Question

The maximum focal length of the eye-lens of a person is greater than its distance from the retina. The eye is:
A) Always strained at looking at an object
B) Strained for looking at large distance only
C) strained for object at short distance only
D) unstrained for all distances.

Answer 1

Hint: We know that the human eye lens can change its focal length according to the distance of the object. Now, we know that all the objects are at different distances from each other, which means, our eye has to change the focal length of the lens every time. We just have to know what is the effect of this change in focal length on our eyes.

Complete step by step solution:
Let us take all the options one by one and then analyze them,
Option A: We know that all the objects are at varying distances from each other, which means, our eye has to change the focal length of the lens every time. So, we can say that our eyes are always strained in looking at an object
Hence, it is the correct option.

Option B: Now, this option states that human eyes only get strained when looking at an object which is at a large distance but as we have discussed in option A, the human eye gets strained for looking at an object even if it is very close to our eyes.
Hence, this option is incorrect.

Option C: Now, this option states that human eyes only get strained when looking at an object which is at a short distance but as we have discussed above, the human eye gets strained for looking at an object which is very far from away from the eyes.
Hence, this option is also incorrect.

Option D: As we have discussed above, all the objects are at different distances from each other and also at different distances from our eyes, which means, our eye has to change the focal length of the lens every time to see them. So, we can say that our eyes are always strained. Hence, this option is also incorrect.

So, the correct answer is option (A).

Note: We know that the human eye lens is a convex lens and it converges the rays of the lights to fall on the retina. Now, to see a clear image, the eye lens has to decrease and increase its focal length for far and near objects respectively. Hence, the human eye always gets strained looking at both near and distant objects.