The de Broglie wavelength is a fundamental concept in quantum mechanics that profoundly explains particle behavior at the quantum level. According to de Broglie hypothesis, particles like electrons, atoms, and molecules exhibit wave-like and particle-like properties.
This concept was introduced by French physicist Louis de Broglie in his doctoral thesis in 1924, revolutionizing our understanding of the nature of matter.
de Broglie Equation
A fundamental equation core to de Broglie hypothesis establishes the relationship between a particle’s wavelength and momentum. This equation is the cornerstone of quantum mechanics and sheds light on the wave-particle duality of matter. It revolutionizes our understanding of the behavior of particles at the quantum level. Here are some of the critical components of the de Broglie wavelength equation:
1. Planck’s Constant (h)
Central to this equation is Planck’s constant, denoted as “h.” Planck’s constant is a fundamental constant of nature, representing the smallest discrete unit of energy in quantum physics. Its value is approximately 6.626 x 10-34 Jˑs. Planck’s constant relates the momentum of a particle to its corresponding wavelength, bridging the gap between classical and quantum physics.
2. Particle Momentum (p)
The second critical component of the equation is the particle’s momentum, denoted as “p”. Momentum is a fundamental property of particles in classical physics, defined as the product of an object’s mass (m) and its velocity (v). In quantum mechanics, however, momentum takes on a slightly different form. It is the product of the particle’s mass and its velocity, adjusted by the de Broglie wavelength.
The mathematical formulation of de Broglie wavelength is
The SI unit of wavelength is meter or m. Another commonly used unit is nanometer or nm.
This equation tells us that the wavelength of a particle is inversely proportional to its mass and velocity. In other words, as the mass of a particle increases or its velocity decreases, its de Broglie wavelength becomes shorter, and it behaves more like a classical particle. Conversely, as the mass decreases or velocity increases, the wavelength becomes longer, and the particle exhibits wave-like behavior. To grasp the significance of this equation, let us consider the example of an electron.
de Broglie Wavelength of Electron
Electrons are incredibly tiny and possess a minimal mass. As a result, when they are accelerated, such as when they move around the nucleus of an atom, their velocities can become significant fractions of the speed of light, typically ~1%.
Consider an electron moving at 2 x 106 m/s. The rest mass of an electron is 9.1 x 10-31 kg. Therefore,
These short wavelengths are in the range of the sizes of atoms and molecules, which explains why electrons can exhibit wave-like interference patterns when interacting with matter, a phenomenon famously observed in the double-slit experiment.
Thermal de Broglie Wavelength
The thermal de Broglie wavelength is a concept that emerges when considering particles in a thermally agitated environment, typically at finite temperatures. In classical physics, particles in a gas undergo collision like billiard balls. However, particles exhibit wave-like behavior at the quantum level, including wave interference phenomenon. The thermal de Broglie wavelength considers the kinetic energy associated with particles due to their thermal motion.
At finite temperatures, particles within a system possess a range of energies described by the Maxwell-Boltzmann distribution. Some particles have relatively high energies, while others have low energies. The thermal de Broglie wavelength accounts for this distribution of kinetic energies. It helps to understand the statistical behavior of particles within a thermal ensemble.
Mathematical Expression
The thermal de Broglie wavelength (λth) is determined by incorporating both the mass (m) of the particle and its thermal kinetic energy (kT) into the de Broglie wavelength equation:
In 1924, French scientist Louis de Broglie (1892-1987) derived an equation that described the wave nature of any particle. Particularly, the wavelength (λ) of any moving object is given by: λ=hmv. In this equation, h is Planck's constant, m is the mass of the particle in kg, and v is the velocity of the particle in m/s ...
Wave character of matter has significance only for microscopic particles. de Broglie wavelength or wavelength of matter wave can be calculated using the following relation: λ=hmv where, 'm' and 'v' are the mass and velocity of the particle. de Broglie hypothesis suggested that electron waves were being diffracted by ...
The de Broglie equation is an equation used to describe the wave properties of matter, specifically, the wave nature of the electron: λ = h/mv, where λ is wavelength, h is Planck's constant, m is the mass of a particle, moving at a velocity v. de Broglie suggested that particles can exhibit properties of waves.
The de Broglie wavelength of a particle indicates the length scale at which wave-like properties are important for that particle. De Broglie wavelength is usually represented by the symbol λ or λdB.
Ans : Louis de Broglie hypothesised that every particle exhibits dual nature. Thus, the velocity of a particle will be equal to the group velocity of the corresponding wave. The magnitude of the group velocity is similar to the particle's speed.
The De Broglie hypothesis proposes that all matter exhibits wave-like properties and relates the observed wavelength of matter to its momentum. After Albert Einstein's photon theory became accepted, the question became whether this was true only for light or whether material objects also exhibited wave-like behavior.
The de Broglie hypothesis has various applications in our life. It helps in determining the probability of finding any particle in the configuration space. It is also used in the construction of an electron microscope. These are popularly used in biology labs to study microscopic organisms like bacteria, viruses etc.
According to De Broglie's theory of matter waves, each particle of matter with linear momentum is also a wave. The amount of a particle's linear momentum is inversely proportional to the wavelength of a matter wave associated with that particle.
The wavelength λ = h/p is called the de Broglie wavelength, and the relations λ = h/p and f = E/h are called the de Broglie relations. These are the same relations we have for the photon, but for particle E = (1/2)mv2 = p2/(2m), so E = ћ2k2/(2m), λ = h/√(2mE).
The De Broglie equation states that every particle that moves can sometimes act as a wave, and sometimes as a particle. The wave which is associated with the particles that are moving are known as the matter-wave, and also as the De Broglie wave.
De Broglie concluded that most particles are too heavy to observe their wave properties. When the mass of an object is very small, however, the wave properties can be detected experimentally. De Broglie predicted that the mass of an electron was small enough to exhibit the properties of both particles and waves.
The De Broglie equation states that every particle that moves can sometimes act as a wave, and sometimes as a particle. The wave which is associated with the particles that are moving are known as the matter-wave, and also as the De Broglie wave. The wavelength is known as the de Broglie wavelength.
Hence, the de Broglie wavelength, λ=hp=hmv=h√2mqV. Write the expression for the Broglie wavelength associated with a charged particle having charge 'q' and mass 'm', when it is accelerated by a potential V.
Introduction: My name is Geoffrey Lueilwitz, I am a zealous, encouraging, sparkling, enchanting, graceful, faithful, nice person who loves writing and wants to share my knowledge and understanding with you.
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