Question

A source '$s$' is emitting waves, which travels through a tube of given shape. The detector '$D$ ' detects constructive interference of certain frequencies. If speed of wave is $v$ and $n$ is an integer then those frequencies are

• A. $\frac{na}{v}$
• B. $\frac{v}{na}$
• C. $\frac{nv}{a}$
• D. $\frac{a}{nv}$

Answer 1

The correct option is C $\frac{nv}{a}$

From the given figure we can say that
$\Delta x=3a-2a=a=n\lambda$
Also, for constructive interfernce.
$f=\frac{v}{\lambda }=\frac{v}{\frac{a}{n}}=\frac{nv}{a}$