A summary of five experiments conducted during a summer school.
BY IKBAL AHMED & DEBDUTTA PAUL
Science has always been a realm of exploration and wonder, captivating those who dare to explore its mysteries. Unfortunately, the field of physics has been traditionally dominated by men. Recognising the need for inclusivity and diversity in the scientific community, the International Centre for Theoretical Sciences (ICTS) at the Tata Institute of Fundamental Research (TIFR) organised a Summer School for Women in Physics between the 29th of May and the 9th of June, 2023.
The program aimed to inspire undergraduate women students. There, we demonstrated physical concepts with interactive experiments. Let’s embark on a journey through some of the experiments.
Experiment 1: Harnessing the Power of Electricity With Van de Graaff Generator
Can things move without any physical contact? The participants got an opportunity to explore the Van de Graaff generator, which provided a way to demonstrate how electric charges move and behave.
The triboelectric series ranks different materials based on how eagerly they exchange electrons as they come into contact. While certain materials, like rubber, readily grab electrons, others, like wool, are more willing to give them away.
Consider rubbing rubber against a woollen cloth. An exchange of electrons occurs. The rubber grabs electrons from the wool, which is happy to provide them. As a result, the wool acquires a net positive charge, and the rubber acquires a net negative charge.
The in-house Van de Graaff generator built at ICTS includes a moving rubber belt and a charged metal dome, a Diet Coke can or a ball wrapped around with aluminium foil, sitting on top. The rubber belt is located at the centre of this machine and dances across two rollers at the top and wrapped wool at the bottom. The rollers consist of common household insulating pipes called CPVC pipes.
As the rubber belt rubs against the wool, the belt becomes negatively charged, and the wool becomes positively charged. The rubber rolls to the top, where a metal brush connected to the metal dome collects the negative charges and distributes them across the dome’s outer surface. A reverse process occurs between the top roller and the rubber belt, increasing the amount of charge in the generator.
As the participants learned, electricity can give objects life! Silk ribbons attached to the dome swirled in the intangible embrace of electrical charge while puffed rice was flung into the air, defying gravity.
Experiment 2: Unveiling the Beauty of Soap Films
Soap bubbles fascinate us beyond the delight of childhood play. The school participants got a glimpse of the intriguing world of soap films.
We immersed a rectangular frame in a 10% mix of dish soap and water to create a soap film. Then, we placed a loop of thread on the soap film. By poking the film within the thread with a dry stick, we disrupted it. The film within the thread ruptured, and the distorted thread transformed into a circle.
Soap films are formed due to surface tension, which is the attractive force between molecules at the surface of a liquid. The properties of a film come from the arrangement of soap molecules that hold water between them.
When we place an irregularly shaped thread on the soap film and break the film within it, the surface tension forces the connected film to minimise its surface energy. Since the surface energy is proportional to the surface area, it minimises the area of the connected film. That is, the area of the hole is maximised, which happens when it becomes a circle.
The principle of minimal surface area has diverse applications in fluid mechanics, mathematics, and even architecture.
Experiment 3: Swinging Science: Unveiling Kapitza’s Pendulum
Kapitza’s pendulum helped us visualise a dance between gravitation and vibrations. Our setup involved a combination of elements: a vibration generator, a signal generator, a guitar string, a hook, and a needle. With these, we could achieve a slender needle delicately poised in mid-air.
We connected one end of the guitar string to the vibration generator and attached the other end to a hook. We connected the vibration generator to the signal generator, which creates an electrical pulse at a particular frequency, which we can control. The vibration generator creates a physical vibration of the guitar string at the frequency of the signal generator. Thus, we could vary the frequency of the string’s vibration.
We slid the needle around the string. So, when the string vibrates, the needle’s pivot point vibrates at the same frequency.
When we set the frequency of the signal generator to 33.5 hertz, or those 33.5 vibrations per second, and varied the tension of the string manually at the open end, the needle stood up on the string in an upright position.
This phenomenon happens due to the nonlinear vibrations of the pendulum, driven by the vibration of the pivot point. This combined vibration gives rise to an equilibrium for the needle at this frequency.
The resulting dynamic equilibrium effectively counteracts gravity, and the needle can remain upright in an inverted position. The pendulum experiment showcases the ability of controlled vibrations to overcome gravitational forces and achieve a state of equilibrium.
Experiment 4: Discovering the Fascinating World of Sound Waves
Sound waves can captivate us in diverse ways. The Doppler effect explains the change in sound’s frequency as a sound’s source or its observer move relative to each other. In this experiment, a participant used a buzzer attached to a string and rotated it in a circle, while her peer used the mobile application phyphox to record the variation in frequency.
As the buzzer attached to the string is rotated, the sound waves emitted by the buzzer undergo deformation. When the buzzer approaches the observer, the waves get compressed, which increases their frequency. When the buzzer moves away from the observer, the waves get stretched, which decreases their frequency.
Experiment 5: Chladni plates
In another activity, a participant spread rava (a form of semolina) particles on a horizontal metal plate mounted on a stand. Then, she used a violin bow to vibrate the plate. After a few strokes, the rava particles formed patterns.
Here, the bow’s strokes create sound waves that vibrate the plate. These vibration patterns, known as Chladni figures, depend on the plate’s geometry and the vibration frequency.
When the plate is vibrated at a specific frequency, standing waves are created. At certain places, known as nodes, the plate doesn’t move. At these points, the particles of rava stay put, forming visible patterns. The segments of the plate that are vibrating vigorously, called antinodes, push the particles away.
So, the patterns formed illustrate how the plate vibrates and are related to the frequency and shape of the plate. When the frequency is changed, the pattern changes, demonstrating the different ways a plate can vibrate. These are called its different vibrational modes.
The formation of different intricate patterns demonstrates the diverse frequencies at which the system can resonate. The study of these patterns and the conditions facilitating them are fundamental aspects of the field of acoustics. Scientists use Chladni plates in acoustic research to visually study this wave phenomenon.
The Summer School for Women in Physics at ICTS-TIFR provided a platform for women undergraduate students to delve into the captivating world of physics. Through interactive experiments, the participants discovered the beauty, relevance, and practical applications of scientific concepts. ICTS strives to create a future where every woman feels empowered to explore the wonders of the universe.
Resources:
- Reading materials by Ikbal Ahmed
- Image and video gallery
Spoorthi AS and Sharmada Iyer attended the Summer School for Women in Physics held at ICTS between the 29th of May and the 9th of June, 2023.
The authors thank Professor Joseph Samuel for support.