List of Modern Physics Topics
Modern physics chapters cover the following topics:
Atomic Theory & Atomic Model
Till the end of the nineteenth century, it was believed that atoms could be divided into smaller units, but now we know that subatomic particles are present in atoms. Atomic theories define that matter is composed of atoms. Neutrons, protons, and electrons are the basic units of an atom. Protons carry a positive charge, electrons carry a negative charge, and neutrons do not carry any charge.
An atomic model is a theoretical representation to describe the structure of an atom. Scientists gave different atomic models. J.J.Thomson gave the Plum pudding model. The basic idea of this model was that the neutrons of atoms are distributed like pudding and electrons are suspended throughout the pudding like the plums in a pudding.
Rutherford’s atomic model suggested that electrons revolve in the orbits around the nucleus. The atomic nucleus contains a positive charge. The total charge on an atom is zero, so the number of electrons must equal the number of protons.
Bohr’s model, given by Neil Bohr in 1913, proposed that the central part of an atom’s nucleus carries positive charges. Electrons revolve around the nucleus (positive charge) in circular paths called orbits. Centripetal force is required for the circular motion of electrons. Each orbit has a fixed amount of energy, and when an electron revolves around a nucleus in orbit, it neither loses nor gains energy. He labelled energy levels as K, L, M, N, and so on.
Quantum theory defined the atomic model and replaced orbits of electrons with discrete energy levels. Defined electron as wave-particle by a wave function with separate, individual energy levels. On losing and gaining energy, electrons transit between the energy levels.
Black Body Radiation
The thermal electromagnetic radiation released by the blackbody when the body is in thermal equilibrium along with its surroundings is called blackbody radiation. As shown in the figure, classical theory explains blackbody radiation for higher wavelengths for low wavelength black body radiation is calculated using quantum laws.
Rutherford Experiment
Rutherford’s experiment was conducted in 1911 using a gold foil and alpha particle scattering. This experiment came out with different hypotheses that an atom has primarily empty spaces, and the positive charge is concentrated at its core, called the nucleus. This model is also called the nuclear model.
Learn about alpha decay.
Frank-Hertz experiment
Frank-Hertz experiment was conducted in 1914. This was the first experiment that clearly showed the quantum nature of atoms. This experiment’s main aim was to show an atom’s quantized energy levels according to Bohr’s model. The Frank-Hertz experiment changed the world’s view of the structure of an atom.
Michelson- Morley experiment
In 1864, it was proved that light is an electromagnetic wave and assumed that it travels through ether medium. So the Michelson-Morley experiment was conducted to detect the velocity of light in an ether medium. He used an interferometer (optical device) to compare the path lengths of light waves travelling in perpendicular directions. He concluded that there is no difference in the speed of light while travelling through the ether.
Photoelectric Effect
This effect is the emission of electrons from a metal surface when light (photons) are made incident on it. The emitted electrons are known as photoelectrons.
The outcomes of this experiment were-
- All emitted electrons have different energies.
- The energy of a photoelectron depends upon the incident light and the surface area of metal.
- There is a minimum frequency below which electrons cannot emit from the metal surface.
- The electrons are discharged from the metal surface simultaneously and depend upon light intensity.
Stern-Gerlach Experiment
In this experiment, a beam of particles was sent through the inhomogeneous magnetic field to observe the deflection of particles. This experiment showed that particles possess intrinsic angular momentum, which takes only specific quantized values. Moreover, the intrinsic angular momentum was closely related to the classically spinning object’s angular momentum.
Stern-Gerlach’s experiment’s other significant result was that only one component of a particle’s spin is measured at a time. So, for example, if we are measuring the spin of a particle along the z-axis, then we cannot measure momentum on the x and y-axis simultaneously.
Wave-Particle Duality
In 1923, de Broglie proposed that light has a dual nature. It acts both as a particle and a wave. Diffraction and interference show the wave nature of the light, while the photoelectric effect shows the particle nature of light, i.e., light is made up of photons.
Quantum Mechanics
Quantum mechanics is the branch of quantum physics. It explains the fundamental theory, which describes the physical properties of subatomic and atomic particles. Further, it explains the properties of fundamental particles (gluons, quarks, neutrons, electrons, protons, etc.). The Quantum effect is hard to notice with large bodies. Classical mechanics is applied.
