Physics Notes: Waves and Sound

Definition of Waves

A wave is a disturbance or a propagation that may lead to the transfers of energy from one point to another .

Classification of Waves

Common Wave Terms

• Amplitude: Maximum displacement from rest position
• Wavelength (λ): Distance between two consecutive crests or troughs
• Period (T): Time for one complete wave cycle
• Frequency (f): Number of wave cycles per second → f = 1 / T
• Wave Speed (v): v = f × λ

Wave Phenomena

Diffraction: Bending of waves around obstacles or through gaps
Example: Sound heard around corners

Interference: When two waves resulting in reinforcement or cancellation of each other
Example: Ripple patterns in water

Refraction: Change in wave direction due to change in speed across media
Example: Water waves slowing in shallow regions

Sound

Bell Jar Experiment
Aim: To show that sound needs a medium to travel.
Procedure:

• Place an electric bell inside a sealed bell jar.
• Connect the bell to a power source — it rings.
• Use a vacuum pump to remove air from the jar.
• As air is removed, the sound fades.

Diagram: Bell inside jar with vacuum pump
Conclusion: Sound cannot travel through a vacuum.

Sound Refraction Experiment
Aim: To demonstrate refraction of sound using a wall, clapper, and stopwatch.
Procedure:

• Place a wall between two students.
• One claps; the other listens and times the sound using a stopwatch.
• Repeat without the wall and compare times.

Diagram: Wall, clapper, listener, stopwatch. Conclusion: Sound bends (refracts) around obstacles; speed may vary.