chapter 19-20

Chapter 19 -

  • Vibration: Periodic wiggle in time.

  • Wave: Periodic wiggle in space and time; extends from one place to another.

  • Pendulum's Period: Depends only on its length, not mass.

  • Wave Characteristics:

    • Crests: High points.

    • Troughs: Low points.

    • Amplitude: Distance from midpoint to crest or trough.

    • Wavelength: Distance between crests.

  • Frequency (f): Number of vibrations per unit time; unit: Hertz (Hz).

  • Period (T): Time to complete one vibration; related to frequency: T=1fT = \frac{1}{f}.

  • Wave Speed (v): How fast a disturbance moves through a medium; v=f×λv = f \times \lambda (where ( \lambda ) is wavelength).

Wave Types

  • Transverse Wave: Medium vibrates perpendicularly to energy transfer.

  • Longitudinal Wave: Medium vibrates parallel to energy transfer; includes compressions and rarefactions.

Wave Interference

  • Occurs when waves interact in the same place at the same time.

  • Superposition Principle: Displacement from interference is the sum of individual disturbances.

  • Constructive & Destructive Interference.

  • Standing Waves:

    • Nodes: Minimal displacement & energy.

    • Antinodes: Maximum displacement & energy.

The Doppler Effect

  • Blue Shift: Increase in frequency if source approaches.

  • Red Shift: Decrease in frequency if source moves away.

Chapter 20 - Sound

  • Sound: Produced by vibrations of matter (e.g., instruments, voice).

  • Pitch: Subjective impression of frequency; normal hearing range: 20 Hz - 20,000 Hz.

  • Frequencies:

    • Infrasonic: Below 20 Hz (too low for human hearing).

    • Ultrasonic: Above 20,000 Hz (too high for human hearing).

  • Sound Waves: Longitudinal waves, can travel through solids, liquids, gases.

  • Speed of Sound:

    • Faster in water (4x), even faster in steel (15x).

    • Conditions affecting speed: temperature, humidity, wind.

    • Speed in air at 0°C is about 330 m/s; increases by 0.6 m/s per °C.

Reflection & Refraction

  • Reflection: Sound returns upon encountering a surface; can create echoes and reverberations.

  • Refraction: Bending of waves due to speed changes caused by wind and temperature variations.

Ultrasound

  • Device using high-frequency sounds to create images of internal organs.

Resonance & Interference

  • Natural Frequency: Unique frequency of an object, determined by elasticity and shape.

  • Resonance: Occurs when forced vibrations match an object's natural frequency.

  • Beats: Variations in loudness due to interference, providing frequency comparisons.