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Transcript
LIGHT: Geometric Optics
The Ray Model of Light
• Light travels in
straight lines under a
wide variety of
circumstances
• Light travels in
straight line paths
called RAYS
Optical Instruments: Refractive
Thin Lenses
CONVEX
Converging Instrument
thicker in the middle
CONCAVE
Diverging Instrument
thinner in the middle
CONVERGING LENS
• Causes parallel rays to converge
• Produces real and virtual images.
• Focal Length is positive.
Ray Tracing for Converging Lens
Ray 1: Parallel emerge through F
Ray 2: Through F emerge Parallel
Ray 3: Straight through center
The Lens Equation
• 1/do + 1/di = 1/f
• m = hi/ho = - di/do
– m is magnification
• ho/hi = do/di
DIVERGING LENS
• Causes parallel rays to diverge
• Produces only small-virtual images.
• Focal Length is negative.
Ray Tracing for Diverging Lens
• Focal length is
negative for any
diverging instrument.
• Image distance is
negative for virtual
images.
• Virtual image
produced will be
smaller than object.
Angular Magnification
Who invented the telescope?
Refracting Telescope
Compound Microscope
The eyepiece is placed such that the image
formed by the objective falls at first focal point
of the eyepiece. The light thus emerges as
parallel rays.
Can you explain this?
Total Internal Reflection
• Red light is incident on the glass-air boundary at
an angle greater than the critical angle.
– although red, when compared to blue and yellow, has
the lower index of refraction.
Can you explain this?
• The pattern formed is
from a converging
lens.
Spherical Aberation
Chromatic Aberration
• Each color has a
different focal point.
• The refractive index is
different for each
wavelength.
Reflection
• Law of Reflection
– The angle of incidence
equals the angle of
reflection
• The incident and
reflected rays lie in the
same plane with the
normal to the surface
Diffuse vs Specular
Reflection
• Diffuse Reflection
– Light incident upon a
rough surface
– Law of reflection still
holds; Normals not ll.
• Specular Reflection
– Mirror like reflection
– All Normals are
parallel
Image formation by a Plane
Mirror
• Image distance equals
the object distance.
• Image size equals the
object size.
• Virtual image formed.
Optical Instruments: Reflective
SPHERICAL MIRRORS
CONVEX
Diverging Instrument
CONCAVE
Converging Instrument
CONVEX MIRROR
• Produces only smallvirtual images.
• Focal Length and
Radius are negative.
• Anti-Theft, RearView, Safety
CONCAVE MIRROR
Real image formed by
Converging Rays
Virtual image formed by
Diverging Rays
• Produces both Real and Virtual Images
– Real images can be magnified or reduced
– Virtual images are always magnified.
CONCAVE MIRROR
•
Real
Virtual
– Real images can be magnified or reduced
– Virtual images are always magnified.
Equations to Apply
• f = r/2
– f is focal length
– r is radius
• ho/hi = do/di
–
–
–
–
h is height
d is distance
o is object
i is image
• 1/do + 1/di = 1/f
• m = hi/ho = - di/do
– m is magnification