The magnification power of a convex lens of focal length 10cm, when the image is formed at the near point is

Options

A. 6
B. 5.5
C. 4
D. 3.5

Explanation

To find the magnification power of a convex lens with a focal length of 10 cm when the image is formed at the near point, follow these steps:

### Step 1: Understand the Concept of Near Point
The near point (the closest distance at which the eye can comfortably see an object) is typically taken as 25 cm for a normal human eye.

### Step 2: Use the Magnification Formula
The magnification (M) produced by a lens can be calculated using the formula:
\[ M = 1 + \frac{D}{f} \]
where:
- \( D \) is the distance of the near point (25 cm),
- \( f \) is the focal length of the lens (10 cm).

### Step 3: Substitute the Values
Substituting the values into the formula:
\[ M = 1 + \frac{25 \text{ cm}}{10 \text{ cm}} \]

### Step 4: Calculate the Fraction
Calculate the fraction:
\[ \frac{25}{10} = 2.5 \]

### Step 5: Add to 1
Now, add 1 to the result:
\[ M = 1 + 2.5 = 3.5 \]

### Step 6: Conclusion
Thus, the magnification power of the convex lens when the image is formed at the near point is:
\[ M = 3.5 \]

### Final Answer
The correct option is 3.5.

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