Franck–Hertz Experiment


Introduction

The Franck–Hertz experiment, conducted by James Franck and Gustav Hertz in 1914, was a pivotal moment in the history of physics. This experiment was the first to provide clear evidence of the quantum nature of atoms.

Franck and Hertz designed a vacuum tube to study the behaviour of energetic electrons passing through a thin vapour of mercury atoms. They discovered that when an electron collided with a mercury atom, it lost a specific amount of energy—4.9 electron volts (eV). *((In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt in vacuum. SI, this sets 1 eV equal to the exact value 1.602176634×10−19 J)) This amount of energy corresponds to decelerating the electron from a speed of about 1.3 million meters per second to zero. Faster electrons didn’t slow down completely but lost exactly the same amount of kinetic energy, while slower electrons bounced off mercury atoms without significant energy loss.

These results were consistent with the Bohr model of the atom, which had been proposed by Niels Bohr the previous year. According to this model, electrons inside an atom occupy specific energy levels. Before a collision, an electron inside a mercury atom occupies its lowest energy level. After the collision, the electron moves to a higher energy level, absorbing 4.9 eV of energy. This means that electrons can only be bound to the atom with certain fixed amounts of energy, a revolutionary idea at the time.

In a follow-up paper in May 1914, Franck and Hertz reported that the mercury atoms, after absorbing energy from collisions, emitted ultraviolet light. The wavelength of this light corresponded exactly to the 4.9 eV of energy lost by the electrons, confirming Bohr's predictions about energy and wavelength.
Impact

These findings confirmed the quantization of energy levels in atoms, an essential concept in quantum mechanics. The experiment's elegance led Albert Einstein to remark, "It's so lovely it makes you cry." Franck and Hertz were awarded the Nobel Prize in Physics in 1925 for their discovery.

This experiment illustrated how the quantum world works, in the way of modern atomic theory. It showed that scientific inquiry could reveal the hidden structures and principles governing the universe, helping to bridge the gap between theory and observable reality.

vacuum tube used for the Franck–Hertz experiment in instructional laboratories. There is a droplet of mercury inside the tube, although it is not visible in the photograph. C – cathode assembly; the cathode itself is hot, and glows orange. It emits electrons which pass through the metal mesh grid (G) and are collected as an electric current by the anode (A).



Watch a YouTube video explaining: https://youtu.be/MCJl3-pHGuU?si=V0CXYZaL8pAsmuyB





Technological Advancement


The principles discovered in the Franck–Hertz experiment are fundamental to our understanding of quantum mechanics, which underpins much of modern technology.
  1. Semiconductors: The technology in your computer and smartphone relies on quantum mechanics to function.
  2. Medical Imaging: Techniques like MRI and PET scans are based on quantum principles.
  3. Lasers: Used in everything from CD players to cutting-edge medical treatments, lasers operate on quantum mechanics.
  4. Quantum Computing: This emerging field aims to revolutionize computing power by leveraging the principles of quantum mechanics.

What  we witness in vintage electronics - Vacuum Tube


The vacuum tube in the Franck–Hertz experiment is similar to the ones used in old tube radios but with a different purpose.



Vacuum Tubes in Radios:

  • Function: Amplifying signals and switching in early electronics.
  • Construction: Glass tubes with electrodes that control the flow of electrons.

Franck–Hertz Experiment Tubes:

  • Function: Studying electron collisions with mercury atoms to understand quantized energy levels.
  • Construction: Similar glass tubes, but filled with a thin vapour of mercury for the specific purpose of observing energy changes during electron collisions.

How quantum state evolves over time: understanding the behaviour of particles at the quantum level.


  • i is the imaginary unit.
  • ℏ (h-bar) is the reduced Planck's constant.
  • ψ (psi) is the wave function of the quantum system.
  • H^ is the Hamiltonian operator, representing the total energy of the system (kinetic + potential energy).


Imagine a particle confined in a one-dimensional box with perfectly rigid walls. The Schrödinger equation helps determine the allowed energy levels and the corresponding wave functions of the particle.

By solving this equation, we find that the energy levels are quantized, meaning the particle can only possess specific energy values. This is a direct consequence of the wave nature of particles and their confinement.

Comments

Post a Comment

Popular posts from this blog

Interplay of Art, Mind and Reality

Image
 Introduction  The interplay of art, mind, and reality is a fascinating dance that reflects how humans interpret, shape, and transcend their existence. The mind of an artist holds a profound secret, translating transcendent mental images into art. Art, in essence, is a reflection of the artist's mind. Human anatomy, as an example, is a highly sophisticated biological science. But what if I were to say that the human mind and the entirety of physical nature are the true sciences that hold every secret of the universe? Spiritual beliefs and many religions suggest that human consciousness has extraordinary abilities, often limited by formal education—"the basics we learn in school"—and by what society teaches us to accept. For instance, if you ask a student, “What is 2+2? ” they would simply answer, “4.” If you then ask, “Why is it 4 and not something else?” they might struggle to explain. This is because we are taught that 2+2 equals 4 without question or deeper understa...
Read more

The Invention of Blue LED

Image
 Introduction  Light-emitting diodes (LEDs) have brought about a revolution in how we illuminate our world and display information. These fascinating semiconductor devices emit light when an electric current flows through them. The magic happens when electrons in the semiconductor recombine with electron holes , releasing energy in the form of photons . The color of the light emitted depends on the energy required for electrons to cross the semiconductor's band gap. Using multiple semiconductors or a layer of light-emitting phosphor , we can even create white light.  Electronic symbol Parts of a conventional LED. The flat bottom surfaces of the anvil and post embedded inside the epoxy act as anchors, to prevent the conductors from being forcefully pulled out via mechanical strain or vibration. The story of LEDs dates back to 1962 when they first appeared as practical electronic components, emitting low-intensity infrared (IR) light. These IR LEDs became essential in remo...
Read more

Science of Shilpa Shastra

Image
Introduction  Shilpa Shastra, often referred to as the " Science of Arts and Crafts ," is an ancient Indian treatise that seamlessly combines aesthetics, technical expertise, and spirituality. Rooted in profound philosophy, this text serves as a comprehensive guide to sculpture, architecture, painting, and various crafts, with its principles deeply embedded in cultural and religious traditions. It lays down meticulous design standards, emphasizing harmony, proportions, and symbolic meanings, particularly in Hindu temple architecture and iconography.  Beyond mere craftsmanship, Shilpa Shastra offers insights into the connection between creativity and divinity, introducing the 64 external arts (Bahya-kala) and 64 internal arts (Abhyantara-kala) as part of its extensive knowledge repository. From the design of awe-inspiring temples to intricate sculptures that breathe life into myths, this ancient science represents the pinnacle of artistic and architectural innovation in India...
Read more