For a person near point of vision is 100cm. Then the power of lens he must wear so as to have normal vision, should be

Options

A. `+1 D`
B. `-1 D`
C. `+3 D`
D. `-3D `

Explanation

To solve the problem, we need to determine the power of the lens required for a person whose near point of vision is 100 cm, so that they can see objects clearly at the normal near point of vision, which is 25 cm.

### Step-by-Step Solution:

1. **Understanding the Near Point of Vision**:
- The normal near point of vision for a healthy human eye is approximately 25 cm.
- The person in question has a near point of vision at 100 cm.

2. **Finding the Focal Length of the Lens**:
- To correct the vision, we need to bring the near point from 100 cm to 25 cm.
- We can use the lens formula:
\[ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \]
- Here, \( v \) is the image distance (which will be -25 cm for the normal near point), and \( u \) is the object distance (which will be -100 cm for the person's current near point).

3. **Substituting Values**:
- Convert the distances into meters for calculation:
- \( v = -0.25 \) m (since we take the image distance as negative for virtual images)
- \( u = -1.00 \) m
- Now, substituting the values into the lens formula:
\[ \frac{1}{f} = \frac{1}{-0.25} - \frac{1}{-1.00} \]
- This simplifies to:
\[ \frac{1}{f} = -4 + 1 = -3 \text{ m}^{-1} \]
- Therefore, \( f = -\frac{1}{3} \) m or \( f = -33.33 \) cm.

4. **Calculating the Power of the Lens**:
- The power \( P \) of a lens is given by the formula:
\[ P = \frac{1}{f} \text{ (in meters)} \]
- Since \( f = -\frac{1}{3} \) m:
\[ P = \frac{1}{-\frac{1}{3}} = -3 \text{ diopters} \]

5. **Conclusion**:
- The power of the lens the person must wear to have normal vision is \( -3 \) diopters.

### Final Answer:
The power of the lens he must wear so as to have normal vision should be **-3 diopters**.