JEE Main · 2019 · 12 Apr 2019 · Shift 2 · Waves & Sound

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A tuning fork of frequency 480 Hz is used in an experiment for measuring speed of sound (v) in air by resonance tube method. Resonance is observed to occur at two successive lengths of the air column,

ℓ_{1} = 30 cm

and

ℓ_{2} = 70 cm

. Then n is equal to :

(A) $332 ms^{- 1}$
(B) $338 ms^{- 1}$
(C) $384 ms^{- 1}$ ✓ Correct
(D) $379 ms^{- 1}$

Answer: (C)

Solution

In a resonance tube, consecutive resonances are half a wavelength apart, so

\frac{λ}{2} = ℓ_{2} - ℓ_{1} = 70 - 30 = 40

cm, giving

λ = 80

cm. The speed of sound is then

v = f λ = 480 \times 0.80 = 384

m/s.

JEE Main · 2019 · 12 Apr 2019 · Shift 2 · Single correct option

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