Q.

Which of the following combinations should be selected for better tuning of an L-C-R circuit used for communication          [2016]
 

1 R=20Ω,L=1.5H,C=35μF  
2 R=25Ω,L=2.5H,C=45μF  
3 R=15Ω,L=3.5H,C=30μF  
4 R=25Ω,L=1.5H,C=45μF  

Ans.

(3)

Quality factor of an L-C-R circuit is given by,

Q=1RLC

Q1=1201.535×10-6=50×370=10.35

Q2=125×2.545×10-6=40×590=9.43

Q3=1153.530×10-6=10015353=22.77

Q4=125×1.545×10-6=4030=7.30

Clearly Q3 is maximum of Q1,Q2,Q3, and Q4.

Hence, option (3) should be selected for better tuning of an L-C-R circuit.