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🌊 WAVES (Mechanical Waves)

Stage 2 – Page 7 : Resonance Tube Experiment & Velocity of Sound


1️⃣ What Is Resonance?

Resonance occurs when the frequency of the sound source matches the natural frequency of the air column.

At resonance → amplitude becomes maximum → sound becomes loud.


2️⃣ Resonance Tube Experiment Setup

  • Vertical glass tube partially filled with water
  • Tuning fork of known frequency
  • Air column above water acts as a closed pipe

3️⃣ Resonance Condition for Closed Pipe

Leff = (2n − 1) λ / 4

Only odd harmonics are possible.


4️⃣ First Resonance (Fundamental)

L₁ + e = λ / 4

This gives the smallest air column length.


5️⃣ Second Resonance

L₂ + e = 3λ / 4

Difference between two resonance lengths eliminates end correction.


6️⃣ Key Relation (Most Important)

L₂ − L₁ = λ / 2

This relation is heavily used in JEE numericals.


7️⃣ Velocity of Sound Formula

v = fλ

Using resonance:

v = 2f (L₂ − L₁)


8️⃣ Why Use Difference of Lengths?

  • End correction cancels out
  • Gives more accurate velocity
  • Used in experiments & exams

9️⃣ JEE-Type Conceptual Traps

  • Resonance tube is always a closed pipe
  • Do not apply open pipe formula
  • Use L₂ − L₁, not absolute length

🔟 Typical JEE Question

Given f = 512 Hz, L₁ = 16 cm, L₂ = 49 cm. Find velocity of sound.

Method: v = 2f (L₂ − L₁)


➡️ Next Page Preview

  • Beats & beat frequency
  • Applications in sound tuning

Stage 2 – Page 7 Completed Successfully ✅

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