Properties of Light

The speed of light  The speed at which light travels through air is approximately 300 million meters per second.  Light travels almost a million times faster than sound.

—travels in straight lines at great speeds —is reflected from mirrors in a predictable way —Has energy in discrete packets, momentum —Photoelectric effect Newton observed that the reflection of light from a mirror resembles the rebound of a steel ball from a steel plate Light is a Particle (Photon)

Light is a Wave  Thomas Young showed that light is a wave, because it —undergoes diffraction and interference (Young’s double-slit experiment)  Wavelength  Amplitude A  Frequency f

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Polarization

18.2 Polarization  Polarization is another wave property of light.  The fact that light shows polarization tells us that light is a transverse wave.

 The energy field created by electricity and magnetism can oscillate and it supports waves that move.  These waves are called electromagnetic waves. The Electromagnetic Spectrum

 Electromagnetic waves have both an electric part and a magnetic part and the two parts exchange energy back and forth.  A 3-D view of an electromagnetic wave shows the electric and magnetic portions. The Electromagnetic Spectrum

RADIO WAVES  A. Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.  B. A radio picks up radio waves through an antenna and converts it to sound waves.  C. Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency.  D. MRI (MAGNETIC RESONACE IMAGING) —Uses Short wave radio waves with a magnet to create an image

MRI of the Brain

AM=Amplitude modulation—waves bounce off ionosphere can pick up stations from different cities. (535kHz-1605kHz= vibrate at 535 to 1605 thousand times/second) +

FM=Frequency modulation—waves travel in a straight line & through the ionosphere-- lose reception when you travel out of range. (88MHz-108MHz = vibrate at 88million to 108million times/second) +

MICROWAVES  Microwaves—have the shortest wavelengths and the highest frequency of the radio waves. —Used in microwave ovens. Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food. —Used by cell phones and pagers. —RADAR (Radio Detection and Ranging) Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.

INFRARED RAYS  Infrared= below red  Shorter wavelength and higher frequency than microwaves.  You can feel the longest ones as warmth on your skin  Heat lamps give off infrared waves.  Thermogram—a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off. Therefore people give off infrared rays.

VISIBLE LIGHT  Shorter wavelength and higher frequency than infrared rays.  Electromagnetic waves we can see.  Longest wavelength= red light  Shortest wavelength= violet (purple) light  When light enters a new medium it bends (refracts). Each wavelength bends a different amount allowing white light to separate into it’s various colors ROYGBIV.

 The higher the frequency of the light, the higher the energy of the wave.  Since color is related to energy, there is also a direct relation between color, frequency, and wavelength. The Electromagnetic Spectrum

ULTRAVIOLET RAYS  Shorter wavelength and higher frequency than visible light  Carry more energy than visible light  Used to kill bacteria. (Sterilization of equipment)  Causes your skin to produce vitamin D (good for teeth and bones)  Used to treat jaundice ( in some new born babies.  Too much can cause skin cancer.  Use sun block to protect against (UV rays)

X- RAYS  Shorter wavelength and higher frequency than UV- rays  Carry a great amount of energy  Can penetrate most matter.  Bones and teeth absorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed)  Too much exposure can cause cancer —(lead vest at dentist protects organs from unnecessary exposure)

GAMMA RAYS  Shorter wavelength and higher frequency than X- rays  Carry the greatest amount of energy and penetrate the most.  Used in radiation treatment to kill cancer cells.  Can be very harmful if not used correctly.

Using the EM waves to view the Sun AnimationAnimation—View a Galaxy at different wavelengths

 Brief SUMMARY  A. All electromagnetic waves travel at the same speed. (300,000,000 meters/second in a vacuum.  B. They all have different wavelength and different frequencies. —Long wavelength-  lowest frequency —Short wavelength  highest frequency —The higher the frequency the higher the energy.

How the human eye sees color  The retina in the back of the eye contains photoreceptors.  These receptors release chemical signals.  Chemical signals travel to the brain along the optic nerve. optic nerve

16.2 How we see other colors  The three color receptors in the eye allow us to see millions of different colors.  The additive primary colors are red, green, and blue.  We don’t see everything white because the strength of the signal matters.  All the different shades of color we can see are made by changing the proportions of red, green, and blue.

How we see the color of things When we see an object, the light that reaches our eyes can come from two different processes:  The light can be emitted directly from the object, like a light bulb or glow stick.  The light can come from somewhere else, like the sun, and we see the objects by reflected light.

Filtered Light

How we see the color of things  Colored fabrics and paints get color from a subtractive process.  Chemicals, known as pigments, in the dyes and paints absorb some colors and allow the color you actually see to be reflected.  Magenta, yellow, and cyan are the three subtractive primary colors.