Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 11
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A Sonometer Wire Supports a 4 Kg Load and Vibrates in Fundamental Mode with a Tuning Fork of Frequency 416. Hz. the Length of the Wire Between the Bridges is Now Doubled. - Physics


A sonometer wire supports a 4 kg load and vibrates in fundamental mode with a tuning fork of frequency 416. Hz. The length of the wire between the bridges is now doubled. In order to maintain fundamental mode, the load should be changed to


  • 1 kg

  • 2 kg

  • 8 kg

  • 16 kg.

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16 kg

According to the relation of the fundamental frequency of a string
\[\nu = \frac{1}{2l}\sqrt{\frac{F}{\mu}}\]
where l is the length of the string
           is the tension
           μ is the linear mass density of the string
We know that ν1 = 416 Hz, l1 = l and l2 = 2l.
Also, m1 = 4 kg and m2 = ? 
\[\nu_1 = \frac{1}{2 l_1}\sqrt{\frac{m_1 g}{\mu}}..................  (1)\]
\[\nu_2  = \frac{1}{2 l_2}\sqrt{\frac{m_2 g}{\mu}}                (2)\]
So, in order to maintain the same fundamental mode
\[\nu_1  =  \nu_2\]
squaring both sides of equations (1) and (2) and then equating

\[\frac{1}{4 l^2}\frac{4g}{\mu}   =   \frac{1}{16 l^2}\frac{m_2 g}{\mu}\] 

\[ \Rightarrow  m_2  = 16  kg\] 

  Is there an error in this question or solution?
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HC Verma Class 11, 12 Concepts of Physics 1
Chapter 15 Wave Motion and Waves on a String
MCQ | Q 22 | Page 323
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