Unit 3 Lecture Notes: Waves

Overview & Structure

• Unit 3 is divided into two parts:
  • Part 1: General properties of waves
  • Part 2: Specific focus on light

Checklist Reminder

• At the beginning of each chapter, use the provided checklist to verify understanding.
• Example formula to know: ( V = f \lambda )

General Properties of Waves

Definition of a Wave

• A wave is the transfer of energy without transferring matter.
  • Molecules vibrate but do not move with the wave.

Types of Waves

1. Mechanical vs Electromagnetic:
   • Mechanical: Requires a medium (e.g., sound waves)
   • Electromagnetic: Does not require a medium (e.g., light waves)
2. Transverse vs Longitudinal:
   • Transverse: Particles vibrate perpendicular to wave direction; includes electromagnetic waves.
   • Longitudinal: Particles vibrate parallel; includes sound waves.

Seismic Waves

• P-wave (Primary/Pressure wave): Longitudinal, travels underground, fast.
• S-wave (Secondary/Surface wave): Transverse, vibrates up and down, slower.

Wave Properties

• Wavefront: Lines perpendicular to wave rays, representing crests or compressions.
• Amplitude: Maximum displacement from mean position, indicates wave energy.
• Wavelength: Distance between successive crests/troughs; distance for one complete oscillation.
• Period: Time for one oscillation.
• Frequency: Number of oscillations per second (measured in Hertz).
• Wave Speed: Calculated as ( v = f \lambda ).

Wave Behaviors

1. Reflection

   • Change in direction when a wave hits a surface.
   • Law: Angle of incidence = angle of reflection.

2. Refraction

   • Change in wave speed due to a change in medium.
   • From less dense to more dense: Speed and wavelength decrease, wave bends towards the normal.
   • From more dense to less dense: Speed and wavelength increase, wave bends away from the normal.

3. Diffraction

   • Spreading of a wave as it passes through a gap or around an edge.
   • Larger gap relative to wavelength: Less spreading.
   • Smaller gap: More spreading.

Sound Waves

• Type: Mechanical longitudinal waves.
• Speed: Varies with medium (Air: 330 m/s, Water: 1500 m/s, Steel: 5000 m/s).
• Amplitude: Affects loudness.
• Frequency: Affects pitch.
• Human Hearing: 20 Hz to 20,000 Hz.
• Applications: Sonar, medical imaging, non-destructive testing.
• Echoes: Reflection of sound, time measured for sound to travel to and back from a surface.

Electromagnetic Spectrum

• Common Properties:
  • Travel through vacuum
  • Speed in vacuum: (3 \times 10^8) m/s
  • All are transverse waves.
• Order: Radio waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma rays.
• Uses:
  • Radio: Communication, Bluetooth
  • Microwaves: Satellite communication, mobile phones
  • Infrared: Heating, remote controls
  • Visible Light: Vision, photography
  • Ultraviolet: Sterilization
  • X-rays: Medical imaging
  • Gamma rays: Sterilization, cancer treatment

Digital vs Analog Signals

• Digital: High or low values, efficient and less noise.
• Analog: Continuous range, natural signals.

Summary

• Understanding wave properties and behaviors is crucial for analyzing sound and electromagnetic waves.
• Application in technology and medical fields highlights the importance of mastering these concepts.