Waves and Oscillations

What is wave?

is a disturbance that transfers energy from one place to another without transferring matter. Waves are fundamental in describing many physical phenomena, such as sound, light, and water motion.

Mechanical Waves:

Require a medium to propagate (e.g., sound waves, water waves).

What are the 2 types of Mechanical Waves?

Transverse Waves, and Longitudinal Waves

Transverse Waves:

Particles move perpendicular to the direction of wave propagation (e.g., waves on a string, electromagnetic waves),

Longitudinal Waves:

Particles move parallel to the wave propagation (e.g., sound waves).

ROYGBIV

Red, Orange, Yellow, Green, Blue, Indigo, Violet

Electromagnetic Waves:

Do not require a medium and travel through vacuum (e.g., light, radio waves).

Basic Wave Properties

Amplitude (A): Maximum displacement of a wave from its equilibrium position.

Wavelength (λ): The distance between two consecutive crests or troughs.

Frequency (f): The number of oscillations or cycles per unit of time, typically measured in Hertz (Hz).

Period (T): The time taken for one complete cycle of the wave (T = 1/f).

Wave Speed (v): The speed at which the wave propagates through the medium.

Properties of sound

Frequency, Pitch, Amplitude, and Speed of Sound

Frequency:

• Definition: The number of complete vibrations or cycles a wave undergoes per unit of time.

• Unit: Hertz (Hz) — 1 Hz = 1 cycle per second.

Effect on Sound: Higher frequency corresponds to a higher pitch (e.g., a high-pitched whistle), while lower frequency corresponds to a lower pitch (e.g., a bass drum)

Pitch:

Definition: The perceptual quality of sound that allows us to classify sounds as high or low.

Relation to Frequency: The pitch of a sound is directly related to its frequency — higher frequencies produce higher pitches, and lower frequencies produce lower pitches.

Example: The pitch of a piano note increases as you move from the left (low frequency) to the right (high frequency) on the keyboard.

Amplitude:

Definition: The maximum displacement of particles from their equilibrium position.

Relation to Sound: The greater the amplitude, the louder the sound. Amplitude is associated with the loudness of the sound.

Example: A large amplitude produces a loud sound (like a drumbeat), while a small amplitude produces a quieter sound (like a whisper).

Speed of Sound:

Definition: The speed at which sound waves travel through a medium.

In Air: Around 343 m/s at 20°C (this speed can change with temperature, humidity, and air pressure).

In Water: Around 1480 m/s.

In Solids: Speed is higher (e.g., around 5000 m/s in steel).

Wave Behaviors

Reflection, Refraction, Diffraction, and Interference

Reflection:

Definition: When a wave strikes a surface and bounces back.

Example: Echoes are produced when sound waves reflect off a hard surface (like a wall or mountain).

Law of Reflection: The angle of incidence (incoming wave) equals the angle of reflection (reflected wave).

Refraction:

Definition: The bending of a wave as it passes from one medium to another, causing a change in speed.

Example: When sound waves pass from air into water, their speed changes, and they bend.

Key Concept: The change in speed leads to a change in direction.

Diffraction:

Definition: The bending of waves around obstacles or through openings.

Example: Sound waves diffract around corners, which is why you can hear someone talking even when you can’t see them.

Key Concept: The extent of diffraction depends on the size of the obstacle relative to the wavelength. Longer wavelengths diffract more than shorter ones.

Interference:

Definition: When two or more waves meet and combine. This can lead to constructive or destructive interference.

Constructive Interference: When waves combine to create a wave of greater amplitude.

Destructive Interference: When waves combine to cancel each other out.

Example: When two sound waves are in phase, they amplify each other (constructive), but if they are out of phase, they cancel each other (destructive).

Wave Speed

v= f⋅λ

• vv = wave speed (m/s)

• ff = frequency (Hz)

• λλ = wavelength (m)

Frequency and Period Relationship

f=1/T

• ff = frequency (Hz)

• TT = period (s)

Speed of Sound in Air

v≈343 m/s at 20∘C

Sound Intensity

I=p/a

• II = intensity (W/m²)

• PP = power (W)

• AA = area (m²)

Quiz Bee Tip:

If you're joining quiz bees, focus more on:

v=fλv=fλ

f=1/Tf=1/T

Speed of sound = 343 m/s

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