Electromagnetic Shielding

What is electromagnetic shielding?

Electromagnetic induction is the process of reducing the electromagnetic field of space.

We know that electromagnetic waves are a combination of any two electric and magnetic waves held perpendicularly. Similarly, electromagnetic radiation is a combination of electric and magnetic fields.

(Photo credit: www2.astro.psu.edu)

Let's study these two systems separately.

Electric fields produces forces on the charge carriers within the conductor. When an electric field is applied to a certain conductor, it produces a current that causes the charges to move inside the conductor.

(Photo credit: www.learnemc.com )

Magnetic fields produces eddy currents. These eddy currents behave so as to cancel the applied magnetic field.

(Photo credit: www.mdpi.com)

All these result in the reflectance of the electromagnetic radiation from the surface of the conductor.

Because there are no free magnetic charges, it is not possible to terminate lines of magnetic flux on a shield. However, it is possible to redirect magnetic flux lines to prevent unwanted coupling. This can be done by inducing charges inside an electrically conductive shield.

(Photo credit: www.birmingham.ac.uk)

Magnetic fields are usually shielded with poor magnetic shields of conducting materials at low frequencies. This prevents the penetration of the losses in eddy currents as eddy currents are driven by time varying fields. Also, most conductors exhibit a ferromagnetic response to low-frequency magnetic fields.

That is, since eddy currents are time varying fields, losses in the conducting plate will result for the eddy currents to dissipate and this allows the magnetic flux to penetrate the plate.

(Photo credit: www.vias.org)

At these low frequencies permeable magnetic materials are used to divert magnetic fields. Furthermore, these shields should be spherical or should cover the whole object as shielding only a portion would result in the penetration of magnetic fields to the unshielded object.

Action of a transistor

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 these elements

Gold leaf electroscope

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 of

The Silver Mirror Test

What is the Silver Mirror Test? Silver Mirror Test is a test that is used to differentiate between aldose and ketose sugars using the Tollen's reagent. Tollen's reagent is an alkaline solution of ammoniacal silver nitrate and is used to test for aldehydes. *Ketones do not react with the Tollen's reagent. Silver ions in the presence of hydroxide ions form a brown precipitate of silver (I) oxide, Ag 2 O (s) . Ag 2 O This precipitate dissolves in aqueous ammonia, forming the diamminesilver(I) ion, [Ag(NH 3 ) 2 ] + . The reactions that take place in this experiment are as follows: 2Ag + (aq) + 2OH - (aq) → Ag 2 O (s) + H 2 O (l) Ag 2 O (s) + 4NH 3 (aq) + H 2 O (l) → 2[Ag(NH 3 ) 2 ] + (aq) + 2OH - (aq) What happens if Silver Nitrate is used without ammonia or why is ammonia used in this experiment? When ammonia is added to the silver nitrate solution, silver ions are less prone to reduction. Thus, silver is produce

Electromagnetic Induction

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

Flame test- By Aditya Abeysinghe

Introduction: Flame test is an experiment used to identify/distinguish metals using colors exposed to a flame. Since metallic halides easily evaporate, the test is usually done using the halide components of metals. Out of the halides, chlorides are frequently used because chlorides give a fast change of color when exposed to the flame as opposed to other halides. Materials needed: · A rod of platinum, nichrome, asbestos or graphite · Concentrated HCl solution · Bunsen burner · Metallic salt (a chloride of a metal) · A cobalt glass (if necessary) Method: Insert the rod of platinum, nichrome, asbestos or graphite into a concentrated solution of HCl. Hold the rod to a Bunsen flame. (to the colorless region) Continue this experiment until the top region of the flame turns colorless. Form a pulp by mixing the metallic salt with the concentrated HCl solution and apply

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