Introduction When waves pass through a narrow gap, they spread out. This spreading out is called diffraction. Diffraction is defined as the spreading of a wave into regions where it would not be seen if it moved only in straight lines after passing through a narrow slit or past an edge. Diffraction of a light … Read more

Superposition Of Waves

Introduction If two or more waves collide, they are said to interfere. Interference is a property of waves. In this article, properties of the resultant waves created in interference is explained. A. Superposition of waves The principle of superposition states that when two or more waves meet at a point, the resultant displacement at that … Read more

Collisions Of Electrons With Atoms

Introduction An electron is a subatomic particle with finite mass and negative electric charge. Electron orbits the nucleus of an atom. When an external electron collides with an atom, the energy of the moving electron gets transferred to the atom. In this article, collision of electron with atom and terms associated with the collision are … Read more

Wave-Particle Duality

Introduction Light waves can behave like particles (photons) and waves. This phenomena is called the wave-particle nature of light or wave-particle duality. In this article, how a light wave behaves like a particle and a wave are explained. A. Diffraction When a beam of X-rays of a single wavelength is directed at a thin metal … Read more

Energy Levels & Photon Emission

Introduction When white light from a tungsten filament is passed through a prism, the light is dispersed into its component colours, as illustrated in Figure 1. The band of different colours is called a continuous spectrum. Figure 1: Continuous Spectrum A. Emission Spectrum In the experiment shown in Figure 1, the resultant colour and wavelength … Read more

Photoelectric Effect

Introduction Protons, neutrons and electrons that move around the nucleus constitute an atom, as illustrated in Figure 1. Some of the electrons in a metal are free to move around. These electrons are called free electrons. To remove these free electrons from a metal, energy is required because they are held in the metal by … Read more

Particle & Radiation

Introduction The atoms of all elements are made up of three particles called protons, neutrons and electrons. To understand the fundamental forces existing in the universe, it is important to learn about particles, subatomic particles, and their properties. Radioactive decay of a nucleus and the nature of particles emitted in the decay are helpful in … Read more

Quarks & Anti-Quarks

Introduction In the classification of subatomic particles, as illustrated in Figure 1, Hadrons (Mesons and Baryons) are made up of three smaller particles called quarks. The types of quark are: up (u), down (d) and strange (s). These three types of quarks are also called the three flavours of quark. The combination of these quarks … Read more

Stable & Unstable Nuclei

Introduction An atom contains an equal number of positively charged protons and negatively charged electrons and their charges balance. However, the nucleus contains positively charged protons, which are closely packed together in a very small volume. According to the laws of physics, the protons exert strong repulsive forces on each other. This implies that there … Read more

Particle, Antiparticle & Photons

Introduction Every particle has an antiparticle, according to the standard model for describing fundamental particles and interactions. For example, the positron is the antiparticle of the electron. A positron has identical mass, but has a positive charge. If an electron encounters a positron, they annihilate with the transformation of their mass-energies into two gamma rays. … Read more