Question

An organ pipe open at both ends contains
(A) Longitudinal stationary waves
(B) Longitudinal progressive waves
(C) Transverse stationary waves
(D) Transverse progressive waves

Answer 1

Hint: Sounds travels in fluids (liquids and gases) as longitudinal waves. Musical instruments create loud sound by the standing waves in their column.

Complete step by step answer
When a musical instrument (especially wind instrument) such as an organ pipe is blown, they create standing waves in their column, which actually set other air molecules into vibrations and the waves are carried into our ears to be perceived.
Generally, there two types of those columns made and two different types of standing waves are generated in them. One column or pipe closes at one end but open at the other (called a closed pipe) and another is open at both ends, called an open pipe.
In a closed pipe – when the wave enters through one of the ends, it gets reflected from the other end, and creates a sound wave of the same frequency but phase shift of 180 headed back in the opposite direction as the incident wave. Standing waves possess what is called nodes and antinodes. Nodes are the point of minimum displacement of the particles of the wave while the antinodes are the point of maximum displacement. For a closed pipe, the node is said to be at the end, i.e. the point of reflection.
In an open pipe acts similarly, standing waves are formed but at the end of the pipe is always the antinode. All sound waves travelling in fluids are always longitudinal.

Hence, the correct answer is A.

Note
Although, we said the standing waves produced by an open pipe (pipe open at both ends) like our pipe organ, has an antinode at the end, in actuality, this is not what happens exactly through. The antinode is actually a little beyond the end of the pipe in practical cases.