how can we estimate the power of normal eye when it is looking at the moon???

The power of the eye = 1/focal length.

Since looking at distant objects like moon, the incoming rays are parallel to each other and are focused on the retina.

The distance between the image which is formed on retina from the lens is 4 cm.

While the object distance is infinite.

Substituting this in the lens formula, given the focal length as 4 cm.

Hence the power is 0.25 cm^-1

Regards,

Team,

TopperLearning.