UCSD Physics 10

UCSD Physics 10

UCSD Physics 10

3Winter 2004

Reflection• Reflection off a flat surface follows a simple LAW OF REFLECTION :

– angle in (incidence) equals angle out– angles measured from surface “normal” (perpendicular)

surface normal

sameangleincident ray exit ray

UCSD Physics 10

4Winter 2004

Hall Mirror• It is useful to think in terms of images and objects

“image” of you

The real “object” (you)

mirror onlyneeds to be half as

high as you are tall. Yourimage will be twice as far from you

as the mirror.

UCSD Physics 10

UCSD Physics 10

6Winter 2004

Refraction

• Light also goes through some things– glass, water, eyeball, air

• Presence of material slows light’s progress– interactions with electrical properties of atoms

• Light has slowing and bending factor called the index of refraction. The denser it is the higher the index and the more it slows and bends light – 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)

UCSD Physics 10

7Winter 2004

• The index of refraction tells how many times slower an object travels when passing into the denser substance

Find the speed of light through corn oil .

UCSD Physics 10

8Winter 2004

n2 = 1.5n1 = 1.0

A

B

Refraction at a plane surface• Light bends at interface between refractive indices

1

2

UCSD Physics 10

When light goes into a denser material it bends ____________the normal

When light goes into a less dense material it bends ____________the normal

UCSD Physics 10

UCSD Physics 10

Snell’s Law

UCSD Physics 10

12Winter 2004

Snell’s Law