Geometric Optics Topics include reflection, refraction, lenses & mirrors and how images are formed, magnification

Reflection and refraction Ray model of light ….. Light travels in straight lines…..like a lazer pointer For light reflecting off of a mirror, the incident angle = reflected angle

Image formed for a flat mirror The image formed in a flat plane mirror appears to be the same distance into the mirror that the object is in front of the mirror.

Refraction and Snell’s Law When light travels between 2 different transparent materials (like air and water….or pancake syrup and glass) it bends. This bending of light occurs because the speed of the light changes. The index of refraction, n , tells you how much the light slows down compared with the speed of light in a vacuum. n = c/v c = 3 x 10E8 and v = velocity in that material. n = 1 in air n = 1.33 for water, n= 1.5 Log cabin

So light bends when it hits an interface at an angle… So light bends when it hits an interface at an angle….what direction does it bend? Use the little red wagon analogy of science……. Refraction

Refraction Snell’s law allows you to calculate the angle that light bends…… ninsinΘin = noutsinΘout Say light in air is incident on a slab of glass at an incident angle of 30 degrees. What is the angle in the glass?

Refraction and Total internal Reflection When light travels from slow material (like glass) to a faster material (like air) it bends away from the normal line. Because of this property there is a condition that light incident on a surface can never “get out” . We call this total internal reflection. The minimum incident angle for this is called the critical angle….this happens when the angle out is 90 degrees. (next slide….example)

Total Internal Reflection and the Critical Angle When light travels from “slow” material to “fast” material it can get trapped in the slow material.

Refraction and Total internal Reflection Say light is traveling in plastic (n = 1.4) which is in air. What is the critical angle at which all of the light would be totally internally reflected? For the idea of the critical angle, the outgoing angle is ALWAYS 90 degrees!