Waves, Sound and Light

WAVES, SOUND AND LIGHT

Definition of a Pulse: A single disturbance that is propagated by a medium.
Example: Flicking a hose or rope to overcome an obstacle produces a pulse in the medium (the hose).
Amplitude (A): The maximum disturbance of a particle from its position of rest (equilibrium position).
Position of Rest: No movement is present in the medium, indicating it is at rest.
Direction of Movement: As the pulse moves, each point on the hose moves up and down, creating a transverse pulse.
Energy and Amplitude: The amplitude reflects the energy transferred by the pulse. More energy results in a greater amplitude.

Amplitude (A): Measure of energy in the pulse.
Pulse Length: The distance between the start and end of a pulse.
Speed of a Pulse: Calculated using the equation for speed:
- v = \frac{D}{\Delta t}
- Where:
- D: Distance covered (in meters)
- Δt: Change in time (in seconds)
Example Calculation of Pulse Speed:
- If it takes 0.2 s for a pulse to cover 300 mm (0.3 m):
- v = \frac{0.3}{0.2} = 1.5 \text{ m/s}
Practical Calculation: For a speed of a pulse of 0.032 m/s over 2 minutes:
- Total time = 2 min = 120 s.
- D = 0.032 \times 120 = 3.84 m

Movement Types:
- Movement of pulse (transverse)
- Movement of particles in the medium
These movements are perpendicular to each other in transverse pulses.

Interference: The interaction of two pulses in the same medium when they meet.
- Classified as either constructive or destructive interference.
Constructive Interference: Two pulses meet on the same side of the rest position, combining to form a greater amplitude. After overlapping, they maintain their original direction and amplitude.
Destructive Interference: Occurs when two pulses meet on opposite sides of the rest position, yielding a smaller amplitude. After interference, they proceed in their original directions with their original amplitudes.
Superposition: The algebraic sum of the amplitudes of overlapping pulses at the same space at the same time.

Constructive Interference: Pulses meet on the same side:
- Resulting displacement = algebraic sum of displacements.
- Resulting amplitude increases.
Destructive Interference: Pulses meet on opposite sides:
- Resulting displacement = vector sum of displacements.
- If equal amplitudes, they can fully cancel each other out.

Transverse Wave: A wave in which the particles of the medium vibrate perpendicular to the direction of motion of the wave.

Amplitude (A): Maximum particle displacement from the position of rest (in meters).
Rest Position: The natural position without disturbance.
Crest (V): The highest point of a wave.
Trough (X): The lowest point of a wave.
Wavelength (λ): Distance between consecutive points in phase (in meters).
Frequency (f): Number of wave pulses passing a point per second (in hertz, Hz).
Period (T): Time for one complete wave to pass a point (in seconds, s).
Wave Speed (v): Calculated as:
- v = f \lambda
- Speed is influenced by:
- Density of the medium
- Tension of the medium
- Elasticity of the medium

Longitudinal Wave: A wave where the particles of the medium vibrate parallel to the wave direction.

Compressions: Regions of high pressure where particles are close.
Rarefactions: Regions of low pressure where particles are farther apart.
Wavelength (λ): Distance between two consecutive points in phase (in meters).
Amplitude: Maximum particle displacement from equilibrium.
Frequency (f): Number of complete wavelengths passing a point in one second.
Period (T): Time taken for one wave pulse to move past a fixed point.
Wave Speed (v): Calculated using the same formulas as transverse waves.

Definition: Sound is propagated through vibrations and requires a medium (e.g., air) for transmission.
Mechanism: A loudspeaker causes air particles to compress and rarefy, creating longitudinal waves that travel toward the ear.
Frequency and Pitch: Higher frequency correlates with a higher pitch, while lower frequency correlates with a lower pitch.
Loudness: Determined by amplitude; greater amplitudes equal louder sounds. Loudness is measured in decibels (dB).
Quality: Refers to the timbre of sound; pure notes have regular patterns, while noises have irregular wave patterns.

Ultrasound: Frequencies above 20,000 Hz, used in various applications such as medical imaging and sonar.
Characteristics: Sound cannot travel in a vacuum (i.e., space).

Definition: EM waves have wave properties (like reflection, refraction) and particle properties (like photons).
Propagation: Do not require a medium, travel at the speed of light (approximately 3 \times 10^8 \, \text{m/s}).

Arranged by increasing frequency and decreasing wavelength:
- Radio Waves → Microwaves → Infrared → Visible Light → Ultraviolet → X-rays → Gamma Rays
Wavelengths & Frequencies:
- Radio Waves (longest wavelength, lowest frequency)
- Gamma Rays (shortest wavelength, highest frequency)

Energy Equation: The energy of a photon (quantum of energy) can be calculated:
- E = hf
- Where:
- E: Energy of photon (in joules)
- h: Planck's constant ($6.63 \times 10^{-34} \, \text{J s}$)
- f: Frequency (in hertz)

Ultrasound Uses: In sonar, medical diagnostics, and nature observation.
Reflection and Medical Uses: Ultrasound imaging for pregnancy and treatments, like breaking kidney stones.

EM radiation possesses both wave and particle characteristics, being made up of photons that carry energy. All EM waves travel at the speed of light in a vacuum, exhibit various wavelengths and frequencies, and can be defined and quantified through their energy properties.