General Electrical Engineering Questions – 2

(1) The common voltage across parallel branches with different voltage sources can be determined by the relation V = (V₁ / R₁ + V₂ / R₂ + V₃ / R₃) / ( 1 / R₁ + 1 / R₂ +1 / R₃ …..) The statement is associated with which theorem ?

· Superposition theorem.

· Thevenin’s theorem.

· Norton’s theorem.

· Millman’s theorem.

The Millman’s theorem states that the voltage at the ends of the circuit is given by

Here,

V_K is the voltage generators and I_M the current generators.

R_I is the resistances on the branches with no generator.

R_K is the resistances on the branches with voltage generators.

R_M is the resistances on the branches with current generators.

Hence, the given voltage relation is clearly matched with the above formula. Thus, the statement is associated with the Millman’s theorem.

(2) The number of independent equations to solve a network is equal to

· number of chords.

· number of branches.

· sum of number of branches and chords.

· sum of number of branches , nodes and chords.

The chords are nothing but the group of three or more nodes connected together. Each node has loop equations. That equation is independent to each other. Hence, the number of independent equations to solve a network is equal to its number of chords.

(3)Which of the following is not a vector quantity?

· Linear momentum.

· Angular momentum.

· Electric field.

· Electric potential.

We know that the electrical potential is E = – ΔVE. It is nothing but the amount of work needed to get a positive charge to that spot. It is a scalar quantity because work is not a vector quantity. However, scalars are allowed to be negative. The minus sign on the potential does not indicate the vector direction. A negative potential can be attracted by a positive potential and repulsed by another negative potential.

(4) What is the dielectric constant of mica ?

· 200.

· 100.

· 3-8.

· 1-2.

The following are dielectric constant of different materials. They are,

1. Vacuum – 1 2. Glass – 5 to 10 3. Mica – 3 to 8

4. Mylar – 3.1 5. Neoprene – 6.70 6. Plexiglas – 3.40

7. Polyethylene – 2.25 8. Polyvinyl chloride – 3.18 9. Teflon – 2.1

10. Germanium – 16 11. Strontium titanate – 310 12. Water – 80.4

13. Glycerin – 42.5 .

(1) Magnetic moment is a

· pole strength.

· universal constant.

· scalar quantity.

· vector quantity.

The magnetic moment can be considered to be a vector quantity with direction perpendicular to the current loop in the right hand rule direction. The amount of magnetic moment created by the current loop is μ = I × A. Where, I is current flowing through the loop and A is the area covered by the loop. So, the torque generated by the magnetic moment is T = μ × B. Where, B is the magnetic field. This torque tends to line up the magnetic moment with the magnetic field B, so this represents its lowest energy configuration. The potential energy associated with the magnetic moment is U (ø) = – μ × B. The negative sign represents that the magnetic moment is vector quantity.

(6) Temporary magnets are used in which of the following ?

· Loud speakers.

· Generators.

· Motors.

· All of these.

Permanent magnets lose their power after some days. So, if we use permanent magnet in those equipment, then it does not give efficient output throughout its entire life span. But, the above mentioned equipment have to work efficiently at all time. That is why the temporary magnets (or) the electromagnets are used in the above mentioned machines.

(7)Autotransformer makes effective saving on copper and copper losses, when its transformation ratio is equal to

· approx to one.

· less than one.

· greater than one.

· none of the above.

To quantify the saving the total quantity of copper used in an auto transformer is expressed as a fraction of that used in a two winding transformer as,

This means that an auto transformer requires the use of lesser quantity of copper given by the ratio of turns. Hence, if the transformation ratio is approximately equal to one, then the copper saving is good and the copper loss is less.

(8) The noise resulting from vibrations of lamination set by magnetic forces, is termed as

· magnetostriction.

· boo.

· hum.

· zoom.

The hum is generated by the magnetic field that happens due to the continuous reversing of the frequency of the supply. The magnetic field in the AC machine or transformers has coils which are still able to move slightly due to the vibration. The laminations of the armature are treated in a similar way but also vibrate at the line frequency and it is almost impossible to stop. We can only reduce it by good design.

(9)In circle diagram for induction motor, diameter of circle represents which of the following ?

· Slip.

· Rotor current.

· Running torque.

· Line voltage.

Basically in the circle diagram for an induction motor, the diameter of the circle represents the rotor current and by using that circle, the current per phase with rotor blocked and full voltage on stator and the line current in amperes for any chosen load can be found.

(10) Tarapur nuclear power plant has which type of reactor?

· Pressurized water reactors.

· Boiling water type.

· CANDU type reactors.

· None of these.

The Tarapur nuclear power plant has initially built with two boiling water reactor with the capacity of 210 MW on 1969. But, now this plant has built extra two pressurized heavy water reactor with the capacity of 540 MW on 2006.

THE ELECTRICAL INDIA

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