An open organ pipe and a closed organ pipe have the frequency of their second overtone identical. The ratio of length of closed pipe to that of open pipe is (Neglect end correction)

A wave is travelling in the negative x direction having displacement 3 cm along Y direction, wavelength $2 \pi \mathrm{~m}$ and frequency $\left(\frac{1}{2 \pi}\right) \mathrm{Hz}$ is represented as ( $t=$ time)

A passenger is sitting in a train which is moving fast. The engine blows a whistle of frequency ' n '. If the apparent frequency of sound heard by the passenger is $n^1$ then

Two points on a travelling wave having frequency 500 Hz and velocity $300 \mathrm{~m} / \mathrm{s}$ are $30^{\circ}$ out of phase, then the minimum distance between the two points is