Optics mirrors & lenses

1. OpticsOptics

2. 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 includingThis includes it’s interactions with objects including
mirrors, lenses, and substances which reflect or scattermirrors, lenses, and substances which reflect or scatter
light.light.

3. When Light Strikes an ObjectWhen Light Strikes an Object
•When light strikes an object, theWhen light strikes an object, the
light can be reflected, transmitted,light can be reflected, transmitted,
scattered, or absorbed.scattered, or absorbed.

4. MirrorsMirrors
•Have you ever gone to the fun houseHave you ever gone to the fun house
and looked at yourself in the manyand looked at yourself in the many
different mirrors there?different mirrors there?
•Have you ever wondered how theHave you ever wondered how the
image forms?image forms?
•The image formed is a result ofThe image formed is a result of
reflection, which you learned about inreflection, which you learned about in
the previous unit.the previous unit.
•There are three types of mirrors: plane,There are three types of mirrors: plane,
concave, and convex.concave, and convex.
•A plane mirror is a flat mirrorA plane mirror is a flat mirror
Plane mirror

5. 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
same
angleincident ray exit ray
reflected ray

6. 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

7. RefractionRefraction
• Light also goesLight also goes throughthrough some thingssome 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 theThe “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)

8. Refraction of LightRefraction of Light
(not reflection)(not reflection)
•When light rays enter a medium at an angle, theWhen light rays enter a medium at an angle, the
change in speed causes the rays to bend or changechange in speed causes the rays to bend or change
direction.direction.

9. 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

10. 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

11. - Refraction and Lenses
LensesLenses
•AA lenslens is a curved piece of glass or other transparentis a curved piece of glass or other transparent
material.material.

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

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

14. What is polarization?What is polarization?
• The vibrations are limited to just one direction in aThe 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 theThus, 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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15. Few related lawsFew related laws
• Malus lawMalus law
• States that : when a beam of completely planeStates that : when a beam of completely plane
polarized light is incident on an analyser, thepolarized light is incident on an analyser, the
resultant intensity of light (I) transmitted from theresultant intensity of light (I) transmitted from the
analyser varies directly and the square of the cosineanalyser 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
polariserpolariser
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16. Malus lawMalus law
• Intensity emerging from polarizer isIntensity emerging from polarizer is
IIααEE22
• Intensity emerging from analyserIntensity emerging from analyser
II θθ αα EE22
coscos22
• Dividing 2 by 1Dividing 2 by 1
• We get IWe get I θθ = I cos= I cos22
θθ
• So whenSo when θθ=90 , transmission axis of polariser and=90 , transmission axis of polariser and
analyser is perpendicularanalyser is perpendicular
II θθ = 0.= 0.
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17. Magnification or ReductionMagnification or Reduction