Human Eye And Colorful World Flashcards
Diameter of eyeball
2.3 cm
Cornea
Outermost transparent bulge, thin membrane
Most refraction occurs at its surface
Crystalline lens
Fibrous Jelly like material, convex lens
Provids finer adjustment of focal length
Iris
Dark muscular diaphragm
Controls side of the pupil
Pupil
Central aperture in the iris
Regulates the amount of light entering the eye
Retina
Delicate membrane with light sensitive cells
Briefly explain how we are able to see things
Light reaches retina
Light sensitive cells get activated upon illumination and generate electrical signals
Signals reach brain via optic nerves
Brain processes signals and we see
Ciliary muscle function
Change the curvature of eye lens and hence its focal length
Accommodation of eye, definition
The ability of the eye lens to adjust its focal length
When object is close, do ciliary muscles contract or relax?
Contract, decrease focal length
Define near point
The minimum distance at which we can see objects clearly withour strain
About 25 cm
Define far point
Farthest distance we can see objects clearly
Infinity
What is a cataract
When crystalline lens becomes milky and cloudy often at old age
Causes partial or complete loss of vision
Why do we have two eyes
Wider field of view: 150 vs 180 degrees
Stereopsis: depth, combines two images to understand how far things are
Myopia
Definition + cause + correction
Near sightedness
Cannot see distant objects clearly
Aka far point nearer than infinity
Image is formed in front of retina
Excessive curvature of eye lens
Elongation of eyeball
Concave lens
Hypermetropia
Definition + cause + correction
Far sightedness
Cannot see nearby objects clearly
Near point is farther than 25 cm
Image formed behind retina
Focal length is too long
Eyeball becomes small
Convex lens
Presbyopia
Similar to hypermetropia except cause is old age
Near point gradually recedes with time due to gradual weakening of ciliary muscles and flexibility of eye lens
Bi focal lens
For people with both myopia and hypermetropia
Upper portion concave
Lower portion convex
What is a prism
Two triangular bases and three rectangular lateral surfaces
Dispersion, who was the first to obtain it with a prism
The spitting of white light into into its component colours
Isaac newton
How are rainbows formed
Dispersion of sunlight by water droplets
Refract and disperse > reflect it internally > refract it again when it comes out
Always formed in direction opposite to the sun
Explain the flickering/wavering above fire
Hotter air is less dense (and hence has a lesser refractive index) than cooler air above.
Hot air rises and cool air also moves, so the refractive index fluctuates
Why do stars twinkle? Why not planets?
Star light refracts continuously in the atmosphere. The refractive index gradually changes.
Hence atmospheric refraction bends starlight towards normal and its apparent position appears slightly lower.
Atmosphere is not stationary so the path of light always varies slightly, and the amount of starlight entering the eye varies: brighter/fainter. Twinkling effect.
Planets are much larger, variation in amount of light entering our eyes is negligible
How does atmospheric refraction effect sunrise senset
Sunrise 2 minutes early
Sunset 2 minutes late
Sun appears higher than actual position, like stars
Tyndall effect
What is scattering of light
Spreading of light in various directions by colloid particles (when light deviates from its straight path)
When light passes through a colloid, its path becomes visible
Ex, dust, dense canopy water droplets in misy
Why is the sky blue
Molecules of air etc are smaller than the wavelength of visible light
These are more effective in scattering light of shorter wavelength (blues) than longer wavelength (red)
If earth had no atmosphere
No scattering of light would take place, dark
Example passengers at high altitudes see a dark sky as atmosphere is thinner and scattering is less prominent
Why are danger signals red
Red is least scattered by fog smoke etc, it can be seen as red from a distance
Why are clouds white
Water/ice/dust droplets are large, all colors of light are scattered, they appear white
Why does sunrise/sunset appear red
Sun is near the horizon hence it travels a larger distance in the atmosphereand thick layers of atmosphere
Short wavelength (blues) is scattered away and long wavelength (reds) reaches our eyes
At noon, the sky is almost white
Sunlight travels least distance, only a little bit of blues (short wavelength) is scattered
