Assertion : In a practical choke coil, power factor is very small.
Reason : In a practical choke coil, heat dissipation reduces when frequency of AC source is increased.

Options

A. If both assertion and reason are correct and reason is a correct explanation of the assertion
B. If both assertion and reason are correct but reason is not the correct explanation of assertion
C. If assertion is correct but reason is incorrect
D. If assertion is inncorrect but reason is correct

Answer

To solve the question, we need to analyze the assertion and reason provided:

**Assertion:** In a practical choke coil, the power factor is very small.

**Reason:** In a practical choke coil, heat dissipation reduces when the frequency of the AC source is increased.

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- A choke coil, which is essentially an inductor, has a very low resistance (R) compared to its reactance (XL) at typical operating frequencies.
- The power factor (PF) is defined as the cosine of the phase angle (φ) between the voltage and current, which can be expressed as:
\[ \text{Power Factor} = \cos \phi = \frac{R}{Z} \]
- Here, Z is the impedance given by:
\[ Z = \sqrt{R^2 + (X_L - X_C)^2} \]
- Since R is very small, the power factor becomes very small, confirming that the assertion is correct.

2. **Understanding the Reason:**
- The reason states that heat dissipation reduces when the frequency of the AC source is increased.
- Heat dissipation (H) in a resistive circuit can be expressed as:
\[ H = I_{\text{rms}}^2 \cdot R \cdot T \]
- Where \( I_{\text{rms}} \) is the root mean square current, which can be expressed as:
\[ I_{\text{rms}} = \frac{V_{\text{rms}}}{Z} \]
- As the frequency increases, the reactance (XL) increases, which affects the impedance (Z) and consequently the current (I).
- If the frequency increases, the impedance Z increases (due to XL), leading to a decrease in \( I_{\text{rms}} \). Therefore, the heat dissipation (H) decreases as the frequency increases.
- This means the reason is also correct.

3. **Conclusion:**
- Both the assertion and reason are correct. However, the reason does not provide a correct explanation for the assertion. The assertion is based on the low resistance leading to a low power factor, while the reason discusses heat dissipation without directly linking it to the power factor.

### Final Answer:
- The correct option is that both the assertion and reason are correct, but the reason is not the correct explanation of the assertion.