SESSION:25

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1)       Differentiate between ideal and non-ideal voltage sources?

The Ideal Voltage Source An ideal voltage source which has a terminal voltage which is independent of the variations in load. In other words, for an ideal voltage source, the supply current alters with changes in load but the terminal voltage, VL always remains constant.Non-Ideal or Practical Voltage Source For a practical source, the terminal voltage falls off with an increase in load current.

2)       What does the term “Voltage Regulation” means?

Voltage regulation (VR) is an important measure of the quality of a source. It is used to measure the variation in terminal voltage between no load (I_L =0, open circuit) and full load (I_L = I_FL) 

3)       What is DC Current source? Differentiate between ideal and non ideal current sources?

A current source, unlike the DC voltage source, is not a physical reality. However, it is useful in deriving equivalent circuit models of semiconductor devices such as a transistor. It can also be subdivided into ideal and non-ideal categories. The Ideal Current Source by definition, an ideal current source that produces a current which is independent of the variations in load. In other words the current supplied by an ideal current source does not change with the load voltage. Non-Ideal or Practical Current Source The current delivered by a practical current source falls off with an increase in load or load voltage.

4)       Define Super node?

A supernode exists when an ideal voltage source appears between any two nodes of an electric circuit. The usual way to solve this is to write KCL equations for both nodes and simply add them together into one equation ignoring the voltage source in question. However, this would mean one less equation than the number of variables (node voltages) present in the circuit. A constraint equation can be easily specified given by the magnitude of the ideal voltage source present between the nodes and the respective node voltages. The following example will help clarify this scenario.

5)       What does the term Supermesh means?

A supermesh exists when an ideal current source appears between two meshes of an electric circuit. In such a situation, like supernode, mesh equations are written for the meshes involved and added giving a single equation. Again, there would be one less equation than the number of variables (mesh currents) and hence a constraint equation is needed. This would be based on the magnitude of the ideal current source present between the two meshes and their mesh currents.

6)       What do you mean by Phasors?

Addition of two out-of-phase sinusoidal signals is rather complicated in the time domain. An example could be the sum of voltages across a series connection of a resistor and an inductor.
Phasors simplify this analysis by considering only the amplitude and phase components of the sine wave. Moreover, they can be solved using complex algebra or treated vectorially using a vector diagram.

7)       Differentiate between Real and Apparent Power?

It is important to highlight that in AC circuits, the product of voltage and current yields the apparent power which is measured in volt-amperes or VA
KW which is also written ad Kilo-Watt is the real power that is actually converted to the useful work.

KVAR is also termed as Kilo-Volt Reactive this power is used for magnetic field excitation and flows back and forth between source and load.

8)       What does Bode Plots shows?

Bode plots are a graphical way to display the behaviour of a circuit over a wide range of frequencies. By plotting the amplitude and phase versus the logarithm of frequency, each unit of change on the ω axis is equal to a factor of 10 also called a decade of frequency. Also, there may be a wide distribution in the amplitude response over a specified range of frequencies. The usual way is to plot the amplitude in dB and phase in degrees or radians versus the logarithm of frequency.

9)       Differentiate between Low Pass, High pass and Band Pass filter?

Filters form a vital part in electrical networks especially where a particular frequency range is of prime concern. For instance, a radio station is broadcasting a transmission at a frequency of 100 MHz. This means that it is required to design a receiving filter which allows only 100 MHz frequency to pass through whilst other frequencies are filtered out. An ideal filter will attenuate all signals with frequencies less than and greater than 100 MHz thus providing the best channel sound quality without any distortion. 

Low Pass Filter 

A low pass Filter allows low frequencies to pass through the circuit whereas high frequencies are severely attenuated or blocked. 

High Pass Filter 

A high pass filter, as the name suggests, allows high frequencies to pass through the circuit whilst low frequencies are attenuated or blocked. The cut-off point or bandwidth concept is the same as in the low pass filter. 

Band Pass Filter 

A band pass filter permits a certain band of frequencies to pass through the network which is adjusted by the designer. It is simply an amalgamation of a low pass and a high pass filter. 

10)    Differentiate between Magnetic field and Magnetic Flux?

Magnetic field is B = µ H where B is in Tesla and H = 1.26 x 10^-6 times ampere turns/metre MMF in a solenoid of N turns and current I mmf = (4 m / 10) N I Gilberts.
Whereas Magnetic flux ø= B A where ø is in Weber, B is in Teals and A is in square meters. 

Magnetic flux in a uniform closed magnetic circuit, length L meters and cross section A square meters is
=1.26NItAx10^-6/LWeber.

11)    What is Force on a conductor in a magnetic field?

F = B I L Newtons where B in tesla, I in amps and L in meters.

12)    Differentiate between Induced emf and Self inductance?

Induced emf , E = - N dø/dt where E is in volts, N is number of turns and dø/dt is in Wb/sec This equation is the foundation on which Electrical Engineering is based. 

Whereas Self Inductance E = - L dI/dt where E is in volts, L is inductance in henneries and dI/dt is in amps/sec Self inductance of a coil wound on a ring of permeability is L = 1.26 N2 μ A / S x 10-6 Henneries where N is number of turns, A is cross sectional area in m2 and S meters is the length of the magnetic circuit. Experimental results for a coil of length S meters, diameter d meters and radial thickness t meters with at core indicate L = 3 d2 N2 / (1.2 d + 3.5 S + 4 t) micro Henneries. (t = 0 for a single layer coil). 

13)    How to calculate Energy stored in an inductance?

Energy stored =1/2 L I² Joules where L is in henries and I is in amps.

14)    How to calculate Energy stored in a capacitance?

Energy stored =1/2 C V² Joules where C is in farads and V in volts.

15)    What are the different type of transformer earthing ? What is the function of transformer earthing?

The two types of earthing are familiar as equipment earthing and system earthing. In equipment earthing body of the equipment should be earthed to safeguard the human beings.

System earthing : In this neutral of the supply source should be grounded. With this in case of unbalanced loading neutral will not be shifted so that unbalanced voltages will not arise. We can protect the equipment also. With size of the equipment and selection of relying system earthing will be further classified into directly earthed, Impedance earthing, resistive.