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

# Phase Difference Between Oscillations

## Introduction

Wave motion is conceptually much more difficult to understand than the particle motion. On top of it one needs two waves and their combined effect for interference etc. The concept of phase and phase difference is most important in any wave phenomena. This activity is to give a physical feel of what are phases and phase differences.

## Apparatus

Two simple pendulums with equal length

## Procedure

1. Oscillate a simple pendulum. Call one extreme position as phase-0. Let it be the left extreme. Identify the phases at different times of oscillation.
• What is the phase when the bob is at the mean position and going towards right?
• What is the phase when the bob is at the mean position and going towards left?
• What is the phase when the bob is at the right extreme?
2. Hold the bob by hand and take to different positions. Think of the phase.
3. Now keep the two pendulums side by side. Pull the two bobs on the same side by the same amount and leave simultaneously. What is the phase difference between these oscillations?
4. Pull the two bobs on the same sides by different amounts and leave simultaneously. What is the phase difference between these oscillations?
5. Pull the two bobs on opposite sides and leave simultaneously. What is the phase difference between these oscillations?
6. Oscillate two bobs so that their phase difference is $$\pi/2$$.