Mirrors and Lenses

Page
3

Slide 16

Refraction

Light also goes through some things

glass, water, eyeball, air

The presence of material slows light’s progress

interactions with electrical properties of atoms

The “light slowing factor” is called the index of refraction

glass has n = 1.52, meaning that light travels about 1.5 times slower in glass than in vacuum

water has n = 1.33

air has n = 1.00028

vacuum is n = 1.00000 (speed of light at full capacity)

Slide 17

Refraction at a plane surface

Light bends at interface between refractive indices

bends more the larger the difference in refractive index

Slide 18

Convex Lenses

Thicker in the center than edges.

Lens that converges (brings together) light rays.

Forms real images and virtual images depending on position of the object

The Magnifier

Slide 19

Concave Lenses

Lenses that are thicker at the edges and thinner in the center.

Diverges light rays

All images are erect and reduced.

The De-Magnifier

Slide 20

How You See

Near Sighted – Eyeball is too long and image focuses in front of the retina

Near Sightedness – Concave lenses expand focal length

Far Sighted – Eyeball is too short so image is focused behind the retina.

Far Sightedness – Convex lense shortens the focal length.

Slide 21

Cameras, in brief

In a pinhole camera, the hole is so small that light hitting any particular point

on the film plane must have come from a particular direction outside the camera

In a camera with a lens, the same applies: that a point on the film plane

more-or-less corresponds to a direction outside the camera. Lenses have

the important advantage of collecting more light than the pinhole admits