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

Options

A. R = 25 ohm, L = 1.5H, C = 45 microF
B. R = 25 ohm, L = 1.5H, C = 35 microF
C. R = 25 ohm, L = 2.5H, C = 45 microF
D. R = 25 ohm, L = 3.5H, C = 30- microF

Answer

To determine the best combination for better tuning of an L.C.R circuit used for communication, we need to analyze the Q factor of the circuit. The Q factor is a measure of the sharpness of the resonance of the circuit, and a higher Q factor indicates better tuning.

### Step-by-Step Solution:

1. **Understanding the Q Factor**:
The Q factor (Quality factor) of an L.C.R circuit is given by the formula:
\[ Q = \frac{1}{R} \sqrt{\frac{L}{C}} \]
Where:
- \( Q \) is the quality factor,
- \( R \) is the resistance,
- \( L \) is the inductance,
- \( C \) is the capacitance.

2. **Analyzing the Factors**:
From the formula, we can see that:
- \( Q \) is inversely proportional to \( R \): As \( R \) decreases, \( Q \) increases.
- \( Q \) is directly proportional to \( \sqrt{L} \): As \( L \) increases, \( Q \) increases.
- \( Q \) is inversely proportional to \( \sqrt{C} \): As \( C \) decreases, \( Q \) increases.

3. **Choosing the Best Combination**:
To maximize the Q factor, we need:
- Low resistance \( R \),
- High inductance \( L \),
- Low capacitance \( C \).

4. **Evaluating the Options**:
We need to evaluate the given options based on the criteria above. We will check the values of \( R \), \( L \), and \( C \) in each option to determine which combination yields the highest Q factor.

5. **Final Decision**:
After evaluating all four options, we find that the fourth option has the lowest capacitance \( C \) while maintaining a reasonable inductance \( L \) and resistance \( R \). Therefore, the fourth option provides the best combination for better tuning of the L.C.R circuit.

### Conclusion:
The best combination for better tuning of an L.C.R circuit used for communication is **Option 4**.

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