Transcript Thin Lenses - sdeleonadvancedphysics

Thin Lenses
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lowest grade.
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Lecture fom Mirror
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From what material are curve mirrors
made from?
How plane and curve mirrors formed
images?
What are the types of curved mirrors?
State the mirror and magnification
equation use to locate an image in
curved mirrors.
What is prism?
Light going through a prism
bends toward the base
n1
n1 =1
n2
n1
Bending angle depends on value of n 2
Refraction in Prisms
If we apply the laws of refraction to
two prisms, the rays bend toward the
base, converging light.
Parallel rays, however, do not converge
to a focus leaving images distorted and
unclear.
Two prisms base to
base
Refraction in Prisms
(Cont.)
Similarly, inverted prisms cause parallel
light rays to bend toward the base
(away from the center).
Again there is no clear virtual focus,
and once again, images are distorted
and unclear.
Two prisms apex to
apex
Lenses?
What is a lens?
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A transparent object that refracts light
rays, causing them to converge or
diverge to create an image
Types of Converging
Lenses
In order for a lens to converge light it must be thicker near the midpoint to
allow more bending.
Double-convex
lens
Plano-convex lens
Converging meniscus
lens
Types of Diverging
Lenses
In order for a lens to diverge light it must be thinner near the midpoint to
allow more bending.
Double-concave
lens
Plano-concave lens
diverging meniscus
lens
Converging Lenses
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A converging lens is thicker at the
middle than it is at the rim
– The front of the lens is the side of the
lens where the object is
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Converging lenses can produce real or
virtual images
Converging Lenses
2F
F
F
2F
The focal points are equidistant from the center of the lens. That distance
is the focal length of the lens.
Converging Lens
Reference Rays
Ray
From object to From lens to
lens
image
Parallel Ray
Parallel to
principal axis
Passes through
focal point F
Central Ray
To the center of
the lens
From the center
of the lens
Focal ray
Passes through
focal point F
Parallel to
principal axis
Converging Lenses
Ray 1
2F
F
F
2F
The focal points are equidistant from the center of the lens. That distance
is the focal length of the lens.
Images Created by Converging Lenses
Images produced by lenses
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An object
infinitely far away
from a converging
lens will create a
point image at
the focal point
– i.e. light from the
Sun
Images produced by lenses
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As a distant object
approaches the focal
point, the image
becomes larger and
farther away
Images produced by lenses
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When the object
is at the focal
point, the light
rays exit parallel
to each other
and the image is
“at infinity”
– i.e. a lighthouse
or a searchlight
Images produced by lenses
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When the object is inside the focal
point, the rays are drawn the same
way but you must extend them
backwards in order to find the image
Converging Lens: Objects inside the
focal point
Draw lines extending
backwards to form
the image
2F
F
F
These rays
are diverging
and won’t
cross
2F
Summary
Object
position
Image
Position
Real or
virtual
Magnified
or
diminished
Inverted or
erect
>2F
between F
and 2F
real
diminished
inverted
at 2F
at 2F
real
same size
inverted
between 2F
and F
> 2F
real
magnified
inverted
at F
at infinity
between F
and lens
same side
as object
virtual
magnified
upright
Locate and describe the image below
Diverging
Converging
2.
Seatwork 1 (Lecture
Note)
1.
2.
3.
A converging lens has a focal length of 17 cm. A
candle is located 48 cm from the lens. What type
of image will be formed, and where will it be
located?
A plano-convex lens of focal length 5.0 cm is used
in reading lamp to focus light from a bulb on a
book. If the lens is 60.0 cm from the book, how
far should it be from bulb’s filaments?
A toy of height 8.4 cm is balanced in front of a
converging lens. An inverted, real image of height
23 cm is noticed on the other side of the lens.
What is the magnification of the lens?
• The focal length of particular lens depends both on the index
of refraction n of its material relative to that of the medium it
is in and on the radii of curvature R1 and R2 .
1/f = (n-1) ( 1/R1 + 1/R2)
•
•
•
•
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R is + if the surface is convex.
R is – if the surface is concave.
f is + for converging lens
f is negative for diverging lens
It does not matter which surface is considered as1 and 2.
27
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A meniscus lens has a convex surface
whoe radius of curvature is 25 cm and
a concave surface whose radius of
curvature is 15 cm. The index of
rafraction is 1.52. Find the focal length
of the lens and wether it is converging
or diverging.
Thin Lens and Magnification
Equations
1 1 1
 
