OpticsOptics

OpticsOptics

•OpticsOptics is the study of the behavior and properties of light. is the study of the behavior and properties of light.

•This includes it’s interactions with objects including mirrors, This includes it’s interactions with objects including mirrors, lenses, and substances which reflect or scatter light.lenses, and substances which reflect or scatter light.

When Light Strikes an ObjectWhen Light Strikes an Object

•When light strikes an object, the When light strikes an object, the light can be reflected, transmitted, light can be reflected, transmitted,

scattered, or absorbed.scattered, or absorbed.

Mirrors Mirrors •Have you ever gone to the fun house and looked at yourself in the many different mirrors there? Have you ever gone to the fun house and looked at yourself in the many different mirrors there?

•Have you ever wondered how the image forms? Have you ever wondered how the image forms?

•The image formed is a result of reflection, which you learned about in the previous unit. The image formed is a result of reflection, which you learned about in the previous unit.

•There are three types of mirrors: plane, concave, and convex. There are three types of mirrors: plane, concave, and convex. •A plane mirror is a flat mirror A plane mirror is a flat mirror

•  

Plane mirror

ReflectionReflection• We describe the path of light as straight-line raysWe describe the path of light as straight-line rays• Reflection off a flat surface follows a simple rule:Reflection off a flat surface follows a simple rule:

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

surface normal

sameangleincident ray exit ray

reflected ray

Reflection VocabularyReflection Vocabulary• Real Image – Real Image –

–Image is made from “real” light rays that converge at a real focal point so the image is REAL

–Can be projected onto a screen because light actually passes through the point where the image appears

–Always inverted

RefractionRefraction• Light also goes Light also goes throughthrough some things some things

– glass, water, eyeball, air

• The presence of material slows light’s progressThe presence of material slows light’s progress– interactions with electrical properties of atoms

• The “light slowing factor” is called the The “light slowing factor” is called the index of refractionindex 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)

Refraction of Light Refraction of Light (not reflection)(not reflection)

•When light rays enter a medium at an angle, the When light rays enter a medium at an angle, the change in speed causes the rays to bend or change change in speed causes the rays to bend or change direction.direction.

n2 = 1.5

n1 = 1.0

A

B

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

– bends more the larger the difference in refractive index

n2 = 1.5

n1 = 1.0

A

B

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

– bends more the larger the difference in refractive index

- Refraction and Lenses

LensesLenses

•A A lenslens is a curved piece of glass or other transparent is a curved piece of glass or other transparent material.material.

LensesLenses•An object’s position relative to the focal point An object’s position relative to the focal point determines whether a convex lens forms a real image determines whether a convex lens forms a real image or a virtual image.or a virtual image.

LensesLenses

•A concave lens can produce only virtual images A concave lens can produce only virtual images because parallel light rays passing through the lens because parallel light rays passing through the lens never meet.never meet.

What is polarization?What is polarization?

• The vibrations are limited to just one direction in a The vibrations are limited to just one direction in a plane perpendicular to the direction of propagation, plane perpendicular to the direction of propagation, the wave is said to be plane polarizedthe wave is said to be plane polarized

• Thus, the phenomenon of the restriction of the Thus, the phenomenon of the restriction of the vibration to a particular direction is called polarizationvibration to a particular direction is called polarization

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Few related lawsFew related laws

• Malus lawMalus law• States that : when a beam of completely plane States that : when a beam of completely plane

polarized light is incident on an analyser, the polarized light is incident on an analyser, the resultant intensity of light (I) transmitted from the resultant intensity of light (I) transmitted from the analyser varies directly and the square of the cosine analyser varies directly and the square of the cosine angle (angle (θθ) betn plane of transmission of analyser and ) betn plane of transmission of analyser and polariser polariser

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Malus lawMalus law

• Intensity emerging from polarizer isIntensity emerging from polarizer is

IIααEE22

• Intensity emerging from analyserIntensity emerging from analyser

I I θθ αα E E22 cos cos22

• Dividing 2 by 1Dividing 2 by 1

• We get I We get I θθ = I cos = I cos22 θθ• So when So when θθ=90 , transmission axis of polariser and =90 , transmission axis of polariser and

analyser is perpendicularanalyser is perpendicular

I I θθ = 0.= 0.

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Magnification or ReductionMagnification or Reduction