Reflection and Reflection and RefractionRefraction
Light travels VERY FAST – around 300,000,000 m/s
(that’s 670,000 mph)
At this speed it can go around the world 8 times in one second.
Speed of LightSpeed of Light
Our nearest spiral galaxy is Andromeda. It is 2.5 million light years away
Light is so fast, physicists measure
light with ‘light years’.
A light year is the distance that light travels in one year.
5.8 Trillion Miles in a Year
Light travels much faster than sound. For example:
Thunder and lightning start at the same time, but we will see the lightning first.
We see things because the object reflects light into our
eyes:
HomeworkHome
There are two types of objects when dealing with light
A luminous source is one that produces light.
A illuminated source is one that reflects light.
Luminous Sources Illuminated Source
Sun
Light Bulb
Fire
Moon
Earth
Humans
ReflectionReflection
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 Angle of incidence = Angle of reflectionreflection
In other words, light gets reflected from a surface at the same angle it hits it.
The same !
!!
Specular vs. Diffuse ReflectionSpecular vs. Diffuse Reflection
Smooth, shiny surfaces have a specular reflection:
Rough, dull surfaces have a diffuse reflection.
Diffuse reflection is when light is scattered in different directions
RefractionRefraction
Refraction is when waves speed up or slow down due to traveling in a different medium.
EXAMPLE: Pencil in the Oil
In this case the light rays are slowed down by the oil and are bent, causing the pencil to look odd. The two mediums in this example are air and oil.
Mirrors and Lenses Mirrors and Lenses
Plane MirrorPlane MirrorIs a flat, smooth surface from which light
is reflected by smooth reflection.
An object is a source of light rays that are reflected by the surface of the mirror.
Looking at yourself in a plane mirror, your image appears to be the same distance behind the mirror as you are in front of the mirror.
Concave MirrorsConcave Mirrors
Concave Mirrors have edges that are curved toward the observer.
The image will be upside-down.
Convex MirrorsConvex Mirrors
Convex Mirrors have edges that are curved away from the observer.
Object is right side-up.
Using mirrorsUsing mirrorsTwo examples:
1) A periscope
2) A car headlight
Concave LensesConcave Lenses
Thinner in the middle than at the edges.
Beams bend outward when leaving the lens.
Convex LensesConvex Lenses
Thicker in the center than at the edges.
Beams come together when leaving the lens.
GlassesGlasses
Nearsighted Eye Farsighted Eye
Uses a concave lens to correct
Uses a convex lens to correct
ColorColor
Adding colorsAdding colorsWhite light can be split up to make separate
colors. These colors can be added together again.
The primary colors 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
Secondary ColorsSecondary Colors
The colors that are formed when the primary color of light are mixed.
Red + Green = YellowBlue + Green = CyanRed + Blue = Magenta
Secondary Colors
Complementary ColorsComplementary Colors
The colors that can be combined to form white light.
Yellow (green + red) + Blue = White
Magenta (blue + red) + Green = White
Cyan (blue + green) + Red = White
ColorColor
White (visible) light is not a single color; it is made up of a mixture of the seven colors of the rainbow.
We can demonstrate this by splitting white light with a prism.
Seeing ColorSeeing Color An object looks a certain color because it
reflects that color light to our eyes and absorbs all other colors.
For example, a red book only reflects red light:
White
light
Only red light is
reflected
An object appears white because it reflects all colors from white light:
The Color White
White
light
White
light
The Color Black
Black can be thought of as a lack of color.
A black object absorbs all white light and reflects no color at all
Shadows
Shadows are places where light is “blocked”:
Rays of light
Using colored lightUsing colored light
If we look at a colored object in colored light we see something different. For example:
White
light
Shorts look blue
Shirt looks red
In different colors of light this kit would look different:
Red
lightShirt looks red
Shorts look black
Blue
light
Shirt looks black
Shorts look blue
A white hat would reflect all seven colors:
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
Using filtersUsing filtersFilters can be used to “block” out different colors of
light:
Red Filte
r
Magenta
Filter
Red
Magenta
White
Yellow
Blue Green
Cyan