Transcript Where does light come from?

Where does light come from?
The SUN!!
The sun is a star located 1.50 x 108, or 1 Astronomical Unit., away
from Earth. It provides energy in the form of light through a process
called nuclear fusion. Nuclear fusion occurs when two atoms that
naturally repelled each other are pulled together by a superior force
and the atoms fuse together. The sun’s enormous gravitational force
pulls hydrogen atoms together where they fuse to form a helium
atom. We then get energy in the form of light and heat.
• The sun provides the energy that enables life
on Earth.
Properties of Light
• Light travels in straight lines:
Laser
• Light travels VERY FAST – 3.0 x
10^8m/s
= 300,000 kilometres per second.
At this speed it
can go around the
world 7.5 times in
one second.
• Light travels much faster than sound. For
example:
1) Thunder and lightning
start at the same time,
but we will see the
lightning first.
2) When a starting pistol is
fired we see the smoke
first and then hear the
bang.
• We see things because they reflect
light into our eyes:
Homework
• Luminous and non-luminous objects
A luminous object is one that produces light.
A non-luminous object is one that reflects
light.
• Shadows
Shadows are places where light is “blocked”:
Properties of Light summary
1) Light travels in straight lines
2) Light travels much faster than sound
3) We see things because they reflect light into
our eyes
4) Shadows are formed when light is blocked by
an object
History
• Unlike heat energy which requires a and sound (a
physical substance) to move, light does not
• Light is transferred through radiation in a vacuum
at the speed of light (3.0X108 m/s)
• Light is therefore classified as an Electromagnetic
Wave
Modern electromagnetic waves
• Today we have identified many types of
electromagnetic waves which makes up our
electromagnetic spectrum.
Eureka Video - Radiation Spectrum
Modern View Continued
As we decrease wavelength, we
increase frequency and energy
The Visible Light Spectrum
• Different colours have different wavelengths!
The Surprising Universe
• Today Scientists use different portions of the
electromagnetic spectrum to collect and
analyze data about stars and galaxies
• This provides them with completely different
views compared with using visible light only
http://spaceplace.nasa.gov/en/kids/sirtf1/sirtf_action.shtml
The Surprising Universe
Essential Knowledge, Skills, and
Processes
• Analyze the effects of a prism on white light
and describe why this occurs. Explain why a
rainbow occurs.
Answer: different colors
have different
wavelengths which
bend differently as they
pass through the prism.
http://www.physicslessons.com/exp33.htm
Colour
• White light is not a single colour; it is made
up of a mixture of the seven colours of the
rainbow.
We can demonstrate this by
splitting white light with a
prism:
This is how rainbows are
formed: sunlight is split up by
raindrops.
The colours of the rainbow:
• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet
Prisms
• What happens when you place two prisms
next to each other?
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/newton/
Adding colours
• White light can be split up to make separate colours.
These colours can be added together again.
• The primary colours of light are red, blue, green:
Adding blue and red
makes magenta
(purple)
Adding red and
green makes
yellow
Adding blue and green
makes cyan (light blue)
Adding all three
makes white
again
Colour Adding and Subtracting
• http://www.physicslessons.com/exp35.htm
Seeing colour
• The colour an object appears depends on the colours of
light it reflects
For example, a red book only reflects red light:
White
light
Only red light is
reflected
A pair of purple pants would reflect purple light (and red and blue,
as purple is made up of red and blue):
Purple light
A white hat would reflect all the colours:
White
light
Using coloured light
• If we look at a coloured object in coloured
light we see something different. For
example, consider a soccer uniform:
Shirt looks red
White
light
Shorts look blue
• In different colours of light this uniform would look different:
Red
Shirt looks red
light
Shorts look black
Shirt looks black
Blue
light
Shorts look blue
Using filters
• Filters can be used to “” out different colours of light:
Red Filter
Magenta
Filter