NEET Physics - Chapter 17
Resonance Tube – Complete Notes, Revision, Important Questions & Downloads
Resonance Tube focuses on the TOC subtopic Sound Velocity Measurement by Resonance, where a variable air column in a closed pipe is tuned to match a fork frequency. The method uses first and second resonance lengths with end correction to extract wavelength by lambda = 2(l2 - l1). Once wavelength is known, sound speed is obtained from v = n lambda, so the practical working formula becomes v = 2n(l2 - l1). NEET tests this topic through direct numericals on resonance lengths, correction-aware interpretation, and checks on why second resonance appears beyond three times the first effective length.
Air Column ResonanceMeasurement MethodNCERT-Aligned
Expected QuestionsQ
1
Usually one direct numerical or method-based conceptual question appears from resonance-length relations and sound-speed calculation.
Time Required⏱
1 h
Around 25 minutes to lock equations and physical setup, 25 minutes to solve mixed numericals, and 10 minutes for trap revision.
Difficulty⚡
Medium
Formula count is small, but errors occur when students ignore end correction logic or misuse first and second resonance relations.
NRI USA Curriculum GapUS
Bridge Needed
US high-school wave labs often stay qualitative, while NEET expects fast equation-level extraction of wavelength and velocity from measured resonant lengths.
5Subtopics
20Practice Questions
4Free Downloads
1 hPrep Time
Resonance Tube Weightage and Trend
Waves and Sound - Topic 19| NEET Year | Questions from this Topic | Bar | Marks |
|---|---|---|---|
| 2020 | 1 | 4 | |
| 2021 | 0 | 0 | |
| 2022 | 1 | 4 | |
| 2023 | 1 | 4 | |
| 2024 | 1 | 4 | |
| 2025 | 0 | 0 | |
| Estimated resonance-tube-linked asks in recent NEET papers | 4 | 16 |
Most resonance-tube questions start from two observed loud positions, then require extracting lambda using l2 - l1 without needing explicit end correction value.
When both first and second resonance equations are written, end correction cancels in subtraction, which is the scoring shortcut in objective exams.
A common application is computing sound speed at room conditions with known fork frequency, where unit consistency in length conversion decides final accuracy.
When both first and second resonance equations are written, end correction cancels in subtraction, which is the scoring shortcut in objective exams.
A common application is computing sound speed at room conditions with known fork frequency, where unit consistency in length conversion decides final accuracy.
0.7
Avg Questions / Year
16
Total Marks (6 yrs)
Direct
Pattern
Medium
Difficulty
5-Step Resonance Tube Solve Routine
1
Write the two resonance equations first Start with l1 + e = lambda/4 and l2 + e = 3lambda/4 before any number substitution; this protects you from skipping the physical condition of closed-pipe resonance.
2
Eliminate end correction by subtraction Subtract the two equations to get lambda = 2(l2 - l1), then convert all lengths into SI units to prevent decimal mistakes in velocity.
3
Use fork frequency only after wavelength Compute v = n lambda in the last step so that mode relation and measurement geometry remain separated and easier to verify.
4
Check second resonance placement Use l2 = 3l1 + 2e to verify that second resonance appears at length greater than three times first resonance length, which is a quick plausibility test.
5
Run a trap audit on symbols Confirm n means tuning-fork frequency, not mode count, and ensure l1 and l2 are resonance lengths from the same fork in identical tube conditions.
Resonance Tube Download Kit
PDF · Cheat Sheet · MCQ Set · PYQFull Notes
Complete notes on resonance tube setup, end correction idea, first-second resonance equations, and velocity extraction workflow.
Download PDFFormula Sheet
One-page formula map with l1 + e = lambda/4, l2 + e = 3lambda/4, lambda = 2(l2 - l1), and v = 2n(l2 - l1).
Download PDFMCQ Practice
Application-first questions on wavelength calculation from resonance lengths and speed-of-sound estimation for different fork frequencies.
Download PDFPYQ Workbook
Year-tagged and NEET-style resonance problems with trap annotations on end correction cancellation and symbol interpretation.
Download PDFSubtopics in Resonance Tube
2-Column TableRapid Revision Cards
Concept → Trap → Example1) Sound Velocity Measurement by Resonance
Resonant-length methodFor first and second resonances: l1 + e = lambda/4 and l2 + e = 3lambda/4, so lambda = 2(l2 - l1) and v = n lambda = 2n(l2 - l1).
