Question

Range of vision of a normal human eye is from:
A. $100$ m to $25$ cm
B. $1$ km to $25$ cm
C. Infinity to $25$ m
D. Infinity to $25$ cm

Answer 1

Hint: Human eye, an amazing optical instrument in humans. The human eye reacts with light and allows us to see the world. The first step in formation of an image in our eyes is passing light through the cornea. The pupil of the eye allows the light to enter in the eye and iris controls the amount of light allowed to enter by pupil of the eye. The light then passes through the lens of the eye and then the light hits the retina of our eyes. In the human eye, the image is formed on the retina and the image formed is inverted. The inverted image is corrected by our brain by sending electrical signals from the retina to the brain.

Complete answer:
For a normal human eye, the range of vision describes the range of distance for which human eyes can see an object clearly. For a person to see an object with a clear vision, the image of that object must fall accurately on the retina. This means that the distance of image must be equivalent to that of lens-to retina distance. But, the lens-to-retina distance remains fixed, therefore the image distance is always the same for all objects at all distances. Our eyes manage to do this by adjusting the power of their lenses. This process of adjustment is known as accommodation and it is done by changing the shape of the lens of our eyes.

To form a clear image of an object, the nearest point at which it can be placed is called the near point of the eye. For an object to be clearly visible from far distance, the farthest point at which it needs to be placed and the point is termed as the far point of the eye. For a normal human eye, the range of vision is between infinity and $25$ cm. This is the distance between the far and near point of the human eye.

Therefore, the correct option is option D.

Note: Students may think that seeing a distant object through our eyes is more tiring for our eyes than seeing an object placed very close to our eyes. But, this is not true. While seeing an object placed closer to our eyes, the lens in our eyes need to be more powerful or converging because the light rays from a closer object can diverge and enter our eyes. To become more powerful, the lens of our eyes should be thicker and this can be achieved by the ciliary muscles present in our eyes near the lens. On the other hand, while seeing a distant object our eyes are more relaxed and it is focused on infinity.