Band Theory of Solids Energy Band theory is used to study the behaviour of solids as conductors (metals), insulators and semiconductors. Electrons of each isolated atom have discrete energy levels. When two similar atoms are brought closer, then there is an interaction between the valence electrons of these two. This interaction causes a splitting of … Read more
Emission of electrons At room temperature the free electrons move randomly within the conductor, but they don’t leave the surface of the conductor due to attraction of positive charges. Some external energy is required to emit electrons from a metal surface.The minimum energy required to emit the electrons which are just on the surface of … Read more
Physical Quantities All the quantities in terms of which laws of physics are described, and whose measurement is necessary are called physical quantities. Units The standard scale which is used to measure value of any physical quantity is called units. Fundamental Units Those physical quantities which are independent to each other are called fundamental quantities … Read more
Nucleus Positive charge of an atom is concentrated in the nucleus due to positively charged particles known as protons. Proton is a positively charged particle. The number of protons in the nucleus is called atomic number (Z) of the atom. The sum of the number of protons (Z) and the number of neutrons is called … Read more
Thomson’s Atom Model According to Thomson, an atom is a sphere of positive charges of uniform density of about 10-10 m diameter in which negative charges i.e. electrons are embedded like plums in the pudding. Thomson’s model could not explain the presence of discrete spectral lines emitted by hydrogen and other atoms. Hence efforts were … Read more
In 1895, Wilhelm Konard Roentgen discovered X-rays while working with a discharge tube. X means unknown. X-rays are electromagnetic radiation of very short wavelength and high energy which are emitted when fast moving electrons or cathode rays strike a target of high atomic mass. Production of X-rays Coolidge X-ray tube : Coolidge X-ray tube used … Read more
COMMUNICATION SYSTEM The setup used for exchanging information between a sender and receiver is called communication system. Information is specified as a measurable quantity in the technical description and the analytical treatment of the communication system. A message can be a sequence of distinct symbols or letters single time varying quantity i.e. speech,music,etc. many function … Read more
Scalars Quantities: Scalars are the physical quantities that have magnitude only.Temperature, speed, mass, and volume are examples of scalars. Vectors Quantities: Vectors are the physical quantities that have magnitude and direction.Position, displacement, velocity, acceleration and force are examples of vector quantities. Representation of a vector: A vector can be represented by a straight line with … Read more
Growth and decay of current in LR circuit Growth of current 1 and 2 are connected Current through circuit at any time t At t =0, I = 0 At t = ∞ , I = Io = (Vo/R) At any time t, where, τ = (L/R) = Inductive time constant Io = maximum value … Read more
Alternating current:An electric current whose magnitude varies continuously with time and changes its direction periodically, is called an alternating current. Alternating voltage:The voltage whose magnitude varies continuously with time and changes its direction periodically, is called an alternating voltage. Impedance: It is the measure of the opposition that a circuit offers to a current when … Read more
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