- Apply this when two loud positions are measured with one tuning fork over a resonance tube having variable air-column length.
- Ensure both lengths come from the same fork frequency and stable room conditions before computing lambda and v.
- Trap: many students insert l2 = 3l1 directly and ignore end correction term, which distorts the relation unless e is handled correctly.
Example (NEET-style)If n = 512 Hz, l1 = 0.16 m and l2 = 0.49 m, then lambda = 2(0.49 - 0.16) = 0.66 m. Hence v = 512 x 0.66 = 337.92 m/s, which is close to room-temperature sound speed.
Curriculum Gap: India vs USA
Two concrete preparation gaps to bridge for NEET readinessAP Physics 1 covers resonance conceptually; NEET expects equation-level tube measurements
AP Physics 1 labs frequently emphasize qualitative resonance behavior, but NEET asks fast numerical extraction of wavelength and velocity using first and second resonance lengths.
- Practice at least 25 mixed problems where lambda is obtained from l2 - l1 before any velocity computation.
- Memorize when end correction cancels and when it appears explicitly in equation checks.
AP Physics C mathematical fluency is high, but NEET objective traps are format-specific
AP Physics C students can manipulate equations well, yet NEET options often exploit symbol confusion among frequency, harmonic index, and resonance-order language.
- Adopt a fixed solve sequence: write resonance equations, subtract, compute lambda, then compute velocity.
- Maintain an error log specifically for unit conversion slips and misuse of l2 = 3l1 + 2e.
NEET-style practice questions
2 MCQs1In a resonance tube experiment with tuning fork frequency 480 Hz, first and second resonance lengths are 17 cm and 52 cm. The speed of sound in air is closest to:Sound Velocity Measurement by Resonance
288 m/s
336 m/s
384 m/s
432 m/s
Use the resonance-tube relation lambda = 2(l2 - l1). Convert lengths to SI first: l1 = 0.17 m, l2 = 0.52 m, so l2 - l1 = 0.35 m. Therefore lambda = 2 x 0.35 = 0.70 m. Sound speed is v = n lambda = 480 x 0.70 = 336 m/s. Option C comes from forgetting the factor 2 in lambda = 2(l2 - l1). Option D usually appears when students multiply by resonance order wrongly, and option A comes from incorrect centimeter-to-meter conversion.
2For a resonance tube, if end correction is e and first resonance length is l1, the second resonance length l2 satisfies:Sound Velocity Measurement by Resonance
l2 = 2l1 + e
l2 = 3l1
l2 = 3l1 + 2e
l2 = l1 + 2e
Write the two resonance conditions: l1 + e = lambda/4 and l2 + e = 3lambda/4. Divide the second by the first to get (l2 + e)/(l1 + e) = 3. Rearranging gives l2 + e = 3l1 + 3e, so l2 = 3l1 + 2e. This is why the textbook notes that second resonance is obtained at a length more than three times the first resonance length. Option B ignores end correction and is only approximate when e is negligible, while options A and D do not follow from the resonance equations.
Practice Questions
Click "Reveal Answer" after attempting1A tuning fork of frequency 256 Hz gives first and second resonances in a tube at 18 cm and 50 cm. Find the speed of sound.
131.1 m/s
163.8 m/s
327.7 m/s
655.4 m/s
👁 Reveal Answer
Correct option: B. Using lambda = 2(l2 - l1), convert lengths: l1 = 0.18 m and l2 = 0.50 m. So lambda = 2 x (0.50 - 0.18) = 0.64 m. Then v = n lambda = 256 x 0.64 = 163.84 m/s. Option C comes from using lambda = l2 - l1 without factor 2 and then doubling later by mistake, while option D doubles the correct speed again by incorrectly adding resonance order into the final formula.
2In a resonance tube experiment, l2 - l1 = 34 cm for a fork of 500 Hz. The wavelength and sound speed are:
0.34 m, 170 m/s
0.68 m, 340 m/s
1.36 m, 680 m/s
0.17 m, 85 m/s
👁 Reveal Answer
Correct option: B. Since lambda = 2(l2 - l1), with l2 - l1 = 0.34 m we get lambda = 0.68 m. Then v = n lambda = 500 x 0.68 = 340 m/s. Option A misses the factor of 2 in wavelength relation, option C doubles both wavelength and speed without physical basis, and option D halves wavelength incorrectly by treating l2 - l1 as lambda/2 again after already using the relation.
