chapter 34 geometric optics

7/24/2019 Chapter 34 Geometric Optics

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Geometric Optics

Chapter 34

1Physics 72 Bareza AY 15-16 1st sem


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Chapter 34Geometric Optics

34-1 Reflection and Refraction at a Plane Surface

34-2 Reflection at a Spherical Surface

34-3 Refraction at a Spherical Surface

34-4 Thin Lens

2 Physics 72 Bareza AY 15-16 1st sem


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Reflection and Refraction at a Plane Surface34-1

OBJECTIVES

Given an object in front of a plane mirror:Calculate the location of the image

Calculate the lateral magnification of the image

Determine whether the image will be real or virtual, and uprightor inverted

Physics 72 Bareza AY 15-16 1st sem


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What is an object?anything from which light rays radiate

light could be emitted by the

object itself

light could be emitted by another

source and then reflected from theobject


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1. Point Object no physical extent

2. Extended Object real object with length, width and height

Point object Pmade up of a very largenumber ofpoint objects


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What is an image? from which outgoing rays diverge


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An image can be:

1. Real image outgoing rays really do pass through an image point


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An image can be:

2. Virtual image outgoing rays don't actually pass through the image point


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1. Sign rule for the

object distance s

When the object is on thesame side of the reflecting or

refracting surface as the

incoming light, the object

distance sis positive;

otherwise, it is negative.

Sign Rules

sis positive.


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image distance s

When the image is on thesame side of the reflecting or

refracting surface as the

outgoing light, the image

distance s' is positive;

otherwise, it is negative.

Sign Rules

s is negative.


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radius of curvature R

of a spherical surface: When the center of curvature C is

on the same side as the

outgoing light, the radius of

curvature is positive; otherwise,

it is negative.

Sign Rules

For a plane reflecting or refracting

surface, Ris infinite.


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Plane Mirror: Image of a Point ObjectReflection

Note: s is negative

image is virtual


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Plane Mirror: Image of an Extended ObjectReflection

where: y : object height

y : image height

s : object distance

s: image distance

The image formed by a plane mirror is always erect (y > 0).


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Lateral Magnification


y : image height s : object distance

s : image distance

If m > 0: image orientation same with that of object

If m< 0: image orientation different from that of object

If y > 0: image uprightIf y < 0: image inverted

If s > 0: image real

If s < 0: image virtual

Sign Conventions:

If |m| > 1: magnified

If |m| < 1: reduced

If |m| = 1: same size


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y : image height

s : object distance

s : image distance

Plane MirrorReflection

Lateral Magnification


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Example:


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Example:


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Seatwork:A bug at about eye level is 5 cm in front of a plane mirror. You

are behind the bug, 20 cm from the mirror. What is the

distance between your eyes and the apparent position ofthe bugs image in the mirror?


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34-3 Refraction at a Spherical Surface34-4 Thin Lens

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Reflection at a Spherical Surface34-2

OBJECTIVES

Given an object in front of a spherical mirror:

Calculate the location of the imageCalculate the lateral magnification of the image


Given an object placed in front of a spherical mirror, drawthe principal rays and locate the image



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Convex Mirror Concave Mirror


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Concave Mirror:Point object

C R> 0

Voptic axis Object P

Image P

s > 0

s> 0


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Physics 72 Bareza AY 15-16 1st sem s> 0

Concave Mirror:Extended object

C

R> 0

Vy > 0

Object

Image

s > 0

y< 0


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Concave Mirror:Focal Point and Focal Length

where: f > 0: focal length

R > 0: radius of curvature


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Concave Mirror:Focal Point and Focal Length

where: f > 0: focal length

R > 0: radius of curvature


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Concave Mirror:Graphical Method


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Example:


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Seatwork:A mosquito landed 20 cm in front of a concave mirrorwith

20 cm radius of curvature. How far from the mirror will the

mosquitos image be formed?

