21. The period of the output waveform for the circuit of figure shown, when triggered by a negative pulse is
    
    

1. 1. 0.75 ms

   
   
   

   2. 0.825 ms

   
   
   

   3. 0.525 ms

   
   
   

   4. 1.5 ms

   
   
   

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1. View Hint View Answer Discuss in Forum

   T = (1.1) R_AC
   = 1.1(7.5 × 10³) (0.1 × 10^{– 6}) = 0.825 ms.

   Correct Option: B

   T = (1.1) R_AC
   = 1.1(7.5 × 10³) (0.1 × 10^{– 6}) = 0.825 ms.

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22. The circuit shown in the figure
    
    

1. 1. is an oscillating circuit and its output is a square wave

   
   
   

   2. is one whose output remains stable in ‘1’ state

   
   
   

   3. is one having output semains stable in ‘0’ state

   
   
   

   4. having a single pulse of 3 times propagation delay.

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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23. For the oscillator circuit shown in the given figure, expression for the time period of oscillation can be given by (where t = RC)
    
    

1. 1. τ ln 3

   
   
   

   2. 2 τ ln 3

   
   
   

   3. τ ln 2

   
   
   

   4. 2 τ ln 2

   
   
   

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1. View Hint View Answer Discuss in Forum

   T = 2RC ln	1 + β
   	1 - β

   
   

   Here , β =	1	=	R
   	2		R + R

   
   ∴ T = 2 RC ln 3 = 2 τ ln 3

   Correct Option: B

   T = 2RC ln	1 + β
   	1 - β

   
   

   Here , β =	1	=	R
   	2		R + R

   
   ∴ T = 2 RC ln 3 = 2 τ ln 3

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24. A voltage source V_AB = 4 sinωt is applied to the terminals A and B of the circuit shown in the given figure. The diodes are assumed to be ideal. The impedance by the circuit across the terminals A and B is _________ kΩ .
    
    

1. 1. 10

   
   
   

   2. 20

   
   
   

   3. 45

   
   
   

   4. 66

   
   
   

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1. View Hint View Answer Discuss in Forum

   Diode D₁ conducts through 10 kΩ on the extreme right and diode D₂ is blocked. Diode D₂ conducts through 10 kΩ in the middle branch and diode D₁ is blocked. Thus source always sees a resistance of 10 kΩ.

   Correct Option: A

   Diode D₁ conducts through 10 kΩ on the extreme right and diode D₂ is blocked. Diode D₂ conducts through 10 kΩ in the middle branch and diode D₁ is blocked. Thus source always sees a resistance of 10 kΩ.

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25. If α = 0.98, I_CO = 6 µA and I_β = 100 A for a transistor, then value of I_C will be _______ mA

1. 1. 15.2

   
   
   

   2. 5.2

   
   
   

   3. 2.2

   
   
   

   4. 8.4

   
   
   

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1. View Hint View Answer Discuss in Forum

   IC =	ICO	+	α	IB =	6	+	0.98	× 100 = 5.2 mA
   	1 - α		1 - α		1 - 0.98		1 - 0.98

   
   

   Correct Option: B

   IC =	ICO	+	α	IB =	6	+	0.98	× 100 = 5.2 mA
   	1 - α		1 - α		1 - 0.98		1 - 0.98

   
   

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