The Physics of the Electromagnetic Spectrum or Radiant Energy *** Light, Heat, and Radiation
Light = EM Spectrum The terms light, radiation, and electromagnetic wave are the same thing. Light comes in many forms. This is something that science did not understand until recently. X-rays, visible light, radio waves are all the same thing. They just look different. We only see visible light, but we have learned to make tools that let us see other types of light. Jupiter seen at different wavelengths of light
Key concepts: EM spectrum Visible light –ROY G BIV Light is fast and travels straight Light acts like a Wave & Particle Reflection/Refraction/Diffusion Opaque/translucent/transparent Primary colors Wavelength/Frequency/Amplitude
Light also travels forever, and if its source is strong enough, we can see it.
The nearest star to our sun is Proxima Centauri It is 4.2 light-years distant in the constellation of Centaurus
Say hello to the super nova GRB 080319B, the brightest and most distant object we know of in the universe.
“Astronomers have placed the star in the constellation Boötes. They have estimated it to be 7.5 billion light years away from Earth, meaning the explosion took place when the universe was less than half its current age and before Earth formed.”
It is calculated to be 2.5 million times brighter than the brightest supernova ever recorded before it.
GRB 080319B is an example of how far light can travel and also of how vast the universe really is
Light has a strange combination of properties Light Acts Like a Wave It also acts like a stream of particles
Waves Key concepts –Wavelength –Amplitude –Frequency These words have the same meaning as in the study of sound.
Frequency = number of waves that pass a point in a certain time We usually measure it in Cycles per Second or Hertz (Hz)
Wave Terminology Wavelength - distance between two like points on the wave Amplitude - the height of the wave compared to undisturbed state Period - the amount of time required for one wavelength to pass Frequency - the number of waves passing in a given amount of time
Light has Certain Behaviors Reflection Refraction Diffraction
LIGHT can be REFLECTED - Reflection is light bouncing off of a smooth shiny surface.
Reflection is Light Bouncing off a shiny surface A B X Y Angle A = Angle B and Angle X = Angle Y Angle of Incidence Angle of Reflectance
Light Can Be Bent Refraction (or bending) of light happens when light passes through transparent materials of different density
“How Roy G. Bv Lost a Vowel The sequence of colors red, orange, yellow, green, blue, and violet may be remembered by memorizing the name of that fine fellow "ROY G. BV". This was originally "ROY G. BIV", because it used to be common to call the region between blue and violet "indigo". In modern usage, indigo is not usually distinguished as a separate color in the visible spectrum; thus Roy no longer has any vowels in his last name.”
Primary Colors of LIGHT not pigments Red Green Blue
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.
Understanding the EM Spectrum lets us See Thing in a Different Light.
The Sun at Different Wavelengths VisibleUltraviolet X-ray
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. Note there are 3 different frequencies.
Key concepts: Waves and particles EM spectrum Visible light –ROYGBIV Reflection/Refraction/Diffusion Opaque/translucent/transparent Primary colors Wavelength/Frequency/Amplitude