Sound and Music

Sound and music are created by varying the frequency of sound waves, producing different notes.

1. String Instruments: Instruments like the sitar, violin, and guitar use strings to create sound.

The frequency of the string is altered by:

• Adjusting string tension.
• Changing the vibrating length of the string using fingers.

2. Wind Instruments: Instruments like the flute and shehnai create sound by vibrating air columns.

The frequency is changed by:

• Opening or closing holes to adjust the air column length.
• Changing the method of air-blowing to vary the sound.

When musicians tune their instruments, they adjust the pitch to make sure the sound matches the required notes.

• Tanpura: A singer adjusts the tension of the strings to produce the correct notes.
• Tabla: The tabla player uses a hammer to tighten or loosen the pegs to change the tension of the membrane.
• Harmonium: The harmonium player finds the correct key that matches the singer’s pitch.

Pitch and Frequency: Pitch refers to how high or low a sound is. Frequency determines the pitch-the higher the frequency, the higher the pitch. In Indian music, the notes Sa, Re, Ga, Ma, Pa, Dha, and Ni have increasing pitch in that order.

String vibration and periodic motion: When a string on an instrument (like a tanpura) is plucked, it vibrates, but the two ends stay still. The string moves back and forth repeatedly at regular intervals. This repeated motion is called periodic motion.

Tuning the instruments

1. Aim: To observe how the height of the air column in glass cups affects the frequency of sound generated and to explore the relationship between air column height and frequency.

2. Requirements: 6-7 glass cups or glasses, water, a pencil or stick to strike the cups, and a smartphone app for measuring sound frequency (optional).

3. Procedure

• Arrange 6-7 glass cups in a straight line.
• Fill each glass with increasing levels of water, from least to most.
• Strike the glasses gently with a pencil or stick.
• Listen to the unique sound produced by each glass.
• Use a smartphone app to measure the frequency of the sound from each glass.

4. Observation: When each glass is struck, a unique sound is produced. The frequency of the sound depends on the height of the air column above the water level.

Less water = taller air column → lower frequency → deeper sound.

More water = shorter air column → higher frequency → sharper sound.

5. Conclusion: The frequency of sound depends on the height of the air column above the water. Taller air columns create lower-frequency sounds, while shorter air columns produce higher frequencies. This demonstrates the principle behind musical instruments like the Jaltarang.