IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

# Reflection of Sound

## Objective

To demonstrate laws of reflection for the sound

## Introduction

The students often remember laws of reflection without understanding them.

## Procedure

Take two long, identical tubes and place them on a table near a wall. Ask your friend to speak softly into one tube while you use the other tube to listen. You will find that you hear your friend's voice best when the tubes make equal angles with the wall, i.e., when $$\angle i=\angle r$$. Also, if you lift your tube off the table, you will not be able to hear your friend's voice clearly. This is because your tube, the incident sound and the normal are no longer in the same plane.

Repeat the experiment by placing flat objects of different materials (steel and plastic trays, a cardboard, a tray draped with cloth, etc.) against the wall. You will find that hard surfaces reflect sound better than soft ones.

## Note

This experiment is given in textbooks but we could not observe what the experiment claims.