Two loudspeakers (L_1 and L_2) are placed… - JEE Main 2026 Physics PYQ

JEE Main 2026 — Physics Waves & Oscillations

2026integermedium

Two loudspeakers ( $L_{1}$ and $L_{2}$ ) are placed with a separation of 10 m, as shown in figure. Both speakers are fed with an audio input signal of same frequency with constant volume. A voice recorder, initially at point $A$ , at equidistance to both loud speakers, is moved by 25 m along the line $A B$ while monitoring the audio signal. The measured signal was found to undergo 10 cycles of minima and maxima during the movement. The frequency of the input signal is $\_\_\_\_$ Hz (Speed of sound in air is $324 \mathrm{~m} / \mathrm{s}$ and $\sqrt{5}=2.23$ )

JEE Main 2026 Physics, Waves and Sound — question figure

Official previous-year question

Held on 22 Jan 2026 · Verified 6 Jul 2026.

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Solution

Point B will $10^{\text {th }}$ maxima

$\Delta x=L_2 B-L_1 B$

$L_1 B=\sqrt{20^2+40^2}=20 \sqrt{5} \mathrm{~m}=44.6 \mathrm{~m}$

$L_2 B=\sqrt{40^2+30^2}=50 \mathrm{~m}$

$\Delta x=50-44.6=5.4 \mathrm{~m}$

$\Delta x=n \lambda$

$5.4=10 \times \lambda$

$\lambda=0.54 \mathrm{~m}$

$V=f \lambda$

$f=\frac{324}{0.54}=600 \mathrm{~Hz}$

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