4.3 WAVES (characteristics)
WAVEFRONTS
surfaces through crests
normal to the direction of energy transfer
RAYS :
lines in the direction of energy transfer
normal to the wavefronts
have
INTENSITY, I :
directly proportional
square of the amplitude
energy of the wave
I ∝A²
which are
and
which are
and
also have
which is
to the
hence
because
directly proportional
square of the amplitude
is also
to the
I = Power/area
is defined as
Wm‾²
with unit
SUPERPOSITION 💥
happens when
2 or more waves of the same type
a given point in space at the same time
the displacement of the medium at that point
arrive at
hence
algebraic sum of individual displacements
is the
y=y₁ +y₂
a pulse created in a rope with one end fixed
a positive and negative pulse superpose
for example, when
cancel each other out
totally overlap
the rope looks flat
they
has the value
y₁ and y₂ are individual displacements
where
when they
it is moving
hence
but
when
a fixed end
a free end
approaches
Newton's 3rd Law
it experiences
a wall
for example
exerts an equal but opposite force on the rope
the pulse is reflected by the wall and inverted
the wall
hence
a phase change
180° when reflected
of
the pulse moving in the opposite direction
not inverted
no phase change
there is
is
⭐POLARIZATION ⭐
undergo
transverse waves
occurs only in
the electric field
2 types of oscillations is perpendicular
the direction of propagation
because
to
many modes
electric field
electromagnetic wave
for example
in an
happens when
electromagnetic wave
the same plane
in an
oscillates on the
passing it through a polariser
occurs by
vertical transmission axis
with a
in the path of unpolarised light
placed
transmit only vertically polarised light
hence it will
REFLECTION from a non-metallic surface
may be achieved by
the reflected ray is partially polarised
when this happens
the reflected light
various components
electric field of unequal magnitude
which means
has
of
partially horizontally polarised
or
'glare' from the reflections
wearing Polaroid sunglasses
vertical transmission axes
produce
can be reduced by
which have
MALUS'S LAW
how the intensity of polarised light
by a 2nd polariser (analyser)
tells
is affected
I = Iₒ cos²ϴ
is defined as
ϴ is the angle between the plane of polarisation
the transmission axis of the polariser
where
and
how much the intensity of transmitted light is reduced
determines
the 2nd polariser
by
Iₒ is the incident intensity
I is the intensity of light