A. 40 cm behind the mirror

B. 10 cm behind the mirror

C. 10 cm in front of the mirror

D. 20 cm in front of the mirror

E. At infinity


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Convex Mirror Concave Mirror


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Convex Mirror:Point object

CR< 0V

optic axis

Object P

Image P

s > 0

s< 0


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Physics 72 Bareza AY 15-16 1st sem s< 0

Convex Mirror:Extended object

C

R< 0

V

y > 0

Object

Image

s > 0

y > 0


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Convex Mirror:Focal Point and Focal Length

where: f < 0: focal length

R < 0: radius of curvature


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Convex Mirror:Focal Point and Focal Length

where: f < 0: focal length

R < 0: radius of curvature


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Convex Mirror:Graphical Method


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Example:


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Seatwork:You hold a large silver spoon a distance of 5.0 cm in front of

your face. The radius of curvature of the spoon is -20.0 cm.

What is the distance between the object and the image andthe nature (real or virtual) of the image?


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Refraction at a Spherical Surface34-3

OBJECTIVES

Given an object in front of a spherical surface or interfaceseparating two media:Calculate the location of the image



Calculate the apparent depth of an object when observedacross a boundary changing indices of refraction



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Image of a Point Object


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Image of an Extended Object


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Refracting surface:Object-Image Relationship and Magnification

valid for both concave and

convex refracting surface

Note:na : index of refraction of material 1nb : index of refraction of material 2


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Example:


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Seatwork:


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A special case:Plane refracting surface

Object-Image Relationship

Magnification

Radius of Curvature

na nbMaterial 1 Material 2

Plane refracting surface


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Example:


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Seatwork:


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Thin Lens34-4

OBJECTIVES

Differentiate a converging lens from a diverging lens

Given an object in front of a lens or series of lenses:Calculate the location of the image



Relate the radii of curvature of the lens in air and its index

of refraction of the focal length of the lens Given an object placed in front of a lens or series of lenses,

draw the principal rays and locate the image



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Thin Lens34-4


What is a lens?an optical system with two refracting surfaces

Thin lens two spherical surfaces close enough together negligible thickness

Converging Lens

Diverging Lens


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Thin Lens34-4


Converging Lens thicker at its center than at its edges


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Thin Lens34-4


Properties of a Converging Lens

f: focal length (f> 0)

F1 :1st focal point

F2 : 2nd focal point


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Thin Lens34-4


Converging Lens:Graphical Method and Principal Rays

s> 0s > 0

f > 0


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Thin Lens34-4


Converging Lenses:Object-image relationship and Magnification

where: f : focal length

s : object distance

s : image distance



f> 0 : converging lens


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Thin Lens34-4


Diverging Lens thicker at its edges than at its center


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Thin Lens34-4


Properties of a Diverging Lens

f: focal length (f< 0)

F1 :1st focal point

F2 : 2nd focal point


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Thin Lens34-4


Diverging Lens:Graphical Method and Principal Rays

s< 0

s > 0

f < 0


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Thin Lens34-4


Diverging Lenses:Object-image relationship and Magnification

where: f : focal length

s : object distance

s : image distance



f< 0 : diverging lens

3


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Thin Lens34-4


Example:

hi34 4


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Thin Lens34-4


Example:

hi34 4


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Thin Lens34-4


Example:

Thi L34 4


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Thin Lens34-4


Diverging lens: f< 0

|f | = 48 cm |f | = 48 cm

s = 16 cm

s = -12 cm

y y'

Thi L34 4


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Thin Lens34-4


Example:

Thi L34 4


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Thin Lens34-4


Example:

Thi L34 4


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Thin Lens34-4


Lensmakers equation

Thi L34 4


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Thin Lens34-4


Lensmakers equation

where: f : focal length n : index of refraction of thin lens

R1 : radius of curvature of 1st surface

R2 : radius of curvature of 2nd surface

Thi L34 4


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Thin Lens34-4



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Geometric Optics

End of Chapter 34

chapter 34 geometric optics

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