Q. In a resonance column cist and second resonance are obtained at depths 22.7 cm and 70.2 cm. The third resonance will be obtained at a depth
A) 117.7 cm
B) 92.9 cm
C) 115.5 cm
D) 113.5 cm
Explanation
(a) $l_{1} + x = \frac{\lambda}{4} = 22.7$;
$l_{2} + x = \frac{3\lambda}{4} = 70.2$; $l_{3} + x = \frac{5\lambda}{4}$
$x = \frac{l_{2} - 3l_{1}}{2} = \frac{70.2 - 68.1}{2} = \frac{2.1}{2} = 1.05\ cm$
$\frac{l_{3} + x}{l_{1} + x} = 5$
$l_{3} = 5l_{1} + 4x = 5 \times 22.7 + 4 \times 1.05 = 117.7\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.