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JEE Main 201815 AprilEvening ShiftOnline
Exam
JEE Main
Year
2018
Date
15 April
Shift
Evening Shift
Mode
Online
Subject
Physics
Chapter
Waves and Sound

JEE Main 2018 · 15 April · Evening Shift · Online · Physics · Waves and Sound

5 beats/ second are heard when a turning fork is sounded with a...

5 beats/ second are heard when a turning fork is sounded with a sonometer wire under tension, when the length of the sonometer wire is either 0.95 m0.95 \mathrm{~m} or 1 m1 \mathrm{~m}. The frequency of the fork will be:

Options

  1. A195 Hz195 \mathrm{~Hz}
  2. B251 Hz251 \mathrm{~Hz}
  3. C150 Hz150 \mathrm{~Hz}
  4. D300 Hz300 \mathrm{~Hz}

Correct answer

A. 195 Hz195 \mathrm{~Hz}

Step-by-step solution

Probable frequencies of tuning fork be n±n \pm 5 Frequency of sonometer wire, n∝1ln \propto \frac{1}{l} ∴n+5n−5=10095⇒95(n+5)=100(n−5) or, 95n+475=100n−500 or, 5n=975 or, n=9755=195 Hz\begin{aligned} &\therefore \frac{n+5}{n-5}=\frac{100}{95} \Rightarrow 95(n+5)=100(n-5) \\ &\text{ or, } 95 n+475=100 n-500 \\ &\text{ or, } 5 n=975 \\ &\text{ or, } n=\frac{975}{5}=195 \mathrm{~Hz} \end{aligned}
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