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MK FISIKA DASAR 2ENGE600004
4 SKS
Rachmat Andika
Multiferroic Research Group
Departemen FisikaFMIPA - UI
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THE NATURE OF LIGHT AND
THE LAWS OF
GEOMETRIC OPTICS
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MATERI
The Nature of Light
Dualism of Light
The Speed of Light
Reflection and Refraction Total Internal Reflection
Dispersion
Huygens’s Principle
Fermat’s Principle
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THE NATURE OF LIGHT
The light can propagate in a vacuum media
The light has a wave properties, such as Reflection
Refraction
In seeing something, the light has an important role
for our eyes
A rainbow is one of the product of light that dispersed
by rain/ water
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HISTORICAL OF LIGHT
Newton Light was considered to be a stream of particles that was emitted by
the object
He could explain reflection and refraction
Huygens (1678) Wave theory could also explain reflection and refraction
Young (1801) Light rays interfere with each other and it couldn’t be explained by a
particle theory
Maxwell Light was a form of high-frequency electromagnetic waves
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BUT ….
They could not explain some subsequent experiments,
such as
Where the constant of proportionality h = 6.63 x 10-34 Js
Photoelectric Effect
Max Planck (1900) → Einstein (1905)
The quantization model assumes that the energy of a
light wave is present in particles called photons
Is light a wave or
particle?
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THE RAY APPROXIMATION IN
GEOMETRIC OPTICS
In the ray approximation, we assume that a wave moving through a
medium travels in a straight line in the direction of its rays
λ >> d, the rays continue in a straight-line path, and the ray
approximation remains valid
λ ≈ d, the rays spread out after passing through the opening λ << d, the opening behaves as a point source emitting spherical
waves
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WAVE FRONT
To simplify light as a wave
Wave front is every point on wave crest
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REFLECTION
The direction of a reflected ray is in the plane
perpendicular to the reflecting surface that contains the
incident ray
Specular reflection on a
smooth surface
diffuse reflection on a
rough surface
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LAW OF REFLECTION
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THE DIFFERENT BETWEEN
REFLECTIONS
For diffuse reflection, the eyes could see the light
reflection on all angles
For specular reflection, the eyes should have to
on the right position with respect to the light
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EXAMPLE
Two mirrors make an angle of 120o with each other. A
ray is incident on mirror M1 at an angle 65o to the
normal. Find the direction of the ray after it is
reflected from mirror M2?
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REFRACTION
When a ray of light traveling through a transparent
medium encounters a boundary leading into another
transparent medium,part of energy isreflected andpart
enters the second medium
The ray that enters the secondmedium is bent at the boundary
A basic definition of refracted
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(a) The light is bent toward the normal
(b)
The light is bent away from the normal
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INDEX OF REFRACTION
In general, the speed of light in any material is less than its
speed in vacuum.
In fact, light travels at its maximum speed in vacuum.
Index of refraction is a dimensionless number greater than unity Becausev is always less thanc.
n is equal to unity for vacuum
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SNELL’S LAW OF REFRACTION
As light travels from one medium to
another, its frequency does not change
but its wavelength
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EXAMPLE
A beam of light of wavelength 550 nm traveling in air
is incident on a slab of transparent material. The
incident beam makes an angle of 40.0o with the
normal, and the refracted beam makes an angle of
26.0o
with the normal. Find the index of refraction of the material
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EXAMPLE
A light ray of wavelength 589 nm traveling through
air is incident on a smooth, flat slab of crown glass at
an angle of 30.0o to the normal Find the angle of refraction
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EXAMPLE
A laser in a compact disc player generates light that
has a wavelength of 780 nm in air. Find the speed of this light once it enters the plastic of a
compact disc (n = 1.55)
What is the wavelength of this light in the plastic
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Angle of deviation
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HUYGEN’S
PRINCIPLE
All points on a given wave front are taken as point sources for theproduction of spherical secondary waves, calledwavelets, which
propagate outward through a medium with speeds characteristics of
waves in that medium.
After some time interval has passed, the new position of the wave front
is the surface tangent to the wavelets
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DISPERSION AND PRISMS
Index of refraction varies with the wavelength of the light passing
through the material. “ Dispersion”
Snell’s law of refraction indicates that light of different wavelength isbent atdifferent angles when incident on a refracting material.
Angle of deviation is an angle between a ray of single wavelength
incident on the prism from the left emerges refracted from its original
direction of travel
Angle of
deviation
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Visible spectrum
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MEASURING INDEX OF
REFRACTION USING A PRISM
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TOTAL INTERNAL REFLECTION
Total internal reflection can occur when light is
directed from a medium having a given index of
refraction toward one having alower index of
refraction
θc : critical angle
The refracted light ray
moves parallel to the
boundary, θ2 = 90o
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EXAMPLE
Find the critical angle for an air-water boundary
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FERMAT’S PRINCIPLE
Fermat’s principle states that when a light ray travels
between any two points, its path is the one that requiresthe smallest time interval
PIERRE DE FERMAT(1601-1665)
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IMAGE FORMATION
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MATERI
Images formed by flat mirrors
Images formed by spherical mirrors
Images formed by refraction
Thin LensesLens Aberrations
Optics Systems
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IMAGES FORMED BY FLAT MIRRORS
Images are classified as areal orvirtual
A real image is formed when light rays pass through and diverge from
the image point
A virtual image is formed when the light rays do not pass through theimage point but only appear to diverge from that point
the image of an object seen in a
flat mirror isalways virtual
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The image is as far behind the mirror as the object isin front
The image is unmagnified, virtual, and upright
The image has front-back reversal
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IMAGES FORMED BY SPHERICAL
MIRRORS
Concave mirror Mirror, in which light is reflected from the inner, concave
surface
Concave mirror is sometimes called aconverging mirror,
because the rays from any point on an object converge after
reflection
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IMAGES FORMED BY SPHERICAL
MIRRORS
Convex mirror Mirror, in which light is reflected from the outer, convex
surface
Convex mirror is sometimes called adiverging mirror,
because the rays from any point on an object diverge after
reflection
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MIRROR EQUATION
fis focal length,
fis usually not the point at which the light rays focus to form an image.the focal point is determined by the curvature of the mirror
It doesn’t depend on the location of the object at all
Or doesn’t depend on the material of mirror
But it is different for lenses
The light actually passes through the
material and the focal length depends on the
type of material of the lens
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RAY DIAGRAMS FOR MIRRORS
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RAY DIAGRAM OF CONCAVE
MIRRORS
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RAY DIAGRAM OF CONVEX MIRRORS
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THIN LENSES
Lens makers’ equation
Lenses are used to form images by refraction
in optical instruments, such as cameras,
telescopes, and microscopes
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RAY DIAGRAM FOR THIN LENSES
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EXERCISE
Two thin converging lenses of focal lengths f1 = 10 cm
and f2 = 20 cm are separated by 20 cm. an object is
placed 30 cm to the left of lens 1. Find the position
and the magnification of the final image.
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