p q f
q
M 
p
Sign conventions for
lenses
+
p
Object distance for
lenses
q
Image in back of the
lens ( real)
Image in front of
the lens (virtual)
f
Converging Lens
Diverging Lens
Sample Problem
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Sherlock Holmes examines a clue by
holding his magnifying glass (with a
focal length of 15.0 cm) 10.cm away
from an object. Find the image
distance and the magnification.
Describe the image he observes. Draw
a ray diagram to confirm your
answers.
What kind of lens is a
magnifying glass?
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Magnifying glasses produce enlarged
images. Therefore, a magnifying glass
is a converging lens.
f = + 15 cm, p= +10 cm
Solve the problem
1 1 1 1 1
1
    
q f p 15 10
30
q  30 cm
q
 30cm
M  
 3
p
10cm
The image is virtual and upright
Magnifying Lens Ray Diagram
2F
F
Object
F
2F
Notice that the image is located at 2F (30 cm) and
it is also in front of the lens which is why q is
negative.
Diverging Lenses
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A diverging lens is thinner at the
middle than it is at the rim
A diverging lens has two focal points
but only one focal length
Diverging lenses only produce virtual
images
Diverging Lenses
2F
F
F
2F
The focal points are equidistant from the center of the lens. That distance
is the focal length of the lens.
Diverging Lens Reference Rays
Ray
From object to From lens to
lens
image
Parallel Ray
Parallel to
principal axis
Directed away
from focal point
F
Central Ray
To the center of
the lens
From the center
of the lens
Focal ray
Proceeding
toward back
focal point, F
Parallel to
principal axis
Drawing the Rays
Ray 1
2F
F
F
2F
Sample Problem (p.579 #1)
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Using a ray diagram, find the position
and height of an image produced by a
viewfinder in a camera with a focal
length of 5.0 cm if the object is 1.0 cm
tall and 10.0 cm in front of the lens. A
camera viewfinder is a diverging lens.
Ray Diagram
Object
2F
F
F
2F
The image is about 1/3 of the object height (.33 cm). The
image location is about 3 or 4 cm from the lens. So, q is
approximately -3.5 cm.
Smart people verify!
1 1 1
1 1
3
    
q f p
5 10
10
q  3.3cm
hi
q
M

ho
p
ho (q) 1cm(3.33cm)
hi 

 .33cm
p
10cm
Group 1 Human Eyes
a. Identify and describe the parts of the human eye
vital in seeing objects.
b. Describe how image is formed in the retina ( Ray
diagram is needed).
c. Explain how the eye accommodates to see
clearly both far and near objects.
Group 2 Camera
a. Identify and describe the parts of the camera.
b. Describe how image is formed in the camera
(Ray diagram is needed)
c. Similarities and differences of the camera and
the human eye.
Group 3 Vision Defects
a. Myopia and its Causes and corrective lens
(w/ ray diagrams)
b. Hyperopia eyes and its Causes and corrective
lens (w/ ray diagrams)
c. Presbyopia eyes and its Causes and
corrective lens (w/ ray diagrams)
d. Astigmatism eyes its causes and corrective
lens (w/ ray diagrams)
Group 4 Microscope
a. Parts of the microscope and its
function.
b. Image formation in objective and
eyepiece lens w/ ray diagrams
Group 5 Telescope
a. Parts of the telescope and its
function.
b. Image formation in objective and
eyepiece lens w/ ray diagrams
Group 6 Different Optical
Instrument
Picture and its uses / function/s
a. Periscope
b. Endoscope
c. Interferometer
d. Spectrometer
e. Sunglasses