Resonance Experiment for High School Students

Resonance experiment slides for NISER Open Day 2024

1. Resonance in Simple Pendulum and Water Column Open Day Demonstration in Physics-2024

2. Kinds of vibrations: Natural vibrations: A Tuning fork of some characteristic frequency f, is struck. This is a feature of shape and size of the object: known as natural frequency. Damped vibrations: Imagine the vibrating tuning fork, is dipped in water. The oscillation dies out pretty soon, due to drag forces in water. This is an example of damped vibrations. A Simple pendulum when made to oscillate, slowly comes to a rest, due to damping of the air. Forced Vibrations: If we hit a tuning fork attached to a table, the table vibrates with a frequency that is its own, and this is an example of natural frequency.

3. Natural Frequency of a pendulum: The characteristic time period of a simple pendulum is given as: However, we know: Our pendulum has a l=42.2 cm and assuming Natural frequency of pendulum comes out to be around 1.3 Hz This is too low to be verified experimentally using tuning forks. We will use indirect methods to show the phenomenon of Natural, Damped and Forced Oscillations. Specifically, we will discuss about Resonance ( as a special case of Forced Vibrations )  

4. Resonance in pendulum Resonance is a special case of Forced vibrations. When the frequency of externally applied periodic force on a body is equal to its natural frequency, the body vibrates with an increased amplitude. This phenomenon is known as resonance. We are demonstrating two setups in this section of experiment: Resonance using a set of tuning forks and a simple pendulum arrangement. Resonance in Air column by varying water level. ( )  

5. What are we supposed to see? For all the two cases, depending on the frequencies (f, f') of the tuning forks taken: Case 1: If f and f′ are far apart, a damping effect will occur. The oscillations will be smaller in the case of the pendulum, and the sound waves will be lesser in the case of the resonance tube. Case 2: If f and f′ are close together, resonance occurs, leading to constructive interference. This results in larger oscillations of the pendulum and enhanced sound waves in the resonance tube. Near Resonance or Beats: If f and f′ are slightly different, a phenomenon known as beats may occur. The amplitude of the oscillations will vary periodically, creating a distinct pattern of loud and soft sounds. Harmonics: The behaviour of the system can also be influenced by odd or even harmonics. Odd Harmonics: These frequencies can create distinct resonance patterns, leading to unique oscillation modes in the pendulum and varying sound characteristics in the resonance tube. Even Harmonics: These frequencies typically enhance the fundamental tone, resulting in smoother oscillations and more consistent sound waves. Hope you understand the theory behind the experiment better now !