Aditya Abeysinghe Presentations

A calomel electrode ( popularly called Saturated calomel electrode or SCE) is a based on the reaction between elemental mercury and mercury(I) chloride (calomel).  It is used as a reference electrode in many electrochemical experiments since its electric potential is known. It is also sometimes used in pH calculations and cyclic voltammetry. (Photo credit: dc181.4shared.com) The aqueous phase in contact with the mercury and the mercury(I) chloride (Hg 2 Cl 2 , "calomel") is a saturated solution of potassium chloride in water. In this electrode, the activity of the metal ion is fixed by the solubility of the metal salt. Thus, the half reaction that occurs inside this electrode can be denoted as follows: Hg 2 2+  + 2e   ↔    2Hg    (Note that in the above reaction the left-right arrow represents that this reaction is under equilibrium conditions or that both the forward and the reverse reactions ar...

What is Bernoulli's equation? Bernoulli's equation is a relationship between pressure and velocity at different parts of a moving incompressible fluid. The following two assumptions must be met for this Bernoulli equation to apply: the flow must be incompressible – even though pressure varies, the density must remain constant along a streamline friction by viscous forces has to be negligible. Bernoulli's principle- Bernoulli's principle states that for a incompressible, streamline and non viscous fluid, the work done by the pressure difference per unit volume plus the kinetic energy per unit volume plus the potential energy per unit volume is a constant. Work done = Force  ∗ distance Force = Pressure  ∗ Area. Thus, Work = Presssure  ∗ Area  ∗ distance. Thus, Work = Pressure  ∗ Volume. Therefore, the work done per unit volume = Pressure. Kinetic energy = 1/2  ∗ mass  ∗ velocity 2 Therefore, kinetic energy per...

In this note I will present details only about the npn transistor. For those who are interested only on the pnp transistor, you can switch the action of the npn transistor and the behavior of current to adjust with the characteristics of the pnp transistor. (Photo credit: mahasona10000.blogspot.com ) As in the case of a p-n junction,the two n parts of the npn transistor contain an excess of free electrons. In contrast, the p part contains excess holes. As in the case of the p-n junction, in the npn transistor depletion regions develop and junction barriers occur. (Photo credit: daenotes.com) For the correct functioning of the transistor, the first p-n junction is forward biased and the second p-n junction is reverse biased. This results for the first p-n junction to be of low resistance and the second p-n junction to be of high resistance. (Photo credit: www.nzart.org.nz ) The letters of t...

What is a gold leaf electroscope? Gold leaf electroscope is an instrument for detecting and measuring static electricity or voltage. The following diagram shows a modern gold leaf electroscope: Why is gold used to make such an electroscope? Gold is popularly used to make such electroscopes since gold is even sensitive to very minute charges (This is achieved by the malleability of gold - hammering into sheet form and making the mass thin). When we introduce a charged object to the disk of the electroscope ( explained below) we practically do not know the magnitude of the charge. Thus a simple conductor may not be the best option to show a reasonable deflection or response even to minute charges. Thus gold is assumed to be sensitive to charges of any magnitude which makes it more suitable as the indicator.  Besides gold is also a non corrosive metal. We practically do not use anhydrous materials inside the glass case. The penetration...

What is Lenz's law? An electric current induced by a changing magnetic field will flow such that it will create its own magnetic field that opposes the magnetic field that created it. Lenz's law is sometimes similar to the Faraday's law in that both laws discuss about induction. However, Lenz's law clearly demonstrates the direction of the induced current as opposed to the theoretical observation by the Faraday's law. To understand Lenz's law, consider the system below: (Photo credit: www.pinkmonkey.com) Before explaining this system using Lenz's law, let us remind about the direction of the field lines around the magnet. Now let us consider the above system in detail. Consider Fig 1(a): When the north pole is brought close to the magnet, the field lines will be as follows:  As Lenz's law states ' an electric current induced by a changing magnetic field will fl...

What is electromagnetic induction? When an alternative current is allowed to flow through a certain circuit and that circuit is kept near a neutral circuit, the former circuit induces charge distributions in the latter circuit resulting in an induced current in the latter circuit. This phenomenon is called the electromagnetic induction. Thus a potential difference arises across the circuit when exposed to a varying magnetic field. Faraday's law- Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil.  (Photo credit: gic-edu.com) Thus, fluctuating magnetic fields cause currents to flow in conductors placed within them. This is called induction because there is no physical connection between the conductor and the magnet. The current is said to be induced in the conductor by the magnetic field. In order to produce the maximum force needed for induction, usually the cond...