Two sitar strings, \(A\)  and \(B,\)  playing the note \('Dha'\)  are slightly out of tune and produce beats and frequency  \(5\,Hz.\)  The tension of the string \(B\) is slightly increased and the beat frequency is found to decrease by  \(3\,Hz\) . If the frequency of \(A\) is \(425\,Hz,\)  the original frequency of \(B\) is  ... \(Hz\)

Beat frequency \(x=5\) \(Hz\) which is decreasing \((5 \rightarrow 3)\) after increasing the tension of the string \(B\).

Also tension of string \(\mathrm{B}\) increasing so

\(\mathrm{n}_{\mathrm{B}} \uparrow(\because \mathrm{n} \propto \sqrt{\mathrm{T}})\)

Hence \(\quad \mathrm{n}_{\mathrm{A}}-\mathrm{n}_{\mathrm{B}} \uparrow=x \downarrow \longrightarrow\) correct

\(\mathrm{n}_{\mathrm{B}} \uparrow-\mathrm{n}_{\mathrm{A}}=\mathrm{x} \downarrow  \longrightarrow \text { incorrect }\)

\(\therefore \mathrm{n}_{\mathrm{B}}=\mathrm{n}_{\mathrm{A}}-\mathrm{x}=425-5=420 \mathrm{Hz}\)