Nature and power of the corrective lens required to see objects at 25 cm

To determine the nature and power of the corrective lens required by a person to see objects placed at 25 cm from the eye, we need to consider the near point of the eye and the distance of the object from the eye. Here are the steps to find the solution:

Step 1: Understand the concept of near point
The near point of the eye is the minimum distance at which the eye can focus on an object. In this case, the near point is given as 50 cm, which means the person can focus on objects located at a minimum distance of 50 cm from the eye without any corrective lens.

Step 2: Calculate the distance of the object from the near point
To find the distance of the object from the near point, we subtract the distance of the object from the eye (25 cm) from the near point (50 cm):
Distance from near point = Near point - Distance of object
Distance from near point = 50 cm - 25 cm
Distance from near point = 25 cm

Step 3: Determine the nature of the corrective lens required
The nature of the corrective lens required depends on the distance of the object from the near point. If the object is located beyond the near point, a concave lens is needed. If the object is located within the near point, a convex lens is required.

In this case, since the object is located within the near point (25 cm), a convex lens is required to enable the person to see clearly.

Step 4: Calculate the power of the corrective lens
The power of a lens is given by the formula:
Power = 1/Focal Length

The focal length can be calculated using the formula:
Focal Length = 100 cm / Distance from near point

In this case, the distance from the near point is 25 cm. Plugging the value into the formula:
Focal Length = 100 cm / 25 cm
Focal Length = 4 cm

Now, substitute the focal length into the power formula:
Power = 1 / 4 cm
Power = 0.25 D (Diopters)

Therefore, the power of the corrective lens required is +0.25 D, which means a convex lens with a power of +0.25 D is needed for the person to see objects placed at 25 cm from the eye clearly.