3If l1 = 14 cm and end correction e = 1 cm, what is l2 according to resonance-tube relation?
42 cm
44 cm
46 cm
48 cm
👁 Reveal Answer
Correct option: B. Use l2 = 3l1 + 2e from (l2 + e)/(l1 + e) = 3. Substituting l1 = 14 cm and e = 1 cm gives l2 = 3 x 14 + 2 x 1 = 44 cm. Option A ignores the 2e correction term, option C adds an extra 2 cm without basis, and option D usually comes from multiplying the effective first length by 3 and then adding e twice again.
4For a fixed fork frequency, if measured l2 - l1 is larger in one day than another day, which statement is correct?
Wavelength is smaller and sound speed is smaller
Wavelength is larger and sound speed is larger
Wavelength is unchanged but speed is larger
Wavelength is larger but speed is unchanged
👁 Reveal Answer
Correct option: B. Resonance relation gives lambda = 2(l2 - l1), so larger separation directly means larger wavelength. With the same fork, frequency n is fixed, and v = n lambda, so speed also increases proportionally. Option C is impossible because fixed frequency and changed wavelength must change speed. Option D wrongly assumes speed is independent of wavelength even though v and lambda are linked by v = n lambda for a fixed source frequency.
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Frequently Asked Questions
Notes · Downloads · Revision · Important QuestionsWhy do we use two resonance lengths instead of only the first one to find sound velocity?
Using first and second resonance together allows subtraction of equations so end correction cancels naturally. If only the first resonance is used, the unknown end correction must be estimated separately and can introduce error. The pair method gives a cleaner wavelength estimate through lambda = 2(l2 - l1), then velocity follows from v = n lambda with fewer assumptions.
Does end correction always have to be known numerically in NEET resonance-tube problems?
Not always. In many objective problems based on first and second resonances, you do not need a numeric value of e because it is eliminated by subtraction. However, when the question directly asks relation between l1 and l2 or gives one resonance condition only, end correction terms must be retained in symbolic form to avoid wrong approximation.
What is the physical meaning of the loud note heard at resonance?
The loud note indicates maximum energy transfer from tuning fork to the air column when driving frequency matches the natural frequency of an allowed mode. At this condition, standing-wave amplitude inside the tube grows significantly compared with non-resonant lengths. In exam language, this loudness is the practical marker for selecting l1, l2, and higher resonant positions.
Can temperature change affect resonance-tube numerical answers?
Yes, because speed of sound in air depends on temperature, so resonance length spacing for a fixed fork can shift. If the problem gives room conditions explicitly, use those values as stated. If speed is to be computed from measured lengths and known fork frequency, the result already reflects that temperature condition, so avoid adding extra correction unless requested.
Why is the second resonance length more than three times the first resonance length?
From the equations l1 + e = lambda/4 and l2 + e = 3lambda/4, division gives l2 + e = 3(l1 + e). Rearranging gives l2 = 3l1 + 2e, which is greater than 3l1 because e is positive. This result is a quick conceptual check in objective questions and helps reject options that state l2 equals exactly 3l1.
What is the most common calculation error in this topic?
The most common error is treating l2 - l1 directly as wavelength, while the correct relation is lambda = 2(l2 - l1). This halves or doubles final velocity depending on downstream arithmetic. Another frequent mistake is keeping lengths in centimeters while velocity is expected in m/s, which creates option-level mismatch even when the formula idea is right.
Do we need harmonic-number formulas of open and closed pipes separately for resonance tube questions?
For core resonance-tube numericals, the two-length method is usually sufficient. Still, understanding closed-pipe mode logic helps explain why the resonance sequence is odd-mode based and why positions appear in that pattern. This background reduces memorization and makes relation checks like l2 = 3l1 + 2e feel physically justified rather than purely algebraic.
How should an NRI student from AP Physics background practice this topic for NEET?
Focus on objective-speed execution rather than descriptive lab reports. Build a short routine: write both resonance equations, eliminate e, compute wavelength, then compute velocity with unit check. Practice 30 to 40 mixed questions where numeric data are intentionally close, because NEET options often test whether you preserved factor 2 and SI conversion correctly.
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