Answer:
Brownian motion: Einstein showed that the random motion of particles suspended in a liquid could be explained by the collision of these particles with individual atoms or molecules. This provided experimental evidence for the existence of atoms and molecules.
Photoelectric effect: Einstein demonstrated that the concept that light is quantized—that is, that it arrives in distinct packets of energy known as photons—can be used to explain the photoelectric phenomenon. This work led to the development of quantum mechanics, which is the foundation of our modern understanding of atoms.
Bohr model of the atom: Einstein proposed a model of the atom in which electrons orbit the nucleus in fixed energy levels. This model is known as the Bohr model of the atom.
Step-by-step explanation:
Brownian motion: Brownian motion is the random movement of microscopic particles suspended in a fluid. Robert Brown made the initial observation in 1827, and it remained a mystery for a long time. Einstein was able to explain Brownian motion in 1905 by showing that it was caused by the collisions of the particles with individual atoms or molecules of the fluid. This was a major breakthrough, as it provided experimental evidence for the existence of atoms and molecules. Einstein's explanation of Brownian motion was based on the idea that atoms and molecules are constantly in motion. When a particle is suspended in a fluid, it is constantly being bombarded by the atoms or molecules of the fluid. The particle is forced to travel randomly as a result of this bombardment. The size of the particle and the temperature of the fluid determine the speed and direction of the particle's motion.
Photoelectric effect: Einstein showed that the photoelectric effect could be explained by the idea that light is quantized, meaning that it comes in discrete packets of energy called photons. This work led to the development of quantum mechanics, which is the foundation of our modern understanding of atoms. When a metal is exposed to light, it emits electrons, which is known as the photoelectric effect. Einstein showed that this effect could be explained by the idea that light is quantized. He proposed that light is not a continuous wave, but rather a stream of particles called photons. Each photon has a specific amount of energy, and when a photon hits an electron in a metal, it can give the electron enough energy to escape from the metal.
Bohr model of the atom: The Bohr model of the atom was proposed by Niels Bohr in 1913. This model was based on Einstein's work on the photoelectric effect and on the work of other physicists, such as Max Planck and Louis de Broglie. The Bohr model of the atom is a simple model that provides a good explanation of the spectra of atoms. The Bohr model of the atom states that electrons can only orbit the nucleus in certain fixed energy levels. These energy levels are quantized, meaning that they can only have certain values. When an electron moves from one energy level to another, it emits or absorbs a photon of light. The frequency of the photon is determined by the difference in energy between the two energy levels.