Assertion :- Lens formula can be applied only for thin lenses
Reason :- For thick lenses one cannot find image position.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False.

Answer

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

**Assertion:** Lens formula can be applied only for thin lenses.

**Reason:** For thick lenses, one cannot find the image position.

### Step-by-step Solution:

1. **Understanding the Lens Formula:**
The lens formula is given by:
\[ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \]
where \( f \) is the focal length, \( v \) is the image distance, and \( u \) is the object distance. This formula is primarily derived under the assumption that the lens is thin.

2. **Thin vs. Thick Lenses:**
- **Thin Lenses:** The lens is considered thin when the thickness of the lens is negligible compared to the focal length. In this case, the lens formula can be applied directly.
- **Thick Lenses:** For thick lenses, the situation is more complex due to the additional effects of the lens thickness on light refraction. However, it is still possible to find the image position using more complex formulas that account for the thickness.

3. **Analyzing the Assertion:**
The assertion states that the lens formula can be applied only for thin lenses. This is partially true, as the simple lens formula is derived for thin lenses. However, it can also be modified for thick lenses.

4. **Analyzing the Reason:**
The reason states that for thick lenses, one cannot find the image position. This is false because while the calculations are more complex, it is indeed possible to find the image position for thick lenses using appropriate formulas.

5. **Conclusion:**
- The assertion is true in the sense that the simple lens formula is primarily applicable to thin lenses.
- The reason is false because image positions can be determined for thick lenses, although it requires more complex calculations.

### Final Answer:
The correct option is **C**: The assertion is true, but the reason is false.

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