Objective Questions on Circuit Theory | Page – 3

1. For the circuit given in the figure, the Thevenin voltage and resistance as seen at AB are represented by

2. Form factor is defined as ratio of

$Form\; Factor = \frac{RMS\; Value}{Average\; Value}$

3. Peak factor is defined as ratio of

$Peak\; Factor = \frac{Maximum\; Value}{RMS\; Value}$

4. At resonance

Resonance is occurs at when inductive, capacitive reactance both are same i.e. , circuit is having only resistive components.

5. A series R-L-C circuit has R=50 Ω, L=100 μH and C = 1 μF. The lower half power frequency of the circuit is

 Ω1.L − 1 = − R Ω1.C
 2πf1X100X10 − 6 − 1 = − 50 ⇒ f1 = 3.055 KHz 2πf1.X1X10 − 6

6. The period of the function cosπ/4(t-1) is

Here 2π / T = π / 4 ⇒ T = 8 Second.

7. A T-section lowpass filter has series inductor 80 mH and shunt capacitance 0.022 μF. What is the cutoff frequency?

L = 80 mH, C = 0.022 μF , fc (cutoff frequency) = 1 /π√(LC) = 1 / π√(80 × 10 − 3) × (0.022 × 10 − 6) = 7.58 KHz.

8. In a constant-k high pass filter having cutoff frequency of 12 kHz. Find out phase constant at 24 kHz?

β ( phase constant ) = 2sin − 1(fc/f) = 2sin − 1(12 × 103/24 × 103) = 60°.

9. In Constant K high- pass filter having cutoff frequency of 12 KHz. Find out attenuation at 4 KHz?

α ( attenuation ) = 2cosh − 1(fc/f) = 2cosh − 1(12 × 103/4 × 103) = 3.525 Neper.

10. Find out the series arm capacitance &s; shunt arm inductor in a constant K-high pass filter, when impedance R0 = 600 Ω &s; cut off frequency = 4 Khz (Π - sec)

C = 1 / 4πR0fc = 1 / (4π600 × 4000) = 0.033 μF and L = R0/ 4πfc = 600 / (4π × 4000) = 11.937 mH.

11. An RLC circuit has a resonance frequency of 160 kHz and a Q-factor of 100. Its band width is

Bandwidth, Bω = f0/Q
Where f0 = Resonant frequency.
Q = Quality factor.
Bω = 160/100 = 1.6 kHz.

12. A circuit which has ω0 = 106 rad/sec (ω0 = resonant frequency) C = 10 pf and Q = 100, must have a resistance of ___________kΩ.

Q= Xc/R ⇒ R= 1/ (ω0CQ) = 1 / (106 × 10 × 10-12 × 100) = 100 × 103 Ω .

13. A certain ac circuit has resistance of 10 ohm and impendence of 20 ohm. The phase angle of voltage and current of the circuit is

cosφ = R/Z = 10/20.
φ = cos-1(1/2)= 60°.

14. The time constant of an RL circuit is 1 second and its inductor is 8 H, the resistance of the coil is _____ ohms.

Time constant of RL circuit = L/R
T = L/R
⇒ 1 = 8/R
⇒ R = 8 ohm.

15. The period of the function cos π/4(t-1) is

Here 2π/T=π/4 or,T=8 Second.

16. Clamping circuits are one which inserts

Clamping circuits / dc restorer are one which inserts dc components. These circuits are used in television amplifiers. A clamping circuit (also known as a clamper) will bind the upper or lower extreme of a waveform to a fixed DC voltage level. Clamp circuits are categorized by their operation; negative or positive, and biased or unbiased.

17. To a highly inductive circuit , a small capacitance is added in series . The angle between voltage and electric current will

The angle between voltage and electric current decreases when capacitance is added in series to a highly inductive circuit.

18. Value of electric current at resonance in a series RLC circuit is affected by the value of

In series RLC circuit value of electric current is always affected by inductor of the circuit.

19. Superposition theorem is not applicable to networks having

Superposition is only applicable to networks having linear elements.

20. A network is linear if

A linear network obeys both the principle of superposition and homogeneity.