Waves and Wave Properties

Vocabulary

  • Wavelength: The distance between two consecutive crests or troughs of a wave. Denoted by the symbol λ\lambda (lambda).

  • Amplitude: The maximum distance a wave moves from its rest/mean position; it determines the loudness of the wave.

  • Frequency: The number of waves passing a specific point per second, measured in Hertz (Hz).

  • Crest: The highest point of a wave.

  • Trough: The lowest point of a wave.

  • Mean Position: The rest position where the wave would be if there were no disturbances.

  • Pitch: The perceived frequency of a sound.

Wave Behavior

  • Reflection: The bouncing of a wave off a surface. Laws of reflection state:

    1. The angle of incidence is equal to the angle of reflection.

    2. The incident ray and reflected ray lie in the same plane with respect to the normal.

  • Refraction: The bending of a wave when it passes from one medium to another. It is defined by the refractive index nn, where:
    n=speed of light in vacuumspeed of light in mediumn = \frac{\text{speed of light in vacuum}}{\text{speed of light in medium}}

    • Air: n=1n = 1

    • Water: n=1.33n = 1.33

    • Glass: n=1.5n = 1.5

    • Diamond: n=2.45n = 2.45

Types of Waves

  • Transverse Waves: Waves where the medium moves at right angles to the direction of wave propagation (e.g. electromagnetic waves, light).

  • Longitudinal Waves: Waves where the medium moves parallel to the wave direction (e.g. sound waves). They require a medium for propagation.

Wave Speed Equation

  • The speed of a wave is calculated using the formula:
    v=f×λv = f \times \lambda

    • Where vv is wave speed, ff is frequency, and λ\lambda is wavelength.

  • The speed of light in a vacuum is approximately 3×108 m/s3 \times 10^8 \text{ m/s}. The speed of sound is approximately 340 m/s340 \text{ m/s} at 20°C.

Frequency and Time Period

  • Frequency: Number of waves passing a point in one second (measured in Hz).

  • Time Period (T): The time taken to complete one oscillation (1 complete wave). Relationship with frequency:
    f=1Tf = \frac{1}{T}

Diffraction and Infrasonic/Ultrasonic Sound

  • Diffraction: The spreading of waves when they encounter an obstacle or pass through a narrow opening.

  • Infrasonic Sound: Sounds with frequencies less than 20 Hz.

  • Audible Range for Humans: 20 Hz to 20,000 Hz.

  • Ultrasonic Sound: Sounds with frequencies greater than 20,000 Hz.