# Lecture 6 - Lecture 6 > Optics > Reflection ... Ray Optics 2 > Light travels in straight lines > Light

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• Lecture 6

> Optics

> Reflection & Refraction

Giancoli, Physics 6/e Serway & Vuille, College Physics 8/e Serway & Jewett, Physics for Scientists & Engineers, 6/e Tippens, Physics 7/e Young, Freedman & Ford, University Physics 14/e

1 Villacorta--DLSUM-SCITECS-L06-1718Term03

• Ray Optics

2

> Light travels in straight lines

> Light propagation can be illustrated using rays, showing their direction as it travels through space.

> Geometric optics refers to studying light propagation using the rays and angles

Villacorta--DLSUM-SCITECS-L06-1718Term03

• Reflection

3

> Shiny objects reflect light that hits it

> Angle of incidence, angle of reflection + Light bounces back at the same angle that it hit the object + Optical plane + Surface normal + Law of reflection

> Types of reflections + Diffuse: scattered, uneven, rough surface + Specular: mirror, image formation

> Images: plane mirrors + Virtual image: can't be projected + Real image: can be projected

Villacorta--DLSUM-SCITECS-L06-1718Term03 Johan Arvelius https://en.wikipedia.org/wiki/File:Reflection_angles.svg

• Refraction

4

> Light travels slower through a medium than through vacuum: the ratio of these speeds is the index of refraction of the material

n= c

v

boomeria.org

Villacorta--DLSUM-SCITECS-L06-1718Term03 https://en.wikipedia.org/wiki/File:Snells_law.svg

• Refraction contd.

5

> When light passes through a material, it bends due to traveling at a different speed: the relationship is given by Snell's law

Willebrord Snellius 1580-1626

wikipedia.orgagilescientific.com

n1 sin θ1=n2 sin θ2

Villacorta--DLSUM-SCITECS-L06-1718Term03

• Total Internal Reflection

6

> When light goes from a slow medium to a fast one, it is possible for the light to be reflected inward and NOT refract into the second faster medium.

> This occurs at a given critical angle θ C

for material

> Fiber optic cables work in this manner.

ualberta.caVillacorta--DLSUM-SCITECS-L06-1718Term03

• Ray Tracing

7

> Images are formed by light rays intersecting + Real image: intersection of reflected or refracted light rays + Virtual images: intersection of the projections of reflected or refracted light rays

> The place where the image will form is the image distance: + It can be farther + or nearer to the mirror or lens

> The image can also be: + Magnified + or shrunk

Villacorta--DLSUM-SCITECS-L06-1718Term03

• Mirrors

8

> The principal axis goes through the center of the mirror.

> The center represents the center of a circle that the mirror is part of.

> The focus is approximately located halfway between the center and the mirror.

langlopress.net

> Light rays passing through the center bounce off the mirror, passing through the center again.

> Light rays passing through the focus bounce off the mirror, parallel to the principal axis.

> Light rays initially parallel to the principal axis bounce off the mirror passing through the focus.

Villacorta--DLSUM-SCITECS-L06-1718Term03

• Mirrors contd.

9

* q > 0 if the reflected or refracted rays are on the same side as the focus

* q < 0 if the reflected or refracted rays are on the opposite side as the focus

langlopress.net

1

p +

1

q =

1

f

m= image ht

object ht =

�q

s

Villacorta--DLSUM-SCITECS-L06-1718Term03

• Mirrors contd.

10

* q > 0 if the reflected or refracted rays are on the same side as the focus

* q < 0 if the reflected or refracted rays are on the opposite side as the focus

langlopress.net

1

p +

1

q =

1

f

m= image ht

object ht =

�q

s

Villacorta--DLSUM-SCITECS-L06-1718Term03

• Summary

11

> Light travels in straight lines

> Light can be reflected off a surface or refracted through a medium

Mirrors can make images from light rays that bounce off it

Villacorta--DLSUM-SCITECS-L06-1718Term03

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