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# Light 1)Properties of light 2)Reflection 3)Colors 4)Refraction.

## Presentation on theme: "Light 1)Properties of light 2)Reflection 3)Colors 4)Refraction."— Presentation transcript:

Light 1)Properties of light 2)Reflection 3)Colors 4)Refraction

LIGHT: What Is It? Light Energy –Atoms As atoms absorb energy, electrons jump out to a higher energy level. Electrons release light when falling down to the lower energy level. –Photons - bundles/packets of energy released when the electrons fall. Light: Stream of Photons

Moving photon creates electric & magnetic field –Light has BOTH Electric & Magnetic fields at right angles! –Energy is perpendicular to direction of motion Transverse Waves

Electromagnetic Spectrum

Invisible Spectrum –Radio Waves –Infrared Rays –Ultraviolet rays –X-Rays –Gamma rays

Visible Spectrum – Light we can see –Largest to Smallest Wavelength. –Roy G. Biv – Acronym for Red, Orange, Yellow, Green, Blue, Indigo, & Violet. Don’t forget those sexy birds…

Part 1 – Properties of Light Light travels in straight lines: Laser

Light travels VERY FAST – around 300,000 kilometres per second. C = 3.0 x 10 8 m/s At this speed it can go around the world 8 times in one second. Speed of light = frequency x wavelength C = f λ

What is the wavelength range for the FM radio band (88 MHz-108 MHz)? C = f λ C/f = λ 3.0 x 10 8 m/s / 88 x 10 6 = 3.4 m 3.0 x 10 8 m/s / 108 x 10 6 = 2.78 m The portion of the visible spectrum appears brightest to humans around 560 nm in wavelength. What is the frequency of 560 nm light? C = f λ C/λ = f 3.0 x 10 8 m/s / 560 x 10 -9 = 5.4 x 10 14 Hz

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

Shadows Shadows are places where light is “blocked”: Rays of light

Brightness -Brightness decreases by the square of the distance from the source. -THE FURTHER YOU ARE FROM THE LIGHT THE LESS BRIGHT IT IS -If you move twice as far away from the light source, ¼ as much light falls

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 5)Brightness affected by distance

Reflection -DEFINITION:the turning back of an electromagnetic wave at the surface of a substance -Most substances absorb some light and reflect the rest. (no surface is a perfect reflector)

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

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

Part 2 - 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 ____ _____ angle it hits it. The same !!!

Flat Mirrors Object distance (p): the distance the object is from the mirror Image distance (q): the distance the image appears to be behind the mirror’s surface The object and image distances are equal. The image and the object are the same size.

Virtual image A flat mirror always forms a virtual image. You can only see this behind the mirror Cannot be displayed on a physical surface

Color White 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: This is how rainbows are formed: sunlight is “split up” by raindrops.

The colors of the rainbow: Red Orange Yellow Green Blue Indigo Violet

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

Seeing color The color an object appears depends on the colors 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 colors: A pair of purple britches would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light White light

Using colored light If we look at a colored object in colored light we see something different. For example, consider a soccer jersey: 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

Some further examples: ObjectColor of light Color object seems to be Red socks Red BlueBlack GreenBlack Blue teddy RedBlack Blue Green Green camel Red Blue Green Magenta book Red Blue Green

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

Investigating filters Color of filterColors that could be “seen” Red Green Blue Cyan Magenta Yellow

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