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