Tag: electro-magnetism

Transformers are used only in A.C. Circuits because D.C. current could not produce changing flux which in turn not able to produce induced emf in the secondary coil of the transformer but A.C. Current produces changing flux.

The Voltage Transformer can be thought of as an electrical component rather than an electronic component. A transformer basically is very simple static (or stationary) electro-magnetic passive electrical device that works on the principle of Faraday’s law of induction by converting electrical energy from one value to another.

The transformer does this by linking together two or more electrical circuits using a common oscillating magnetic circuit which is produced by the transformer itself. A transformer operates on the principals of “electromagnetic induction”, in the form of  $Mutual$ $ Induction$.

Mutual induction is the process by which a coil of wire magnetically induces a voltage into another coil located in close proximity to it. Then we can say that transformers work in the “magnetic domain”, and transformers get their name from the fact that they “transform” one voltage or current level into another.

Answer is A.

A transformer 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.
If we change the number of turns in the coils we change the induced emf. This allows us to change (transform) the voltage from the primary to the secondary coil.
The Turns Rule is:
Ns/Np=Vs/Vp
Where,
Ns = number of turns on the secondary coil
Np = number of turns on the primary coil
Vs = voltage across the secondary coil
Vp = voltage across the primary coil
So if number of turns on the secondary coil is more than on the primary coil, the output voltage will be higher than the input voltage. This is called a step up transformer.
Hence, The secondary voltage as per the given question can be obtained as follows:
Let input voltage be 6V and the output voltage be x. Let 5000 be the number of turns of secondary coil and 500 be the number of turns of primary coil.
Ns/Np=Vs/Vp; 
That is, 5000/500=x/6 
$x=\frac { 5000\times 6 }{ 500 } =60\quad V$.
Therefore, the secondary voltage is 60 V.

Answer is D.

The efficiency of a transformer can be calculated using Equation,
$Efficiency\quad =\quad \frac { Output\quad power\quad of\quad the\quad transformer }{ Input\quad power\quad of\quad the\quad transformer } \quad =\quad \frac { { P } _{ s } }{ { P } _{ p } } \times 100$
In this case, the output power is calculated as follows.
The output voltage is 11 V and current is 90 A
$Power\quad =\quad VI\quad =\quad 11\times 90=990W$.
The input power is calculated as follows.
The input voltage is 220 V and current is 5 A
$Power\quad =\quad VI\quad =\quad 220\times 5=1100W$.
So, $\eta =\quad \frac { 990 }{ 1100 } \times 100\quad =\quad 90%$.
The efficiency of the transformer is 90%.

A

An electric motor is an electrical machine that corrects electrical energy into mechanical energy. Working of electric motor mainly depends upon the interaction of magnetic field with current.

Answer is A.
Mutual inductance is where the magnetic field generated by a coil of wire induces voltage in an adjacent coil of wire. A transformer is a device constructed of two or more coils in close proximity to each other, with the  purpose of creating a condition of mutual inductance between the coils.

Answer is A.

The rate at which alternating current reverses direction is called its frequency, expressed in hertz. Thus, standard household current in India is 50 Hz. AC electricity alternates back-and-forth in direction 50 times per second, according to the electrical system in the country. The charge at the ends of the wire alternates between negative (-) and positive (+). If the charge is negative (-), that pushes the negatively charged electrons away from that terminal. If the charge is positive (+), the electrons are attracted in that direction. Thus the electricity in the wire moves in one direction for a short while and then reverses its direction when the generator armature is in a different position. The direction changes twice in each cycle so that change of direction takes place after every 1/100 second.

AC voltage, It also helps in regulation the level of AC voltage

Answer is C.

Transformers are capable of either increasing or decreasing the voltage and current levels of their supply, without modifying its frequency, or the amount of Electrical Power being transferred from one winding to another via the magnetic circuit. So the current is sent through step up transformers to increase the voltage and to push the power over long distances.

Answer is C.

Transformers are capable of either increasing or decreasing the voltage and current levels of their supply, without modifying its frequency, or the amount of Electrical Power being transferred from one winding to another via the magnetic circuit. So the current is sent through step up transformers to increase the voltage and to push the power over long distances.
Hence, transformer is employed to obtain a suitable A.C. voltage.