Refraction, Lenses, & Sight

• Copy all text underlined in red. Draw

sketches outlined in red.

Refraction • The change in direction of a wave as is crosses the

boundary between two media in which the wave

travels at different speeds.

Index of Refraction

materialinlightofspeed

vacuuminlightofspeedn

Snell’s Law 2211

sinsin nn

Index of Refraction Material Index of Refraction

Vacuum 1.0000

Air 1.0003

Ice 1.3100

Water 1.3330

Ethyl Alcohol 1.3600

Plexiglas 1.5100

Crown Glass 1.5200

Light Flint Glass 1.5800

Dense Flint Glass 1.6600

Zircon 1.9230

Diamond 2.4170

Rutile 2.9070

Gallium phosphide 3.5000

Dispersion

• The separation of light into colors arranged

according to their frequency, by interaction

with a prism or diffraction grating.

Rainbows • White light separates into different colors

(wavelengths) on entering the raindrop because red light is refracted by a lesser angle than blue light. On leaving the raindrop, the red rays have turned through a smaller angle than the blue rays, producing a rainbow.

STOP HERE

Lenses

Converging Lens

Rules For Converging Lenses

1) Any incident ray traveling parallel to the

principal axis of a converging lens will refract

through the lens and travel through the focal

point on the opposite side of the lens.

2) Any incident ray traveling through the focal

point on the way to the lens will refract through

the lens and travel parallel to the principal axis.

3) An incident ray which passes through the center

of the lens will in effect continue in the same

direction that it had when it entered the lens.

Image Formation by Converging Lens

Diverging Lens

Rules For Diverging Lenses

1) Any incident ray traveling parallel to the

principal axis of a diverging lens will refract

through the lens and travel in line with the focal

point (i.e., in a direction such that its extension

will pass through the focal point).

2) Any incident ray traveling towards the focal

point on the way to the lens will refract through

the lens and travel parallel to the principal axis.

3) An incident ray which passes through the center

of the lens will in effect continue in the same

direction that it had when it entered the lens.

Diverging Lens Image Formation

Always Virtual, Smaller, and Right-Side Up

The Human Eye

The Human Eye

Normal Eye Focus

Near-Sighted (Myopia)

Far-Sighted (Hypermetropia)

Astigmatism

• Cornea is oval shaped instead of spherical.

This causes light to focus on two or more

spots.

LASIK

Laser-assisted In Situ Keratomileusis