Quiz: Electrical Engineering 13 Aug 2020

Quiz: Electrical Engineering
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/3 mark
Time: 10 Minute

Q1. Dielectric strength is expressed in
(d)None of the above

Q2. The dielectric power loss(P) is given by
(a)P=2πf^2 CV tanδ
(b)P=2πfCV^2 tanδ
(c)P=4πfCV tanδ
(d)P=2πf^2 C^2 V^2 tanδ

Q3. Determine the quality factor of a series RLC circuit, when the value of capacitance is 0.02 mF, the value of inductance is 8 mH and the value of resistance is 40 ohms.

Q4. Which of the following is CORRECT about series RLC circuit?
(a)Its bandwidth decreases with decrease in inductance.
(b)Its bandwidth decreases with decrease in resistance.
(c)Its bandwidth decreases with increase in resistance.
(d)Its bandwidth is independent of both inductance and resistance.

Q5. The critical temperature at which high ferromagnetic materials lose their magnetism is called
(a)Curie Point
(c)Transition temperature
(d)Standard temperature

Q6. No-load speed of which of the following motor is highest?
(a)Differentially compound motor
(b)Cumulative compound motor
(c)Series Motor
(d)Shunt Motor

Q7. The compensating winding in the DC machine is
(a)Located in the armature slot for the compensation of armature reaction
(b)Located on commutating poles for Improving the commutation
(c)Located on pole shoes for avoiding the flashover at the commutator surface.
(d)Located on the pole shoe to avoid the sparking at the brushes

Q8. Which of the following statement is true about the windings of a 2-windings transformer?
(a) Windings are conductively linked
(b) Windings are inductively linked
(c) Windings are not linked at all
(d) Windings are electrically linked

Q9. An ideal voltmeter has ___________ equivalent resistance and ideal ammeter has ___________ equivalent resistance.
(a) Unity, Unity
(b) Zero, infinite
(c) Infinite, Zero
(d) Zero, Zero

Q10. According to the IS code, the colour of earth wire is usually:


S1. Ans.(a)
Sol. The dielectric strength of a material is a measure of the electrical strength of an insulator. It is defined as the maximum voltage required to produce a dielectric breakdown through the material and is expressed in terms of Volts per unit thickness. The higher the dielectric strength of a material the better an electrical insulator it makes.
Dielectric strength is expressed as: kV/mm

S2. Ans.(b)
Sol. The value of dielectric losses P in an insulating material having a capacitance C
is described as:
P = V Ia = V Ir tan 𝛿
Inserting the intensity of the capacitive current through an insulation portion
with a capacitance of C,
Ir = V𝜔C
Since 𝜔=2𝜋f, the angular frequency, the dielectric losses P can be expressed
As P = V^2 ωC tan δ = 2πfCV^2 tanδ

S3. Ans.(a)
Sol. The Quality factor of the series RLC circuit is given as:
Q=1/R √(L/C)=1/40 √((8×10^(-3))/(0.02×10^(-3) ))=0.5

S4. Ans.(b)
Sol. The bandwidth of the series RLC circuit is given as
B.W = R/L
Hence BW α R, so bandwidth decreases with decrease in resistance and vice-versa.

S5. Ans.(a)
Sol. Below the Curie temperature, the atoms are aligned and parallel, causing spontaneous magnetism; the material is ferromagnetic.
Above the Curie temperature the material is paramagnetic, as the atoms lose their ordered magnetic moments when the material undergoes a phase transition.

S6. Ans.(c)
Sol. At no load, armature current tends to zero, flux φ tends to zero, where speed is inversely proportional to the flux, speed will tend to infinity. Thus, no load speed of DC series motor is highest.

S7. Ans.(c)
Sol. Compensating winding is also known as pole face winding. This winding is embedded in the slots in pole faces. It is connected in series with the armature winding so that their mmfs are proportional to the same current. To compensate the effect of armature reaction, the direction of current in compensating winding must be opposite to that in the armature winding.
The trouble of flashover due to the distortion of flux density wave under the pole shoe is overcome by the use of compensating winding.

S8. Ans.(b)
Sol. in transformer, there is no electrical connection. Winding are linked inductively and transformer works on the principle of EMI.

S9. Ans.(c)
Sol. An ideal voltmeter has Infinite equivalent resistance and ideal ammeter has zero equivalent resistance.

S10. Ans.(b)
Sol. earth wire—green
Neutral wire………black
Phase wire…………red

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