# Reflection and Refraction. 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.

## Presentation on theme: "Reflection and Refraction. 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."— Presentation transcript:

Reflection and Refraction

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 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: Homework Home

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 SourcesIlluminated Source Sun Light Bulb Fire Moon Earth Humans

Reflection Reflection from a mirror: Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror

The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at the same angle it hits it. The same !!!

Specular 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

Refraction 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

Plane Mirror Is 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 Mirrors Concave Mirrors have edges that are curved toward the observer. The image will be upside-down.

Convex Mirrors Convex Mirrors have edges that are curved away from the observer. Object is right side-up.

Using mirrors Two examples: 1) A periscope 2) A car headlight

Concave Lenses Thinner in the middle than at the edges. Beams bend outward when leaving the lens.

Convex Lenses Thicker in the center than at the edges. Beams come together when leaving the lens.

Glasses Nearsighted EyeFarsighted Eye Uses a concave lens to correct Uses a convex lens to correct

Color

Adding colors White 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 Colors The colors that are formed when the primary color of light are mixed. Red + Green = Yellow Blue + Green = Cyan Red + Blue = Magenta Secondary Colors

Complementary 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

Color 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 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 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 light Shirt 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 filters Filters can be used to “block” out different colors of light: Red Filter Magenta Filter

Red Magenta White Yellow BlueGreen Cyan

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