JEE MAIN - Physics (2022 - 29th June Evening Shift - No. 21)
In an experiment to determine the velocity of sound in air at room temperature using a resonance tube, the first resonance is observed when the air column has a length of 20.0 cm for a tuning fork of frequency 400 Hz is used. The velocity of the sound at room temperature is 336 ms$$-$$1. The third resonance is observed when the air column has a length of _____________ cm.
Answer
104
Explanation
$$400 = {v \over {4({L_1} + e)}}$$ ..... (i)
$$400 = {{5v} \over {4({L_2} + e)}}$$ ..... (ii)
$$ \Rightarrow {L_1} + e = {\lambda \over 4} = 21$$ cm
$${L_2} + e = {{5\lambda } \over 4} = 105$$ cm
$$\Rightarrow$$ e = 1 cm & L2 = 104 cm
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