What Is Light?
Light
Sunlight- energy
that makes life
possible on Earth
 Nuclear reactions
in the sun produce
a lot of energyone form is light
 Earth captures
only a small
amount of the
light, however it is
enough to heat
the Earth and
allow
photosynthesis to
occur

Properties of Light
 Travels
at a high speed – so fast it
can go around the Earth about 7.5
times in one second!
𝑐
A
= 3 × 108 𝑚/𝑠
packet of light energy is called a
PHOTON
 Light travels in a straight line
Light – An Electromagnetic Wave
What is a wave?

A wave is a disturbance that
transfers energy from one point to
another without transferring
matter.
Light is…
a particle AND a wave
Most waves need a medium…
 Medium
– any physical substance
(air, water, dust) that acts as a
carrier for the transmission of
energy.
 Sound
travels through air particles
 Water waves travel through water
 A rope or slinky can be a medium
for waves
How does light travel through
space?
Electromagnetic Waves
 The
term electromagnetic
waves is used to describe light
because light is made up of
oscillating electric and
magnetic fields.
Colours-electromagnetic waves
that the human eye can detect

What distinguishes colours of light is the
different wavelengths of light.
COLOUR SPECTRUM

These colours are called a SPECTRUM

White light is made up of shades of Red, Orange,
Yellow, Green, Blue, Indigo and Violet

ROY G BIV is a mnemonic to help you remember
the spectrum.
We can only sense so much…

When a dog whistle is blown, can
you hear it?

Some sounds are at such a high
frequency, we can’t hear them.

Our eyes can’t “see” some of the
electromagnetic spectrum
An example

When you use a microwave, you can’t see
the waves your food is absorbing.

The waves used to heat your food is
called Microwave radiation.
ELECTROMAGNETIC
SPECTRUM

Visible light spectrum is a very small
portion of a much larger spectrum called
the Electromagnetic Spectrum

Sample Mnemonic:
Rick’s Mother Is Visiting Uncle Xavier’s Garden
Visible light provides only limited
information about the universeThe Andromeda galaxy looks different
using different parts of the EM spectrum
How is light produced?
Light
production


Luminousproduces its own
light ex: the Sun
Non-luminous –
does not
produce its own
light, can only
be seen using
reflected light
ex: book, tree,
moon
WAYS TO GAIN
ENERGY &
PRODUCE LIGHT
 Incandescence
–
production of
light as a result
of high
temperature (ex.
Burning candle)
 Only 5-10% of
electricity is
converted into
visible lightinefficient
WAYS TO GAIN ENERGY &
PRODUCE LIGHT
 Electric Discharge – process of producing light by passing an electric
current through a gas (ex. Neon lights or lightning)
WAYS TO GAIN ENERGY &
PRODUCE LIGHT
 Materials are coated with phosphors –material that gives off light
 Phosphorescence – process of producing light by the absorption of UV
light resulting in the emission of visible light over an extended period of
time (ex. Glow in the Dark)
WAYS TO GAIN ENERGY &
PRODUCE LIGHT
 Fluorescence – immediate emission of visible light as a result of the
absorption of UV light (ex. Energy saving light bulbs)
 These bulbs are more energy efficient than incandescent bulbs however
they contain mercury so need to be treated like hazardous waste
 Detergents have fluorescent dyes that absorb UV light and emit visible light
 Highlighters use the same principle
WAYS TO GAIN ENERGY &
PRODUCE LIGHT
 Chemiluminescence (“cold-light”)– direct production of light as the result
of a chemical reaction with little or no heat produced (ex. Glow sticks)
Glowstick experiment
WAYS TO GAIN ENERGY &
PRODUCE LIGHT
 Bioluminescence – production of light in living organisms as the result of
a chemical reaction with little or no heat produced (ex. Fireflies)
Bioluminescence
WAYS TO GAIN ENERGY &
PRODUCE LIGHT
 Triboluminescence – production of light from friction as a result of
scratching, crushing, or rubbing certain crystals
 First noticed by Francis Bacon in 1620
WAYS TO GAIN ENERGY &
PRODUCE LIGHT
 Light-Emitting Diode (LED) – light produced as a result of an electric
current flowing in semi-conductors in one direction ex:silicon
 Regular conductors allow electrons to flow in either direction
 Benefits of LED – less heat produced, more efficient