Physical science 6

Wave Motion Characteristics

  • Waves transfer energy without transferring matter.

  • - Water Waves: Move matter up and down without lateral movement.

    • Earthquake Waves: Travel through solid materials.

    • Sound Waves: Require a gaseous medium (typically air).

    • Electromagnetic Waves: Propagate through a vacuum (void).

Wave Properties

  • A disturbance can be classified as:- Single Pulse or Shock: Example - hammer hitting a surface.

    • Periodic: Example - vibrations of a guitar string.

Classification of Waves

  • Transverse Waves:- Particle motion is perpendicular to wave direction.

    • Example: Light waves.

  • Longitudinal Waves:- Particle motion is parallel to wave direction.

    • Example: Sound waves.

Key Wave Metrics

  • Wavelength ( ): Distance of one complete wave cycle.

  • Amplitude: Maximum displacement from equilibrium. - Energy transported is proportional to the square of the amplitude.

Wave Characterization

  • Frequency (f): Number of cycles per second (Hz).

  • Period (T): Time for one wavelength to pass a point.

  • Speed of Wave (v):- Formula: v=lTv = \frac{l}{T} or v=lfv = lf .

    • Variables:

    • vv = wave speed (m/s)

    • ll = wavelength

    • TT = period (s)

    • ff = frequency (Hz)

Electromagnetic Spectrum and Interactions

  • The electromagnetic spectrum ranges from longest wavelength (lowest frequency) to shortest wavelength (highest frequency):

    • Radio waves: Longest wavelength, lowest frequency. Cause molecule vibration.

    • Microwaves: Cause molecule rotation.

    • Infrared: Cause stretching and bending of bonds.

    • Visible light: Causes electron excitation.

    • UV/X-ray: Cause bond breaking.

    • Gamma rays: Shortest wavelength, highest frequency. Cause atom disintegration.

Sound Waves Overview

  • Sound: Longitudinal waves propagating through matter (solid, liquid, gas).

  • Tuning Fork Example:- Vibration produces compressions (high pressure) and rarefactions (low pressure).

Sound Spectrum

  • Sound waves are divided into regions:

  • Infrasonic: f < 20 \text{ Hz}

  • Audible: 20 \text{ Hz} < f < 20 \text{ kHz}

  • Ultrasonic: f > 20 \text{ kHz}

Loudness and Intensity

  • Loudness: Relative term; intensity is quantitative measure of energy transfer rate.

    • Pain threshold: approximately 1 W/m².

    Intensity: A measure of the rate of energy transfer through a given area

Decibel Scale

  • Decibels (dB): Measurement unit for sound intensity; logarithmic scale.- 1 Bel (B) = 10 dB.

    • Not a linear scale; doubling sound intensity increases dB by only 3 dB.

Doppler Effect

  • Change in frequency due to relative motion of source and observer.- Approaching source: waves bunched, higher frequency.

    • Departing source: waves spread, lower frequency.

Applications of the Doppler Effect

  • Blue shift: Light sources approaching.

  • Redshift: Light sources retreating.

Standing Waves

  • Standing Wave: Stationary waveform from interference of waves in opposite directions, exemplified with ropes.- Form only at particular frequencies.

Resonance

  • Resonance: Wave phenomenon where external force matches an object's natural frequency, leading to amplified vibrations.- Example: A swing requires pushes at specific intervals for continued motion.

Resonance Example with Tuning Forks

  • One struck tuning fork causes a second fork of matching frequency to vibrate due to sound wave energy.

Musical Instruments and Standing Waves

  • Instruments utilize standing waves for tone production:- Strings adjust tension to modify vibration frequency, altering pitch.

    • Instrument bodies act as resonance cavities, enhancing sound volume.