Question

In a resonace air column experiment, first and second resonances are obtained at lengths of air columns $l_1$ and $l_2$, the third resonance will be obtained at a length of

• A. $2l_2-l_1$
• B. $l_2-2l+1$
• C. $l_2-l_1$
• D. $3l_2-l_1$

Answer 1

Answer: (A)

$2l_2-l_1$

Answer 2

$l_1 +e = \frac{\lambda}{4}$ $\Rightarrow$ (1) $l_2 + e = \frac{3 \lambda}{4}$ $\Rightarrow$ (2) from (1) , (2) sub e, $\lambda$ in $l_3 + e = \frac{5 \lambda}{4}$