Light

clappergappawpawUrban and Civil

Nov 16, 2013 (3 years and 8 months ago)

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Sound Waves
Compresssions
Rarefractions
Harmonics
The Ear
What
is light?
WHAT IS LIGHT?
Light
is a form of
electromagnetic radiation
which is
transmitted in waves…

What is light?
WHAT IS LIGHT?

Electromagnetic radiation


Electromagnetic radiation
waves
, as their names suggest
are fluctuations of
electric
and
magnetic
fields, which can
transport energy from one
location to another.

WHAT IS LIGHT?


Electromagnetic radiation
is produced by the
oscillation
or
acceleration
of an electric charge;


Electromagnetic waves
do not need to be transmitted via a
material - they can travel through interplanetary and interstellar
space from the Sun and stars to the Earth.

Electromagnetic radiation
WHAT IS LIGHT?

Electromagnetic radiation
It only takes 8.3
minutes for light to
travel from the sun
to the earth…

WHAT IS LIGHT?


All
electromagnetic radiation
travels at
the
speed of light
– this is approximately
300,000 kilometres per second -

theoretically – the fastest speed in the
universe!

Electromagnetic radiation
That’s equivalent to traveling around the
earth seven times in one second…
WHAT IS LIGHT?


Electromagnetic radiation
can be arranged in a
spectrum
that extends
from waves of extremely high frequency and short wavelength to
extremely low frequency and long wavelength;


Within this range is a special segment of radiation which is capable of
stimulating receptors in the human eye;


This special segment within the
electromagnetic spectrum
is called
visible energy

or
visible light
.

Electromagnetic radiation
WHAT IS LIGHT?
As we can see
visible
light
is only a very small part
of the
electromagnetic spectrum
The electromagnetic spectrum
low

frequency
&
long

wavelengths
high

frequency
&
short

wavelengths
WHAT IS LIGHT?
Examples from the
electromagnetic spectrum…
WHAT IS LIGHT?
Examples from the
electromagnetic
spectrum…
WHAT IS LIGHT?

Visible light


Visible light
is no different from the other parts of the
electromagnetic spectrum;


However
, the human eye has evolved to detect
visible waves
;


Some people could argue that it is no accident that humans
evolved to ‘see’ light – the detection of light by humans is a powerful
tool for enabling us to investigate the universe that exists around us.
Perception
WHAT IS LIGHT?

Visible light


The special segment of
visible energy
or
visible light
that can be
detected by the human eye
consists of extremely fast
oscillations
of an
electromagnetic field in a particular range of frequencies of between
about
380 and 780 nanometres (nm);


Within this narrow band of
visible light
, each individual colour has its
own
wavelength
.
WHAT IS LIGHT?

Visible light


Each
wavelength

is measured in
nanometers
or ‘nm’ – a
nanometer
is extremely small – about one billionth of a meter;


We perceive these different
wavelengths
of light as the rainbow
hues of colours.
WHAT IS LIGHT?


Light with a wavelength of 400 nm is perceived as being
violet
;


Light with a wavelength of 500 nm is perceived as being
green
;


Light with a wavelength of 600 nm is perceived as being
orange;


Light with a wavelength of 700 nm is perceived as being

red

The electromagnetic spectrum
low

frequency
&
long

wavelengths
high

frequency
&
short

wavelengths

Visible light
WHAT IS LIGHT?


When the whole range of
wavelengths is present, the
mixture of colors produced is
described as
white light
;


White light
is what we actually
see coming from the sun.

Colour perception
WHAT IS LIGHT?


However, everyday terminology for describing colour is very
subjective
:
what may appear
orangey red
to one person,
may appear to be
reddish orange
to another.


Our
colour perceptions
are very often
subjective
!

We’ll cover this in more detail in a further lecture!

Visible light
WHAT IS LIGHT?


Light and vision are totally dependent upon each other -
We cannot see without light…

and
light cannot be seen without vision..
.
WHAT IS LIGHT?


Light is not
visible
by itself - light falling on an object or colour
makes that object or colour
visible
;


The appearance, definition and character of objects and spaces
are greatly affected by the kind of light that makes them
visible
.

Visible light
WHAT IS LIGHT?


When light strikes an object it is:
-

Re-emitted;
-

Absorbed or;
-

Allowed to pass through.
This depends on the degree
of
transparency
or
opacity
of
the material which makes up
the object.

Visible light
Re-emitted light
absorbed light
light passing through
WHAT IS LIGHT?
The concept of light thus combines exact
scientific phenomena
with
subjective perceptions

since human eyes and brains behave and
respond in different ways
Firstly we will need to look at
natural light
and how it affects
what we see around us… but we’ll do that next time!

Visible light
The Electromagnetic Spectrum
and the Earth