Properties of Light and the Electromagnetic Spectrum Dan Flavin Untitled (Marfa Project) - 1996

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. All electromagnetic waves travel at the speed of light. Visible light is just one type of electromagnetic wave.

Dual Nature of Light

Light is a Particle (Photon) 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

Photoelectric Effect

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

Light is a Wave Click here for video Click here for video

Polarization

Polarization

Polarization Polarization is another wave property of light. The fact that light shows polarization tells us that light is a transverse wave. Most of the light that you see is unpolarized. That does not mean the light has no polarization. Unpolarized light is actually an equal mixture of all polarizations. We call ordinary light unpolarized because no single polarization dominates the mixture.

The Electromagnetic Spectrum 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. http://www.walter-fendt.de/ph14e/emwave.htm

Visible Light as Part of the EM Spectrum click here for video

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 Electromagnetic Spectrum 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.

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 Animation—View a Galaxy at different wavelengths

B. They all have different wavelength and different frequencies. 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.