Network Theory Mcqs

Q:

Currents I?, I? and I? meet at a junction in a circuit. All currents are marked as entering the node. If I? = -6sin(?t) mA and I? = 8 cos(?t) mA, the I? is ________

A) 10 cos(?t + 36.87) mA B) 14 cos(?t + 36.87) mA
C) -14 sin(?t + 36.87) mA D) -10 cos(?t + 36.87) mA
 
Answer & Explanation Answer: D) -10 cos(?t + 36.87) mA

Explanation: Applying KCL, we get, I? + I? + I? = 0
? -6 sin(?t) + 8 cos(?t) + I? = 0
? I? = 6 sin (?t) – 8 cos (?t)
= 10[sin (?t).sin (36.86) – cos (?t) cos (36.86)]
=-10[cos (?t) cos (36.86) – sin (?t) sin (36.86)]
= -10 cos (?t + 36.86)
[As, cos (A+B) = cosA.cosB – sinA.sinB].

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80
Q:

The resistance of a thermistor decreases with increases in __________

A) temperature B) circuit
C) light control D) sensors
 
Answer & Explanation Answer: B) circuit

Explanation: The resistance of a thermistor decreases with increases in temperature. Hence, it is used to monitor hot spot temperature of electric machines.

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95
Q:

If A = 3 + j1, then A? is equal to __________

A) 3.16 ?18.4° B) 100 ?73.72°
C) 100 ?18.4° D) 3.16 ?73.22°
 
Answer & Explanation Answer: B) 100 ?73.72°

Explanation: Given A = 3 + j1
So, 3 + j1 = 10?18.43°
Or, 3 + j1 = (10)4 ?4 X 18.43°
= 100?73.72°.

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70
Q:

For making a capacitor, the dielectric should have __________

A) High relative permittivity B) Low relative permittivity
C) Relative permittivity = 1 D) Relative permittivity neither too high nor too low
 
Answer & Explanation Answer: A) High relative permittivity

Explanation: Relative permittivity is for ideal dielectric which is air. Achieving such a precise dielectric is very difficult.
Low relative permittivity will lead to low value of capacitance.
High relative permittivity will lead to a higher value of capacitance.

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114
Q:

A two branch circuit has a coil of resistance R1, inductance L1 in one branch and capacitance C? in the second branch. If R is increased, the dynamic resistance is going to ___________

A) Increase B) Decrease
C) Remains constant D) May increase or decrease
 
Answer & Explanation Answer: B) Decrease

Explanation: Not available for this question

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156
Q:

A capacitor, used for power factor correction in a single phase circuit decreases which of the following?

A) Power factor B) Line current
C) Both Line current and Power factor D) Neither Line current nor Power factor
 
Answer & Explanation Answer: B) Line current

Explanation: We know that a capacitor is used to increase the Power factor. However, with decrease in line current the power factor is increased. Hence line current decreases.

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191
Q:

Consider the impedance function, Z(s)=(2s²+8s+6)/(s²+8s+12). Find the value of R? after converting into second Cauer form.

A) 1/5 B) 14/5
C) 5/14 D) 5
 
Answer & Explanation Answer: B) 14/5

Explanation: The value of R? is 14/5? as the fifth quotient obtained is 5/14.
R? = 5/14?.

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64
Q:

Consider the impedance function, Z(s)=(2s²+8s+6)/(s²+8s+12). Find the value of L? after converting into second Cauer form.

A) 5/50 B) 10
C) 5/49 D) 49/5
 
Answer & Explanation Answer: C) 5/49

Explanation: We obtain the fourth quotient i.e., 1/sL? as 49/5s. So the value of L? is 5/49 H.
L? = 5/49H.

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