Light Properties Lecture
Transcript of Light Properties Lecture
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Properties of lightProperties of light
1. Speed of light is c =2.9979 x 108 m s-1.
c is an absolute constant and nothing
travels faster than c.2. Light has two characteristics. It is a
wave and it can act as particles. This
is known as duality nature of light.3. It is an electromagnetic wave which is
visible to our eyes as 7 colours.
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Properties of lightProperties of light
4. Since it is a wave, the followingcharacteristics of light are observed:
(a) Reflection
(b) Refraction(c) Diffraction
(d) Interference
(e) Polarization5. Light as a wave has the relationship:
c = f where f is frequency,
is wavelength
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Properties of lightProperties of light
5. When light acts as particles, theyare energy particles known asphotons.
6. The energy of photons:
E = nhf
where n is no. of photonsh is Planck constant
f is frequency of light
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LASER
LASER
Light travels in a straight line
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Shadows
Shadows are places where light is blocked:
Rays of light
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Light travels much faster than sound.For examples:
1) Thunder and lightningstart at the same time,but we will see the
lightning first.
2) When a starting pistolis fired we see theflare first and thenhear the bang.
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Light is a visible electromagneticLight is a visible electromagneticwavewaveElectromagnetic SpectrumElectromagnetic Spectrum
Increasing Wavelength
Visible Light
400nm 500nm 600nm 700nm
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Reflection of LightReflection of Light
Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle ofincidence
Angle ofreflection
Mirror
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The Law of ReflectionThe Law of Reflection
Angleof incidence= Angleof reflectionAngleofincidence= Angleofreflection
Thesame !!!
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We see things because they
reflect light into our eyes:
KKBI
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Luminous and non-luminous objects
A luminous object is one that produces light.
A non-luminous object is one that reflects light.
Luminous objects Reflectors
The sun The moon
Lamps Mirrors
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Clear vs. Diffuse ReflectionClear vs. Diffuse Reflection
Smooth, shiny surfaceshave a clear reflection:
Rough, dullsurfaces havea diffuse reflection.
Diffuse reflection is whenlight is scattered indifferent directions
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Using mirrorsUsing mirrors
Two examples:
1) A periscope
2) A car headlight
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Refraction of Light
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Laws of refractionLaws of refraction
i
r
i
rglass
Vaccum/air1. The incidence ray,
refraction ray andthe normal all lie inthe same plane;
2. nconstant,r
i!
sin
sin
Normal
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Whitelight
Prism
Red
OrangeYellow
Green
Blue
Indigo
Violet
The colours of the rainbow:The colours of the rainbow:
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i
rred
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Wavelengths of coloursWavelengths of colours
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DiffractionDiffraction
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Diffraction of lightDiffraction of light
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a Diffraction pattern of light
Diffraction of lightDiffraction of light
Around a razor bladeAround a razor blade
At a slitAt a slit
Around a circular discAround a circular disc
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Interference of lightInterference of light
lampS1
S2
waves fromS1
waves fromS2
fringesinterference occurswhere beams cross
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Polarization of LightPolarization of Light
Polarization is the separation ofPolarization is the separation ofa beam of light so that thea beam of light so that the
vibrations are in one plane.vibrations are in one plane.It is an exclusive property ofIt is an exclusive property oftransverse waves.transverse waves.
When a light wave is produced, itWhen a light wave is produced, itvibrates in many directions.vibrates in many directions.
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Polarization of LightPolarization of Light
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Photoelectric effectPhotoelectric effect
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Photoelectric effectPhotoelectric effect
Emax
ffo0
-W Emax = hf - W
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Emax = hf W
W is the work function, i.e. theenergy required to release theelectrons;
But Emax = eV ,Then eV = hf W,
When eV = 0, W = hfo eV = hf hfo
eV = h (f fo)
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LensesLenses
f
F
Focal plane
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Angular magnification, MAngular magnification, M
ao
D
ho
D
ha
object,anbyretinatheonsubtendedAngle
oo !
vision)eye(normalcm25Dwhere !
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Angular magnification, MAngular magnification, M
ho a1
u
f
f
u
ha 01 !
u
DM
h
D
u
h
a
aMion,magnificatAngular
0
0
0
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!@
v!
!@
Magnification of image at
infinity
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M when u = fM when u = f
f
DM !
ho a1 ff
Magnification of image at infinity
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TelescopeTelescope
Eye
lens
Virtual
image
Fe
Fe
Fo focal point ofobject lens
Fe focal point ofeye lens
Fo
Object lens
Realimage
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Magnification of Telescope at NormalMagnification of Telescope at NormalAdjustmentAdjustment
Imageformed at
infinity
Fe
Fe
Fo
fo fe
h a1ao
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f
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hf
fh
a
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v!
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Length of telescope is (fo+fe)
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MicroscopeMicroscope
Virtual
image
Object
Object lens
Eye
lens
FeFo
FeFoRealimage
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Magnification of a microscopeMagnification of a microscope
FeFo
FeFo
ho
h
h1
a1
e0 mmM v!
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D
ha,icroscopeusingretinatheatsubtendedAngle
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11
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e andmo arethe
linearmagnificationofeyelens andobject
lensrespectively
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Opera telescopeOpera telescope
How does the image form in
the opera telescope?
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