Tag: electro-magnetism

Transmission losses are given as $I^2R$. In AC, voltage transformation to higher(and also lower) values is easier at constant power. So, voltage is increased before transmission reducing current and hence reducing transmission losses.

Transformer is an electrical device that requires time varying current to link two or more electrical coils through electromagnetic induction and thus transfer energy between the magnetically coupled circuits. Therefore transformer are used only in AC circuits

Since, the starter motor draws a large current resulting in a large potential drop in the battery, which reduced the thermal voltage of the battery hence, the light of a car are dim when the starter is operated.

The iron core of a transformer is made of Laminated silicon steel with special insulated coating to limit Eddy current loss. Electrical steel, also called lamination steel is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area (small energy dissipation per cycle, or low core loss) and high permeability.
An eddy current is a swirling current set up in a conductor in response to a changing magnetic field. By Lenz's law, the current swirls in such a way as to create a magnetic field opposing the change. To do this in a conductor, electrons swirl in a plane perpendicular to the magnetic field. Because of the tendency of eddy currents to oppose, eddy currents cause energy to be lost. More accurately, eddy currents transform more useful forms of energy, such as kinetic energy, into heat, which is generally much less useful. 

In electric motor electrical energy is converted into mechanical energy hence, option D is correct.

Transformers are found everywhere alternating current is used. This includes both large power stations to the power cord for our laptop computer. A transformer is an electrical device that trades voltage for current in a circuit, while not affecting the total electrical power. This means it takes high-voltage electricity with a small current and changes it into low-voltage electricity with a large current, or vice versa. That is, step up or step down the voltage in a circuit.
A step-up transformer turns low-voltage electricity into high-voltage electricity while dropping the current. A step-down transformer changes high-voltage electricity into low-voltage electricity.
Therefore, to convert 12V a.c. to 200V a.c., a step up transformer is used.
This transformer works in the principle of Electromagnetic induction which states that rate of change of flux linkage with respect to time is directly proportional to the induced EMF in a conductor or coil.
Say we have one winding which is supplied by an alternating electrical source. The alternating current through the winding produces a continually changing flux or alternating flux that surrounds the winding. If any other winding is brought nearer to the previous one, obviously some portion of this flux will link with the second. As this flux is continually changing in its amplitude and direction, there must be a change in flux linkage in the second winding or coil. According to Faraday's law of electromagnetic induction, there must be an EMF induced in the second. If the circuit of the later winding is closed, there must be an current flowing through it. This is the simplest form of electrical power transformer and this is the most basic of working principle of transformer.

A step up transformer increases the voltage This transformer has more windings on the "secondary" side of the transformer, with fewer windings of thicker wire on the primary or input coil. 

A transformer takes in electricity at a higher voltage and lets it run through lots of coils wounded around an iron core. Because the current is alternating, the magnetism in the core is also alternating. Also around the core, there is an output wire with fewer coils. The magnetism changing back and forth creates a current in the wire. Having fewer coils means less voltage. So the voltage is "stepped-down."