Two open organ pipes of fundamental frequencies $\mathrm{n}_{1}$ and $\mathrm{n}_{2}$ are joined in series.…

Two open organ pipes of fundamental frequencies $\mathrm{n}_{1}$ and $\mathrm{n}_{2}$ are joined in series. The fundamental frequency of the new pipe is
  1. $\mathrm{n}_{1}-\mathrm{n}_{2}$
  2. $\frac{n_{1} n_{2}}{\left(n_{1}+n_{2}\right)}$
  3. $\frac{1}{n_{1} n_{2}}$
  4. $\frac{n_{1}+n_{2}}{n_{1} n_{2}}$

Solution

$\mathfrak{n}=\frac{\mathrm{V}}{2 \ell_{1}} \quad \therefore \quad \ell_{1}=\frac{\mathrm{V}}{2 \mathrm{n}_{1}}$ $\mathfrak{n}_{2}=\frac{\mathrm{V}}{2 \ell_{2}} \quad \therefore \quad \ell_{2}=\frac{\mathrm{V}}{2 \mathrm{n}_{2}}$ $\mathfrak{n}=\frac{\mathrm{V}}{2 \ell} \quad \therefore \quad \ell=\frac{\mathrm{V}}{2 \mathrm{n}}$ $\ell=\ell_{1}+\ell_{2}$ $\frac{\mathrm{V}}{2 \mathrm{n}}=\frac{\mathrm{V}}{2 \mathrm{n}_{1}}+\frac{\mathrm{V}}{2 \mathrm{n}_{2}}$ $\therefore \frac{1}{\mathrm{n}}=\frac{1}{\mathrm{n}_{1}}+\frac{1}{\mathrm{n}_{2}}$ $\therefore \mathrm{n}=\frac{\mathrm{n}_{1} \mathrm{n}_{2}}{\mathrm{n}_{1}+\mathrm{n}_{2}}$

Asked in: MHT CET 2020 (14 Oct Shift 1)

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