Light and the Electromagnetic Spectrum
Light Phenomenon Isaac Newton (1642-1727) believed light consisted of particles By 1900 most scientists believed that light behaved as a wave.
The Electromagnetic Spectrum The electromagnetic spectrum represents the range of energy from low energy, low frequency radio waves with long wavelengths up to high energy, high frequency gamma waves with small wavelengths.
RedOrangeYellowGreenBlueIndigoViolet Visible light is a small portion of this spectrum. This is the only part of this energy range that our eyes can detect. What we see is a rainbow of colors. RedOrangeYellowGreenBlueIndigoViolet ROY G BIV
Frequency Ranges Wavelengths 104 101 1 10-2 10-5 10-6 10-8 10-10 10-12 104 101 1 10-2 10-5 10-6 10-8 10-10 10-12 Frequencies (cycles per sec) 3 x 106 3 x 1010 3 x 1014 3 x 1016 3 x1018 3 x10 22
Frequency Ranges of Visible Light Red light has a frequency of roughly 4.3 × 1014 Hz, and a wavelength of about 7.0 × 107 m (700nm). Violet light, at the other end of the visible range, has nearly double the frequency—7.5 × 1014 Hz—and (since the speed of light is the same in either case) just over half the wavelength— 4.0 × 107 m (400nm).
Speed of light=wavelength X frequency The product of wavelength and frequency always equals the speed of light. C = λν Speed of light=wavelength X frequency Why does this make sense? NOTE: c is a constant value= 3.00 x 108 m/s
List the known info List the unknown PROBLEMS Calculate the wavelength of yellow light emitted from a sodium lamp if the frequency is 5.10 x 1014 Hz (5.10 x 1014 s-1) List the known info List the unknown c = 3.00 x 1010 cm/s wavelength (λ) = ? cm Frequency (v) = 5.10 x 1014 s-1 C = λv λ = c v λ = 3.00 x 1010 cm/s = 5.88 x 10-5 cm 5.10 x 1014 s-1
YOUR TURN 1- What is the wavelength of radiation with a frequency of 1.50 x 1013 s-1?
The colors we see in objects are the colors that are reflected, all other colors are absorbed. A red t-shirt appears red because red is reflected to our eyes and the other colors are absorbed. When all colors are being reflected we see white light (white isn’t really a color)
When all wavelengths of light are being absorbed we see black (black also, isn’t really a color) A false-color image is made when the satellite records data about brightness of the light waves reflecting off the Earth's surface.
The true color image on left is how our eyes would see it. The false color image is enhanced to bring out subtle details to make it easier to study Uranus’ cloud structure.
Atoms and Light The movement of electrons inside of atoms produces light and other electromagnetic radiation. Sunlight produces every color in the rainbow but… Each element gives off only certain frequencies of light, called spectral lines. In effect each element has its own signature of spectral lines allowing us to identify which element we have or what stars are made of.
Below is a picture of the spectral lines given off by hydrogen Below is a picture of the spectral lines given off by hydrogen. Note there are 3 different frequencies.
The emission spectra makes it possible to identify inaccessible substances. Most of our knowledge of the universe comes from studying the emission spectra of stars. Below is the spectra of a few more elements. Helium
Neon Argon
Electromagnetic Waves & the Electromagnetic Spectrum
Electromagnetic Waves Transverse waves without a medium! (They can travel through empty space)
They travel as vibrations in electrical and magnetic fields. Have some magnetic and some electrical properties to them.
When an electric field changes, so does the magnetic field When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other. RESULT-An electromagnetic wave.
Electromagnetic waves travel VERY FAST – around 300,000 kilometres per second (the speed of light). At this speed they can go around the world 8 times in one second.
Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency GAMMA RAYS ULTRAVIOLET RAYS RADIO WAVES INFRARED RAYS X-RAYS MICROWAVES VISIBLE LIGHT
Notice the wavelength is long (Radio waves) and gets shorter (Gamma Rays)
RADIO WAVES Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.
Global Positioning Systems (GPS) measure the time it takes a radio wave to travel from several satellites to the receiver, determining the distance to each satellite.
A radio picks up radio waves through an antenna and converts it to sound waves. Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency.
(MAGNETIC RESONACE IMAGING) MRI (MAGNETIC RESONACE IMAGING) Uses Short wave radio waves with a magnet to create an image.
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.
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.
Shorter wavelength and higher frequency than microwaves. INFRARED RAYS Infrared= below red Shorter wavelength and higher frequency than microwaves.
You can feel the longest ones as warmth on your skin Warm objects give off more heat energy than cool objects.
Thermogram—a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off. Heat lamps give off infrared waves. 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) 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.
ULTRAVIOLET RAYS Shorter wavelength and higher frequency than visible light Carry more energy than visible light
Used to kill bacteria. (Sterilization of equipment)
Too much can cause skin cancer. Use sun block to protect against (UV rays)
Causes your skin to produce vitamin D (good for teeth and bones)
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 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)
Used by engineers to check for tiny cracks in structures. The rays pass through the cracks and the cracks appear dark on film.
Shorter wavelength and higher frequency than X- rays 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.
The Incredible Hulk was the victim of gamma radiation.
Exploding nuclear weapons emit gamma rays.
Brief SUMMARY A. All electromagnetic waves travel at the same speed. (300,000,000 meters/second) in a vacuum. B. They all have different wavelengths and different frequencies. Long wavelength-lowest frequency Short wavelength highest frequency The higher the frequency the higher the energy.