31. For the circuit of the given figure with an ideal operational amplifier, maximum phase shift of the output V_out with reference to the input V_in is
    

1. 1. 0°

   
   
   

   2. – 90°

   
   
   

   3. + 90°

   
   
   

   4. + 180°

   
   
   

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1. View Hint View Answer Discuss in Forum

   From the circuit,
   

   V+ =	Vin
   	1 + jωRC

   
   and V_– =V₊ (Ideal OPAMP) Now
   

   Now	Vin - V–	=	V– – V0
   	R1		R1

   
   ⇒ V₀ = 2V_– – V_in = 2V₊ – V_in
   

   =		2	- 1		Vin =	1 - jωRC	V0
   		1 + jωRC				1 + jωRC

   
   ∴ ∠ (V₀ / V_i) = - 2 tan^-1 ωRC
   For – 90 ≤ θ ≤ 90°
   Phase-shift ∠ (V₀ / V_i) = ± 180°
   

   Correct Option: D

   From the circuit,
   

   V+ =	Vin
   	1 + jωRC

   
   and V_– =V₊ (Ideal OPAMP) Now
   

   Now	Vin - V–	=	V– – V0
   	R1		R1

   
   ⇒ V₀ = 2V_– – V_in = 2V₊ – V_in
   

   =		2	- 1		Vin =	1 - jωRC	V0
   		1 + jωRC				1 + jωRC

   
   ∴ ∠ (V₀ / V_i) = - 2 tan^-1 ωRC
   For – 90 ≤ θ ≤ 90°
   Phase-shift ∠ (V₀ / V_i) = ± 180°
   

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32. The transfer function of a second order LP filter shown in the given figure is
    

1. 1. 	1
      	R2C2s2 + 3RCs + 1

   
   
   

   2. 	RCs
      	R2C2s2 + 3RCs + 1

   
   
   

   3. 	R2C2s2 + 1
      	R2C2s2 + 3RCs + 1

   
   
   

   4. 	R2C2s2
      	R2C2s2 + 3RCs + 1

      
      

   
   
   

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1. View Hint View Answer Discuss in Forum

   
   Using ∆ – Y conversion,
   

   Z1 =	R2Cs
   	2RCs + 1

   
   

   Z2 =	R
   	2RCs + 1

   
   

   Z3 =	R
   	2RCs + 1

   
   From the figure, using KCL, we have
   

   V0	=	1
   Vin		R2C2s2 + 3RCs + 1

   
   

   Correct Option: A

   
   Using ∆ – Y conversion,
   

   Z1 =	R2Cs
   	2RCs + 1

   
   

   Z2 =	R
   	2RCs + 1

   
   

   Z3 =	R
   	2RCs + 1

   
   From the figure, using KCL, we have
   

   V0	=	1
   Vin		R2C2s2 + 3RCs + 1

   
   

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33. The low frequency gain of the low pass filter shown in the given figure is
    
    

1. 1. 10 dB

   
   
   

   2. 20 dB

   
   
   

   3. 30 dB

   
   
   

   4. 40 dB

   
   
   

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1. View Hint View Answer Discuss in Forum

   	V2		=	R	.	1
   	V1			R1		RCs + 1

   
   

   = 100	1	≈ 100
   	10-3 j + 1

   
   

   ∴ 20 log		V2		= 40 dB
   		V1

   Correct Option: D

   	V2		=	R	.	1
   	V1			R1		RCs + 1

   
   

   = 100	1	≈ 100
   	10-3 j + 1

   
   

   ∴ 20 log		V2		= 40 dB
   		V1

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34. Feedback factor for the circuit shown in the given figure is
    
    

1. 1. 9/100

   
   
   

   2. 9/10

   
   
   

   3. 1/9

   
   
   

   4. 1/100

   
   
   

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1. View Hint View Answer Discuss in Forum

   Feed back factor =	10	=	1
   	1000		100

   Correct Option: D

   Feed back factor =	10	=	1
   	1000		100

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35. For the circuit shown in figure, true relation is
    
    

1. 1. v_o1 = v_o2

   
   
   

   2. v_o1 = – v_o2

   
   
   

   3. v_o = 2v_o2

   
   
   

   4. 2v_o1 = v_o2

   
   
   

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1. View Hint View Answer Discuss in Forum

   At second stage input to both op-amp circuit is same. Upper op-amp circuit is buffer having gain, AV = 1. Lower op-amp circuit is inverting amplifier having gain
   

   Aυ = -	R	= - 1
   	R

   
   ∴ υ₀₁ = – υ₀₂

   Correct Option: B

   At second stage input to both op-amp circuit is same. Upper op-amp circuit is buffer having gain, AV = 1. Lower op-amp circuit is inverting amplifier having gain
   

   Aυ = -	R	= - 1
   	R

   
   ∴ υ₀₁ = – υ₀₂

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