Knowt
3 - Waves (Sound & Light)
General Properties of Waves
Definition of a Wave
A wave is defined as a disturbance that transfers energy through matter or space without transferring matter. This means that waves can propagate through different mediums or even through a vacuum, such as in the case of electromagnetic waves.
Types of Waves
Mechanical Waves: These waves require a medium (like air, water, or solid material) to travel through. Examples include sound waves and ocean waves. They can be further divided into:
Longitudinal Waves: Where particles of the medium vibrate parallel to the direction of wave motion. Examples include P-waves (primary waves) and sound waves.
Transverse Waves: Where particles of the medium vibrate perpendicular to the direction of wave motion. Examples include S-waves (secondary waves) and electromagnetic waves such as light.
Non-Mechanical Waves: These waves do not require a medium to propagate. They can travel through a vacuum, making them crucial in contexts like solar radiation, which reaches Earth from the Sun. Examples include electromagnetic waves such as radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
Key Definitions
Wavelength (λ): The distance between two consecutive crests or troughs of a wave, measured in meters (m).
Frequency (f): The number of complete waves that pass a given point in one second, measured in Hertz (Hz). This indicates the pitch of a wave in sound.
Speed (v): The rate at which a wave travels through a medium, typically measured in meters per second (m/s). The speed of sound, for instance, varies across different mediums.
Time Period (T): The duration of time it takes for one complete wave cycle to pass a given point, measured in seconds (s).
Crest: The highest point of a wave, representing maximum energy transfer in the case of transverse waves.
Trough: The lowest point of a wave, indicating minimum displacement from the resting position in transverse waves.
Amplitude: The height of the wave from the rest position to either the crest or trough, which directly relates to the wave's energy and intensity.
Wavefront: An imaginary line or surface that connects points of equal phase along a wave.
Wave Comparisons
Longitudinal Waves: The particles in these waves move parallel to the direction of the wave's propagation. An example is sound, where compressions and rarefactions move along a medium.
Transverse Waves: In these waves, the particle movement is perpendicular to the wave's motion. This is typical in water waves and light waves.
Wave Effects
Reflection: The bouncing back of a wave when it encounters a barrier; this principle is fundamental in acoustics and optics, affecting how we perceive sound and light.
Refraction: The bending of a wave as it passes from one medium to another, which alters its speed and wavelength while keeping frequency constant. This principle underlies the functioning of lenses.
Diffraction: The phenomenon by which waves spread out as they pass through a narrow opening or around obstacles. It explains the spreading pattern of sound and light waves as well as the principles behind certain optical instruments.
Speed of Sound
The speed of sound varies significantly across different mediums:
Air: Approximately 330 - 350 m/s depending on temperature and humidity.
Water: Around 1500 m/s, making it much faster due to closer molecular interactions.
Solid: About 4000 m/s, as the densely packed molecules transmit the sound waves more efficiently.
Factors Affecting Sound Speed:
Temperature: Higher temperatures increase the speed of sound, as warmer molecules vibrate more rapidly.
Pressure: Changes in pressure can affect sound speed, but in ideal gases, the effect is minimal compared to temperature changes.
Sound Properties
Pitch: The perceived frequency of sound; higher frequencies correspond to higher pitches, essential in music and communication.
Loudness: The perceptual response to the amplitude of sound waves, measured in decibels (dB). The greater the amplitude, the louder the sound.
Audible Range: Humans typically can hear sounds between 20 Hz and 20,000 Hz (20 kHz). Sounds below 20 Hz are known as infrasound, while those above 20,000 Hz are termed ultrasound.
Light Properties
Spectrum of White (Visible) Light
VIBGYOR: Represents the visible spectrum colors - Violet, Indigo, Blue, Green, Yellow, Orange, and Red, which illustrates how light can be broken down into its constituent colors.
As light transitions from red to violet, its frequency increases while its wavelength decreases.
Reflection of Light: Governed by the law that the angle of incidence (i°) equals the angle of reflection (r°), crucial for understanding mirrors and optical instruments.
Plane Mirror Formation: In a plane mirror, the size of the image is identical to the object's size, and the image appears laterally inverted, influencing design in everyday applications.
Refraction of Light: Light bends when transitioning between mediums. This bending is explained by Snell's Law, which relates incident and refracted angles.
Total Internal Reflection: Occurs when light attempts to pass from a denser medium to a rarer one, with the angle of incidence exceeding the critical angle—essential for fiber optics technology.
Lenses
Convex Lens: These lenses converge parallel rays of light to a focal point, playing a key role in magnifying images in devices like glasses and cameras.
Ray Diagrams: Essential for understanding image formation based on object position relative to the focal points (F and 2F).
Concave Lens: Diverges light rays, making them appear as if they come from a focal point behind the lens, which is vital for correcting short-sightedness (myopia).
Applications of Lenses
Long-Sightedness (Hyperopia): A condition that is corrected using convex lenses that help focus images on the retina.
Short-Sightedness (Myopia): Corrected with concave lenses, allowing clear vision of distant objects.
Electromagnetic Waves
Types: Include a wide range of wavelengths and frequencies, categorized from radio waves and microwaves to infrared and visible light, ultraviolet, X-rays, and gamma rays.
Use Cases: Vital across various fields including telecommunications, medical imaging, and thermal imaging.
Harmful Effects: Certain frequencies, particularly in ultraviolet and X-ray ranges, can lead to skin burns, cancer, and vision issues, necessitating protective measures in usage.
This comprehensive overview of wave properties serves to deepen the understanding of both mechanical and non-mechanical waves, their behaviors, and their significance in various scientific and practical applications.
