JEE Advanced · 2026 · 17 May 2026 · Paper 1 · Waves & Sound

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List-I shows four configurations made of straight and semi-circular narrow tubes containing air. A sound wave of wavelength

λ = 0.29 m

enters these structures at the point

S

and a sound detector is placed at

D

. Between the points

S

and

D

, the sound travels only through the tubes. List-II contains the possible smallest values of

l

(refer to the figures) for which the detector

D

records maximum amplitude. Ignore effects of sharp corners. [Given

cos (1 5^{\circ}) = 0.97

]
Choose the option that best describes the match between the entries in List-I to those in List-II.

(A)P→4, Q→3, R→5, S→1
(B)P→4, Q→3, R→1, S→5
(C)P→3, Q→4, R→1, S→2
(D)P→3, Q→4, R→5, S→2✓ Correct

Answer: (D)

Solution

(P) Path difference:

Δ x = (π - 2) \frac{ℓ}{2}

. For maxima:

ℓ_{m i n} = \frac{2 λ}{π - 2} = 0.51

m → (3)

(Q) Path difference:

Δ X = ℓ

. For maxima:

ℓ_{m i n} = λ = 0.29

m → (4)

(R) Path difference:

Δ X = \frac{π ℓ}{2}

. For maxima:

ℓ_{m i n} = \frac{2 λ}{π} = 0.13

m → (5)

(S) Path difference:

Δ x = 0.249 ℓ

. For maxima:

ℓ_{min} = λ /0.249 \approx 1.19

m → (2)

Note: List-II has (5) 0.13 m appearing, which matches R, but the answer key shows S→2 (not listed in visible List-II). Based on source solution, the correct matching is P→3, Q→4, R→5, S→2.

JEE Advanced · 2026 · 17 May 2026 · Paper 1 · Single correct option

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JEE Advanced · 2026 · 17 May 2026 · Paper 1 · Waves & Sound

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