56. In a balanced Wheatstone bridge, if the positions of detector and source are interchanged, the bridge will still remain balanced. This inference can be drawn from—

1. 1. reciprocity theorem

   
   
   

   2. duality principle

   
   
   

   3. compensation theorem

   
   
   

   4. equivalance theorem
      

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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57. The value of the resistance R in the circuit shown in the given figure is varied in such a manner that the power dissipated in 5 Ω resistor is maximum. Under this condition, the value of R will be—
    
    
    

1. 1. 20 Ω

   
   
   

   2. 40	Ω
      3

   
   
   

   3. Ω

   
   
   

   4. 30 Ω

   
   
   

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1. View Hint View Answer Discuss in Forum

   Power draw through the 5 Ω (i.e. load resistance) will be maximum if and only if R_th = R_L calculation for R_th for the given circuit.
   
   

   Rth =	8 R
   	8 + R

   
   

   	8 R	= 5
   	8 + R

   
   8R = 5R + 40
   3R = 40
   

   R =	40	Ω
   	3

   Correct Option: B

   Power draw through the 5 Ω (i.e. load resistance) will be maximum if and only if R_th = R_L calculation for R_th for the given circuit.
   
   

   Rth =	8 R
   	8 + R

   
   

   	8 R	= 5
   	8 + R

   
   8R = 5R + 40
   3R = 40
   

   R =	40	Ω
   	3

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58. Calculate the Thevenin resistance for the circuit shown below between A and B—
    
    
    

1. 1. 10 Ω

   
   
   

   2. 12 Ω

   
   
   

   3. 20 Ω

   
   
   

   4. 18 Ω

   
   
   

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1. View Hint View Answer Discuss in Forum

   Calculation of Rth:
   
   R_th = 10 + (2 + 2) || 4
   

   = 10 +	4 × 4
   	4 + 4

   
   = 10 + 2 = 12 Ω

   Correct Option: B

   Calculation of Rth:
   
   R_th = 10 + (2 + 2) || 4
   

   = 10 +	4 × 4
   	4 + 4

   
   = 10 + 2 = 12 Ω

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59. The rms voltage measured across on admittance (G + jB) is V. The reactive power for the element is—

1. 1. V² B

   
   
   

   2. – V² B

   
   
   

   3. V² G² + B²

   
   
   

   4. V² (G + jB)

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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60. If L {f (t)} =
    	s2 + 2

    , then the value of lim t→∞ f (t)—

1. 1. cannot be determined

   
   
   

   2. Zero

   
   
   

   3. 1

   
   
   

   4. ∞

   
   
   

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1. View Hint View Answer Discuss in Forum

   Given, L {f (t)} =
   	s2 + 2

   
   or f (t) = sin t.
   as t → ∞, f (t) = sin t goes through 1 to 0
   and – 1 to 0 to infinite times so the value of Lim t→∞ f(t) cannot be determined.

   Correct Option: A

   Given, L {f (t)} =
   	s2 + 2

   
   or f (t) = sin t.
   as t → ∞, f (t) = sin t goes through 1 to 0
   and – 1 to 0 to infinite times so the value of Lim t→∞ f(t) cannot be determined.

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