detection/treatment.

Harmful Effects:

  • Microwaves: Internal heating of food.
  • IR: Skin burns from high intensity.
  • UV: Surface cell damage and skin cancer.
  • X-ray/Gamma: DNA mutation and cellular damage.

Satellite Communication: Low and geostationary orbits use microwaves for broadcasting.

Communication Systems:

  • Mobile/Wireless: Microwaves (penetrate walls, short aerial range).
  • Bluetooth: Radio waves (pass through walls, limited range).
  • Optical Fibres: Visible/IR (glass transparency, very high data rate).

Sound

Production: Sound is produced by vibrating sources (e.g., a guitar string, human vocal cords, or a speaker cone).

Sound Wave

Medium Requirement:

  • Sound cannot travel through a vacuum.
  • It requires matter (air, water, or solids) to travel.
  • Speed varies by medium: Solids ($>5000\text{ m/s}$) $>$ Liquids ($\approx 1500\text{ m/s}$) $>$ Gases ($\approx 330\text{ m/s}$ in air).

Audio Characteristics:

  • Amplitude: Height of the wave. Determines loudness (loud or quiet).
  • Frequency: How many vibrations per second (Hz). Determines pitch (high or low).

Echo: Sound reflecting off a large, smooth surface (e.g., canyon walls, buildings). Used in geology and sonar.

Ultrasound: Sound waves with frequency $> 20\text{ kHz}$ (inaudible to humans).

  • Non-destructive testing: Detects cracks in metals without damage.
  • Medical scanning: Shows internal body structures (pregnancy, bone fractures).
  • Sonar: Underwater navigation and depth measurement. Image description: Ultrasound machine producing sonar waves