21. An inductor is connected with A.C source, during 1st quarter cycle when both I and V are positive, this means energy is:

A.  Supplied to inductor                
B. Zero in inductor


   
C. Returned by inductor                
D. Dissipated in heat
 

22. The reactance of an inductor at 50 Hz is 10 . Its reactance at
100 Hz is:

A. 2.5                                  
B. 10 
       
C. 5                                     
D. 20 
 

23. A resistor R and capacitor C are connected in series across an A.C source of rms voltage 5V. If the rms voltage across C is 3V then that across R is:

A. 1 V                                   
B. 3 V
      
C. 2 V                                   
D. 4 V
 

24. The impedance of a circuit consists of 3 resistance and 4
reactance. The power factor of circuits is:

A.  0.4                                    
B.  0.8
         
C.  0.6                                     
D.  1
 

25. According to maximum power transfer theorem, the transfer of
maximum power is only:

A. 25% efficient                       
B. 50% efficient


      
C. 75% efficient                       
D. 100% efficient
 

26. Unit of impedance is:

A. VA-1                                                
B. VA
       
C. V-1 A                               
D. None of these
 

27. In an LCR series circuit, the capacitor is changed from C to 4C. For the same resonant frequency, the inductance should be changed from L to:

A.   2L                                         
B.  L/4
      
C.   L/ 2                                           
D.  4L
 

28. In an A.C circuit, a resistance R is connected in series with an inductance L. If the phase angle between voltage and current be 45, the value of inductive reactance will be:

A.  R/4

     
B.  R

  
   
C.  R/2


      
D. Cannot be found with the given data
 

29. In an A.C circuit containing an inductance and a capacitance in series the current is found to be maximum when the value of inductance is 0.5 henry and capacitanceis 8 F, the angular frequency of the input voltage must be equal to:

A.  500rad/s                                      
B.  4000rad/s
C.  5x10^6rad/s                                
D.  5000rad/s
 

30. The current in resistance at resonance in series resonance circuit
is:

A. Zero                                               
B. Maximum but finite
      
C. Minimum but finite                       
D. Infinite