Light In this presentation: 1)What is light? 2)Electromagnetic Spectrum 3)Interactions of Light 4)Color

What is light? Light is an electromagnetic wave! An electromagnetic wave is a wave that travels through empty space or matter and consists of changing electric and magnetic fields!

Properties of Light Light travels in straight lines: Laser

Light travels VERY FAST – around 300,000 km/sec. This is 880,000 times faster than sound. At this speed it can go around the world 8 times in one second.

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.

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

Properties of Light summary 1)Light travels in straight lines 2)Light travels much faster than sound 3)Shadows are formed when light is blocked by an object

2. The Electromagnetic Spectrum Entire range of EM waves! Divided into regions according to wavelength Where is the highest energy?

VISIBLE LIGHT:NARROW RANGE OF WAVELENGTHS between 400nm and 700nm; the ONLY wavelengths that humans can see LONGEST TO SHORTEST WAVELENGTH Red Orange Yellow Green Blue Indigo Violet Remember: Roy G. Biv

Electromagnetic Spectrum The electromagnetic spectrum is arranged from long to short wavelength or from low to high frequency

3. INTERACTIONS OF LIGHT REFLECTION/LAW OF RELFECTION TYPES OF REFLECTION LIGHT SOURCE V. REFLECTED LIGHT ABSORPTION SCATTERING REFRACTION DIFFRACTION

We see things because they reflect light into our eyes: Homework

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 !!!

Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

Luminous and non-luminous objects A luminous object is one that produces light. An illuminated object is one that reflects light. Luminous objectsIlluminated FIREFLY SUN LIGHT BULB A VISIBLE OBJECT THAT IS NOT A LIGHT SOURCE

ABSORPTION THE ABSORPTION OF LIGHT ENERGY BY MATTER-CAUSES LIGHT TO BECOME DIMMER. THE FARTHER LIGHT TRAVELS FROM THE SOURCE, THE DIMMER IT BECOMES

SCATTERING INTERACTION THAT CAUSES LIGHT TO CHANGE DIRECTION ALLOWS YOU TO SEE OBJECTS OUTSIDE THE BEAM, BUT BECAUSE LIGHT IS SCATTERED, BEAM BECOMES DIMMER.

REFRACTION AND COLOR SEPARATION Red Orange Yellow Green Blue Indigo Violet Violet light, which has a shorter wavelength, is refracted more than red light

DIFFRACTION LIGHT CANNOT BEND VERY MUCH BY DIFFRACTION UNLESS IT PASSES THROUGH A VERY NARROW OPENING OR AROUND A SMALL BARRIER. LIGHT CANNOT DIFFRACT VERY MUCH AROUND LARGE OBJECTS

TRANSMISSION LIGHT PASSES THROUGH MATTTER. ALL OF THE LIGHT THAT REACHES YOUR EYES IS TRANSMITTED THROUGH AIR.

3. 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.

TYPES OF MATTER 1.TRANSPARENT-LIGHT IS TRANSMITTED THROUGH EASILY 2.TRANSLUCENT- TRANSMITS AND SCATTERS 3.OPAQUE- DOES NOT TRANSMIT LIGHT

How is color determined? The color an opaque object appears depends on the colors of light it reflects. For example, the book only reflects red light so we see it as red! White light Only red light is reflected

Transparent/Translucent Color transmitted is color you see. All other colors are absorbed.

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

Using colored light If we look at a colored 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 light Shirt looks red Shorts look black Blue light Shirt looks black Shorts look blue

The white hair reflects all the light….the black hair absorbs all the light

PIGMENTS A PIGMENT is a material that gives a substance its color by absorbing some colors of light and reflecting others. Chlorophyll is a pigment as is melanin (skin pigment) and paint colors

MIXING PIGMENTS WHEN YOU MIX PIGMENTS TOGETHER, MORE COLORS OF LIGHT ARE ABSORBED OR TAKEN AWAY. MIXING PIGMENTS IS CALLED COLOR SUBTRACTION