Applied Science III Mr. Finau

What exactly is light?  Energy  Einstein theorized that light consists of mass-less bundles of concentrated electromagnetic energy later called “photons”

How does it travel?  Physicists now agree light has a “dual nature” – part particle…part wave  Particles travel in straight lines  Electromagnetic waves travel and expand through space using itself as a medium

Double Slit Experiment

What are some properties of waves?  Amplitude – maximum change in a wave  Wavelength – the length of a particular wave  Frequency – the number of waves that occur in a second  Speed – how fast a particular wave travels through a medium

Is visible light the only form of electromagnetic waves?  No, visible light is only a very small portion of what’s known as the “electromagnetic spectrum”, which includes (in order)  Radiowaves  Microwaves  Infrared waves  Visible Light  Ultraviolet waves  X-rays  Gamma Rays

What are Ultraviolet waves most typically known for?  Causing sun burns! But why?  Ultraviolet waves carry more energy with them than visible light

What does that mean for X-rays and Gamma rays?  They carry even more energy and can be harmful if overly exposed  This is why lead is often used to protect from radiation; lead is a very dense material that blocks most types of radiation

So what happens to the energy of a wave as the frequency increases?  The energy of the waves increases as the frequency increases  The more energy a wave has increases the effects it has on everything it comes in contact with

What are Infrared waves typically associated with?  Heat  Heat gives off infrared rays, which can be detected with infrared sensors  Heat lamps in restaurants emit a large amount of infrared waves to keep food warm, which is why they appear reddish in color

How fast does it travel?  In a vacuum: 3 X 10 8 m/s = 671,080,887 mph  originally measured by Christian Huygens in 1675 by measuring the orbit of one of Jupiter’s moon

How long does it take for light to travel 1 light-year?  One Year  Light-year is a unit of measurement of the distance light travels in a year

Does light travel at the same rate through all materials?  No, through each material, light travels at different rates depending on the “index of refraction”  Index of refraction – the ratio between the speed of light in a vacuum and the speed of light in that material

What is refraction?  Refraction – the bending of light depending on the makeup of the substance and the change in speed of light

Bill Nye on Light

When light travels through a material easily, what is it called? Examples?  Transparency – the ability of a material to allow light to pass through it  Examples include glass, water, clear plastics, plexi-glass

When light cannot travel through a material, what is it called? Examples?  Opaque – ability of a material to absorb light and block it from traveling through it  Examples include wood, stone, people, etc.

What happens to light hitting shiny metals?  Reflection – process where light is reemitted from a surface it comes in contact with  Energy excites surface electrons of metal, but bounces off at the same angle it strikes the surface

What is light scattering?  When white light from the sun hits the atmospheric particles and molecules, it scatters in different directions  Scattering is the process by which radiation is caused to move in different directions after interacting with molecules

What color does light contain when it is emitted from the sun?  All of the colors of the spectrum – known as white light

Why is the sky blue?  Light with higher frequencies are scattered the most while low frequencies are scattered the least?  Since human eyes are not very sensitive to detecting violet light, what is the next color that is observed?  BLUE!

How do you get colors from light reflecting off of objects?  When light reflects off of an object, every color from the spectrum is absorbed except for the colors of light that you see with your eyes, for example…  Most plants contain Chlorophyll, which absorb most energies of light to use for photosynthesis. The only color of light that isn’t absorbed is…  Green, which is why plants appear green.

When a car is outside on a sunny day, which gets hotter - a white car or a black car? Why?  The black car gets much hotter  If white light hits a white car, most of the light is reflected off of the surface  If white light hits a black car, most of the light is absorbed in the surface, absorbing all of the energy causing it to get warmer.

If there’s glass in front of a light source, why is it sometimes a particular color?  Transmission – property of a substance to allow the passage of light, with some or none of the light being absorbed  Pigment – the material in a glass that selectively absorbs color light  A red glass absorbs all light except what color?

What are the primary colors of light?  Red, Blue, Green  Color television is based on the ability of the human eye to see and interpret combinations of three colors as a variety of colors

What are the complementary colors of light?  Red + Green = Yellow  Red + Blue = Magenta (kind of a pinkish color)  Blue + Green = Cyan (a light bluish)

Stare at the center dot

What color is the afterimage flag?

How is this effect created?  Retinal Fatigue – when eye receptors send a weaker signal to the brain due to fatigue caused by temporary overuse DON’T WRITE THE FOLLOWING  In this activity, after staring at the image, those colors of the flag are not transmitted to the brain by the receptor, so for instance, white light from the board minus the cyan color gives the red of the stripes

Video about the Power of Light