Question

In a Kundt’s experiment, the heaps of lycopodium powder are collected at $20{\text{cm}}$ separations. The frequency of tuning fork used is
A) $\left( {\text{A}} \right)660{\text{Hz}}$
B) $\left( {\text{B}} \right)825{\text{Hz}}$
C) $\left( {\text{C}} \right)775{\text{Hz}}$
D) $\left( {\text{D}} \right)915{\text{Hz}}$

Answer 1

Hint:Kundt’s tube: It is made up of a transparent horizontal pipe-like instrument that contains a small amount of a fine powder such as cork dust, talc, or lycopodium.

At one end of the tube, there is a source of sound at a single frequency (a pure tone).
A metal rod resonator that caused vibration or 'ring' by rubbing the rods, but nowadays in modern demonstrations usually use a loudspeaker attached to a signal generator.

Formula used:
${\text{f = }}\dfrac{{\text{c}}}{\lambda }$, here f = frequency of the sound wave,
c= speed of the light source,
$\lambda $= wavelength of the sound wave

Complete step-by-step solution:
In 1866, German physicist August Kundt invented Kundt's tube as an experimental acoustical instrument.
It is used to measure the speed of sound in a gas or a solid rod.
The experiment is still used due to its ability to demonstrate longitudinal waves in a gas (which can often be difficult to visualize).
Nowadays, it is used for demonstrating standing waves and acoustical forces.
It is given that ${\text{d = 20cm}}$,
Here d= separation of the heaps
Therefore, we can write that, ${\text{d = }}\dfrac{\lambda }{2} = 20{\text{cm}}$
From the above equation, we get the value as $\lambda = 40{\text{cm}}$
Then, we can find the value of frequency, ${\text{f = }}\dfrac{{\text{c}}}{\lambda }$
Putting the values we get,
$ = \frac{{330}}{{0.4}}$
Let us divide the term we get,
$ = 825{\text{Hz}}$

Hence the correct option is (B)

Note:- Lycopodium powder is yellow-tan dust-like powder.
-Lycopodium powder consists of dry spores of club moss plants, ferns.
-When lycopodium powder is mixed with air, the spores formed are highly flammable.
-Kundt’s tube is used to find the wavelength of sound with the cork-powder method.