Question

Which of the following combination should be selected for better turning of an L.C.R circuit used for communication?

• A. $R=25\Omega ,L=1\cdot 5H,C=45\mu F$
• B. $R=25\Omega ,L=1\cdot 5H,C=35\mu F$
• C. $R=25\Omega ,L=2\cdot 5H,C=45\mu F$
• D. $R=15\Omega ,L=3\cdot 5H,C=30\mu F$

Answer 1

Answer: (D)

$R=15\Omega ,L=3\cdot 5H,C=30\mu F$

For tuning an LCR circuit, its selectivity should be high. High selectivity is observed in circuits with high-quality factor.

$Q=\frac{\sqrt{L}}{R\sqrt{C}}$

Puting value in above equation:
For option (a), $Q=7.3$

For option (b), $Q=8.28$

For option (c), $Q=9.43$

For option (d), $Q=13.67$

As $Q=\frac{\sqrt{3.5}}{15\sqrt{30\times {10}^{-6}}}=13.67$

Hence, option (d) is the best combination.