New Light Express Presentation

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LIGHT
fantastic
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Beam Show
Beam Show
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University of Southampton
School of Physics and Astronomy
Light at the forefront of Physics

• Light as a wave
• Relativity
• Quantum mechanics
• Particle physics

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Light is a Wave
? (wavelength)
Evidence
Double slit experiment
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Double Slit Demo
Double Slit Demo
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Interference

• Constructive (bright points of light)

Destructive (dark areas)


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The Diffraction Grating
colour sorter
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Candle Light
Candle light
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Laser light is coherent, monochromatic and
non-dispersive
Light Amplification by Stimulated Emission
of Radiation
Fluorescent Dye emits a broad spread of
wavelengths
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Add Dye
Add Dye
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The Speed of Light
For water waves the motion of an observer will
change the speed of the waves
c

c v

v
We should be able to see this effect using the
motion of the Earth
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Michelson and Morley
In 1887 Michelson and Morley did an experiment to
detect the ether using the Earths motion
relative to the ether
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Interferometer Demo
Interferometer Demo
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The experiment failed to detect any time
difference for the two paths!
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Relativity
Light is an electromagnetic wave there is no
ether
The speed of light is the same for any observer!
This means nothing can travel with light
nothing can reach vc!
Rest mass energy
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Space - Time
A flash of light causes a spherical wave front
even if you move relative to source
This only makes sense if space and time mix!

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Light and Matter
Photo-Electric Effect
Light can provide energy to kick electrons out of
a metal
Light
e-
Metal
If light intensity is lowered so there is less
energy, we expect the evicted electrons to have
less energy but they dont we just see fewer
electrons of the same energy
The energy in light comes in lumps!
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The size of the energy lumps depends on frequency
Light
e-
Metal
If we reduce the frequency too much then the
electrons dont receive enough energy to escape
the metal surface
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PE Demo
PE Demo
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Light Quanta
The energy in light comes in lumps
In a sense we can think of light as particles in
our detector - photons
Quantum Mechanics is the theory of the dynamics
of these quanta
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Diracs Legacy
Electrons can absorb photons
e-
time
But in relativity observers do not agree on time
ordering of events so can we have
e-
time
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What does it mean for an electron to travel
backwards in time? We only measure charge
-q

q
time
It looks like a ve charge electron moving
forward in time
We have discovered anti-particles!
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Particle Physics
e-
energy in
New Particles
photon
e
time
Electron positron annihilation to a photon allows
us to convert their energy to look for all the
particles that make up nature
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At the LHC collider, currently being built, we
will produce 100 billion collisions per second!
How can we communicate so much data?
In 1990 Tim Berners-Lee invented the Web to
transfer our data!
And laser light now carries the information
around the world
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Fibre Optic
Fibre Optic
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the Light fantasticwas brought to you by

• Nick Evans
• Pearl John
• James Gates
• Keith Wilcox
• Matt Praeger
• Sunil Patel

www.lightexpress.soton.ac.uk
Thank You
For more information, please contact Pearl John
The Light Express Coordinator pj_at_soton.ac.uk
023 8059 2159