Light Unit
537
470
Properties of waves
light
Waves a moving disturbance that transports energy from one
place to another
wave crest upperpart of a wave
atam n
wavelengh X
Cravefront
Phases
offset
of
a
wave
A
The speed of
from a
wave trough
shifted
in reference to
Red
a periodic wave
Point
recreate
Blue wave is
is related to
bygeparta
I
wave
its wavelength
and frequency
Ve ft
Reflections
a change in
direction of
a
light ray
when it
meets an obstacle where the incoming e outgoing
I
AM
e
rat
a
kit
i
I
Norma
is
mirrors are an
example of reflect
where incidentangle
reflection angle
have the
mirrors
same angle of incidence
refrtection
because
For reflection from a flat surface angle
always equals theangle of reflection
Specular reflection 8 reflection
on a
of incidence
flat surface where all
reflecting rays are in the same direction
Diffuse reflectiona reflection on
Ink
a
rough surface where reflected
w
Refraction 8
the bending of light as it travels at
one medium to
an angle
from
another
incidentraggy reflection ray
reararea
ray
II Is
Principle of reversibility
reversed
air
y
light ray will follow the same
path if it's direction of travel is
a
J
n
i
water
t
i
reverse
I
II
T
ndex of
The
refraction
n
of the speed of light
one medium to another
a ratio
in
higher the index of retraction
air
water
The lower
the speed of
light
13
a magnifying
1087
at
speed of
Example of refractions
2.5
glass has
a
light b
lens that bulges
outwards As Light hits the glass at an
angle
it gets retracted towards the
centre of the lens
allowing us to see
objects bigger
Dispersion Speed of the wave depends on it's
as proven by the formula Vefa
frequency travelers
however when a wave enters a new medium frequency
Basedonfreaanly
lightslowsdown
ndispersivemediums
doesnot change but wavelengh does this happens
because frequency is characteristics of thesource of light
this dependance
of the speedof light on wavelengh causes
light waves to separate in
Dispersion in
real
life 8 Diamonds
a phenomenon
are an example
called dispersion
of dispersion as
dispersion occurs when light passes thru a diamond
thedifferent wavelengthsbend slightly at differentangles
causingthem to spreadout
light
diamond
form a spectrumofcolors
dispersions color
Critical angles smallest angle
of incidence from which a light ray
d
d
ie smallest angle possible
g
tiffin
no retracted ray and inciden
If find
0
Sin
h
for
ray is reflected atthe
I
Total internal
Sino
reflection
devices can be usedto
change direction of a
light beam
Diffraction8 thebending spreading of a wave when it
Passes thru an opening
waves spread out when Passingthrough an obstacle
B
Ig
g
d
a
A
Assizeof slit b diffraction T
Interferences when 2 waves
in the same medium interact
Constructive Interference
Destructive interference
displacement in the same direction
Waves are in phase so they
wave 2
Coherent
waves
are
oppositedirection
188 apart
cancel
iii
iii
amplicy
Wave I
displacement in
waved
N
A
waves having the same frequency
Interference in real
life
noise
cancelling headphones
Inceleachother
fixed waves
use destructiveinterferen
to cancel unwantedsound bycreating
an opposing
soundwave that mimics the noise you want to se
nodallines destructive
g
rid of but just 1800 out of Phase
noaal lines T when frequency t
when wavelength d
noda lines t
n
Light is classified both
Particle As
as
Newton
a
particle
wave
wave
M
Huygens
V
election
etraction
terferenie
efraition
É
X
X
olarization
Young's Double
Slit experiment
Interference fringes one of a series of alternating lighta dark
fringes that result from the interference of waves
by Bg Bg
Bbq
4
Display of young'sexperiment
Interference in thin films
Thinfilm's
a
Transmition
very thin layer of a substance on a supporting material
eg thinfilms of oil on road
a
wave
reflect
Inversion
lengh that goes through a medium does not
so it's not inverted
light waves being shifted by half
So it it was
it's now
when does inversion happen when a
fixed end
M
GI
Itis
Gif
u
n
wave
a wave lengh
n
reflects from
or encounters a
decreases a medium
w a
wave
higher indexof
refraction
Tresults indestructiveinterference
because crestand trophcancel out
Air Wedges the air between 2 sheets of
a
medium
in which the speed of the
I
E
flatglass angled toform a
wedge
light reflects transmits interfere with surfacesthat
have differentseparations at diff locations
i
first
aimed
inversion
Destructive
A
t
Thicke
ya
inversionhappens
herebecause nglasshair
Sothiswaveis shiftedbyIz
Single slit diffraction
Central maxima8 Bright central region in interference that is
2x the normal brightness of maxima
Polarization of
Polarized light
light
lightwaves thatvibrate in a
single plane
Unpolarizedlight light waves that vibrate in many different planes
Polarizer devicethatallowsonly
light with anelectricfield along a
singledirection to passthrough
transmission axis'sdirection of
a
field that
a polarizerallows
thru
axis of Polarization vertical
onpolarized
i
light
Folarizen
i
rn
7
verticalpolarized
transmission
light
axis
Selective obsorbtion s unpolarized light polarized when
passed thru a polarizer thetransmition axis
determines direction
of Selective absorption
generate developed filmimages They are made up of molecules that
selectively absorblight who's electric field is alongthe direction of
the molecule
transmits lightwhen electric field is parallel to transmition axis
Polariods are example
Polarization by reflection 3 a wavelength is partially polarizedwhe
it reelects
EEE
unharmed
light
1175 Id
polarization occurs whenthe
angle between transmitted a reelected
too
is
an
NiSind
n z sin
z
Sinlao 0
ni sing h2
nisino nz coss
Polarization by scattering
Tano
Scattering change in directionof light waves as a result of collision
with otherparticles such as oxygen nitrogen
LCD and optical activity's
optical activity rotation of the direction
Liquid crystal display
y
LCD
of
polarization
thin flat display
that makes use of polarizes
a optical activity
a
LCD
kno current LCD works
current LCDdoes notwork
Why sky is blue during the day a red duringsunset
Sun has many
color rays such as Blue violet red
won
Xp
s
Bluewaveshaveshorter
mien
scatter
shorter wavelengths
Red has longerwavelengths
more meaning Blue scatters more
As 29 scattering
As Ab scatteringA
day
Duringthe
sun is aboveEarth
Sunset sunrise
Doring
not above Earth
Sun
is
distance
Earth
an
Meaningthatthereis lessdistance
for the
Meaningthere is more distance for
the light to travel
lighttotravel
meaning that less scatteringoccurs as molecules morescatteringoccurs as molecules aregiven
donothave enoughtimetocollidewiththerays
Therefore we seeblue
as eventho theblue
rays get scattered more than other rays there
s not enoughtime for them
to scatter out of
more time
tocollide withthe rays
Because Red has the biggestwavelengh
it get's scattered the least anddoes no
leavetheatmosphere which is why we scene
the Earth'satmosphere thereforethey scatter whileblue gets scattered so much most
in
o
Earths atmosphere and is the reason it leavesEarth'satmosphere
why we see a blue
the universe
sky
escapes to