Physics of the 3D Illusion: Light as a Wave

Physics of the 3D Illusion:
Light as a Wave
Dr Lisa Jardine-Wright,
Cavendish Laboratory

What is a Wave?
• A wave is a disturbance which travels
from one place to another.
• As it travels, the wave transfers energy
from one place to another but NOT
material.

Describing Waves
• Wavelength, λ
o Distance before the wave repeats.
o Units are metres, m.
λ
o E.g distance between two peaks or troughs
of the wave.
λ
λ

Describing Waves
• Frequency, f
–The number of whole waves that pass a
fixed point each second.
–Unit is Hertz, Hz.
0.5 Hz

Describing Waves
• Amplitude, a
–Maximum displacement of the wave.

Describing Waves
• Speed of the wave, v
o Speed = frequency x wavelength
v=f x λ
• The speed of a wave is only altered by
changing the medium through which it
travels.
o Speed of sound in air = 340 m/s
o Speed of sound in water ≈ 1500 m/s

Types of Wave
• Transverse
Direction of the energy
transfer
• Longitudinal
Direction of the energy
transfer

Types of wave

Examples of Waves
• Sound
–Longitudinal
–Mechanical

Examples of Waves
• Ripples on a pond
–Transverse
–Mechanical

Examples of Waves
• Mechanical waves need a medium to
travel through.
• Light
o Transverse
o Electromagnetic
o Can travel through a vacuum – How!

Electromagnetic Spectrum: Light

Electromagnetic waves
• Visible light is a combination of electric
and magnetic field at right angles to
each other.
o The direction of the electric field is usually
used to describe the wave.

How or Why do we see in 3d?
• Two very slightly different
perspectives.
o Each eye views the world from slightly
different positions which gives the
illusion of depth.
o What happens if we can only use one eye?

Convincing the Brain
• A 2d image can appear 3d if we
convince the brain that each eye is
seeing something slightly different.
• Stereograms...

Using colour filters
• We can make the eyes see different
things if each eye can only see one
colour!

Colour filtering?
What does this
say when you look
through the red
filter and read?

3D & Colour
• What
direction is
the dog’s
nose pointing
when you
look through
the red
filter?

Using Polarisation
• Instead of using colour filters we can
polarise the light so that each eye sees
a slightly different image.
• What is polarisation?

Linear Polarisation
Wire grid polariser
Unpolarised light =
many different electric field directions

Linear Polarisation
• A Polaroid polarizing filter is rather
similar to the wire-grid polarizer.

Linear Polarisation by Reflection
• Non-metallic surfaces such as asphalt
roadways, snowfields and water reflect
light such
that it is
polarised
parallel to
the reflecting
surface.

Polarisation in Use

Polarisation in Use

Linear Polarisation by Refraction
• When light
refracts it
will also be
polarised.
• Light can be
polarised by
crystals

Circular Polarisation
Light travels faster in this direction

Circular Polarisation

Circular polarisation example

Circular Polarisation & 3D
Right Handed
Left Handed

Light & Lasers
• Light Amplification
by stimulation of
emission radiation
• Lasers are useful
because their light
is monochromatic &
coherent

Coherent waves
• Coherent waves are
waves that are in
phase with each other.
• Ordinary light is not
coherent because it
comes from
independent atoms
which emit on time scales of about 10 -8
seconds.

How do lasers work?

How do lasers work?
hyperphysics.phy-astr.gsu.edu

3D in Action: Where to go first!
30 th March 31 st March
A
(lecture
theatre)
B
(Labs)
• Ely College
• Stephen Perse
• Impington
• Stowmarket
• Great Cornard
• Hartismere
• Wymondham
• Abbey College

2 pm
Programme
Group A
Experimenting
with vision & 3D
(Workshop)
Group B
Uses of Light in
BioPhysics
(Talks)
2:45 pm Break
3 pm Break
Experimenting
3:15 pm Uses of Light in
with vision & 3D
BioPhysics
(Workshop)
(Talks)
4pm
THE END