Learn how the eye focuses light, common vision defects and their correction, and why the sky is blue and sunsets are red.
The eye lens focuses light onto the retina. The ciliary muscles change the lens's shape to focus on objects at different distances — this is called accommodation.
What is the normal near point (closest comfortable focusing distance) of the human eye?
25 cm
What is the name for the eye's ability to adjust its lens shape to focus on near and far objects?
Accommodation
Distant objects appear blurry. Corrected with a concave (diverging) lens.
Nearby objects appear blurry. Corrected with a convex (converging) lens.
A person can see distant objects clearly but not nearby ones. What defect is this, and what lens corrects it?
Hypermetropia (farsightedness) — corrected with a convex lens
Tiny particles in the atmosphere scatter shorter wavelengths of light (blue) more than longer wavelengths (red).
Why does the sky appear blue during the day?
Blue light has a shorter wavelength and is scattered much more than red light by the atmosphere's particles, filling the sky with scattered blue light
Why does the sun appear reddish at sunrise and sunset?
Sunlight travels through more atmosphere at a low angle, scattering away most of the blue light before it reaches your eyes, leaving mostly red/orange
1. What is the normal near point distance of the human eye?
2. Which lens type corrects myopia (nearsightedness)?
3. Which lens type corrects hypermetropia (farsightedness)?
4. Which colour of light is scattered the most by the atmosphere: red or blue?
5. Why does a clear sky look black from space, with no atmosphere to scatter light?