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

Options

A. If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
B. If both Assertion and Reason are true but Reason is not correct explanation of Assertion.
C. If Assertion is true but Reason is false.
D. If Assertion is false but Reason is true.

Answer

To solve the question regarding the assertion and reason about the lens formula, we can break it down step by step.

### Step 1: Understand the Assertion
The assertion states that the lens formula can be applied only for thin lenses. The lens formula is given by:

\[ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \]

where:
- \( f \) = focal length of the lens
- \( v \) = image distance
- \( u \) = object distance

### Step 2: Analyze Thin Lenses
In thin lenses, the thickness is negligible compared to the radius of curvature. This means that light rays refract at only one surface of the lens, allowing us to use the simple lens formula effectively.

### Step 3: Understand the Reason
The reason states that for thick lenses, one cannot find the image position. This is misleading. While the lens formula is not directly applicable to thick lenses, it is still possible to find the image position using more complex formulas that account for the thickness of the lens.

### Step 4: Conclusion
- The assertion is **true**: The lens formula is primarily applicable to thin lenses.
- The reason is **false**: It is indeed possible to find the image position for thick lenses, although the method is more complicated.

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

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