Post on 23-Dec-2015
Light travels in straight lines:
Laser
Light travels VERY FAST – around 300,000 kilometres per second.
At this speed it can go around the world 8 times in one second.
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.
Luminous objects Reflectors
Shadows
Shadows are places where light is “blocked”:
Rays of light
Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of incidence
Angle of reflection
Mirror
The Law of ReflectionThe Law of Reflection
Angle of incidence = Angle of reflectionAngle of incidence = Angle of reflection
In other words, light gets reflected from a surface at ____ _____ angle it hits it.
The same !
!!
Smooth, shiny surfaces have a clear reflection:
Rough, dull surfaces have a diffuse reflection.
Diffuse reflection is when light is scattered in different directions
RedOrangeYellowGreenBlue
IndigoViolet
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 and green:Adding blue and
red makes magenta (purple)
Adding blue and green makes cyan
(light blue)
Adding all three makes white again
Adding red and green makes yellow
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 white hat would reflect all seven colours:
A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and
blue):
Purple light
White
light
If we look at a coloured object in coloured light we see something different. For example, consider a football kit:
White
light
Shorts look blue
Shirt looks red
In different colours of light this kit would look different:
Red
lightShirt looks red
Shorts look black
Blue
light
Shirt looks black
Shorts look blue
Be TRANSMITTED laser aimed at water or
glassBe REFLECTED
specular reflection of light by a mirror
diffuse reflection of the light in this room off all the other students
reflection is re-radiation of light by the electrons in the reflecting material
Be ABSORBED Cyan light shining on a
red apple is absorbed by electrons in the apple
Something new!!A light wave shining on
molecules in the air or plastic or other “transparent” materials can be:
SCATTERED Light ray moves over to
the side in all directions rather than forward, backward or being absorbed.
Intensity of the scattered light can depend on wavelength
Speed of light in empty space is c = 3 x 108 meters/sec
RayWaveform
Amplitude(maximum height)The intensity of the light is proportional to the amplitude squared. Large amplitude means bright light. Low amplitude means dim lightW
avel
engt
h
Light consists of electric (and magnetic) fields moving through space at the speed of light
Human eyes are only able to process information from the visible part of the spectrum
Toward longer wavelengths, the spectrum includes infrared light, microwaves, and radio
Toward shorter wavelengths, the spectrum includes ultraviolet light, X-rays, and gamma rays
All of these are forms of electromagnetic radiation
What we see as white light is actually made up of a continuum of components
Traditionally, we break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV)
There is actually a continuous transition of color, each with its own wavelength and frequency
Red light has an approximate wavelength of 7.0 x 10-
7 m and a frequency of 4.3 x 1014 Hz
Violet light has an approximate wavelength of 4.0 x 10-7 m and a frequency of 7.5 x 1014 Hz
Rayleigh Mie Geometric
Blue skyRed SunsetBlue water (from underwater)
The shorter the wavelength, the more light is scattered blue is scattered more than
red. this is why the sky is blue and
sunsets are red.
Think of white light from sun as a mixture of R, G and B
Blue is scattered the most so sky looks blue when we look away from the sun
Earth
Atmosphere
Rays from Sun (not scattered)
White or yellow
•Larger particles scatter red as well as blue and hence look white.
•Dust or smoke•Clouds; •Milk;
•There are many other types of scattering…
Explains scattering around larger droplets such as Corona around the sun or moon, and similar phenomena.