Electromagnetic Radiation!!
Electric Field to Magnetic Field
The Electric Field• Around every charge exists an Electric Field. Any other charge in the vicinity of that field
will move accordingly. https://phet.colorado.edu/sims/radiating-charge/radiating-charge_en.html
• When that charge begins to oscillate, it sends ripples through that electric field.
The Magnetic Field• Around every moving charge exists a magnetic field:
https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/magnetic-field-around-a-wire-i
• The magnetic field radiates outward perpendicular to the electric field
• When that charge seen in the Phet simulation or wire above oscillates back and forth, the magnetic field switches direction.
Electric Field Magnetic Field• Induction: A moving magnetic field creates an electric field (causes charges to move)
https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/electromagnetic-induction
• Alternating Current: Charges oscillate.—DC vs AC: https://javalab.org/en/dc_and_ac_en/
—Effect of AC on magnetic field: https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/magnetic-field-around-a-wire-i
• Transformer: – Transformer interactive: https://javalab.org/en/electric_transformer_en/
– Demo: https://www.youtube.com/watch?time_continue=181&v=AUO6N6VhXa4&feature=emb_logo
• CFL Beneath High Tension Power Lines: http://www.youtube.com/watch?v=cXhZvyGtMrk(3:05, 4:48)
Transformer
VpVs
DC or AC?
• Step up transformer
• Notice the number of coils!!
• Voltage and current vary but power remains constant!!
Electromagnetic Waves
An oscillating electric field• https://javalab.org/en/electromagnetic_wave_en/
• Sends ripples through the electric field
• creates an oscillating magnetic field
• Notice the magnetic field fluctuates perpendicular to the electric field
• The varying waves of magnetic and electric fields are known as Electromagnetic Waves!!
Light!!• These electromagnetic waves radiate outward from any oscillating charge!!
• Oscillating electric field produces an oscillating magnetic field which produces an oscillating electric field……
• The electromagnetic spectrum is waves ranging from radio waves to gamma rays!!
• Speed in a vacuum is 186000miles/s or 3x108m/s.
The Electromagnetic Spectrum
• Composed of oscillating magnetic and electric fields: https://ophysics.com/em3.html
• Can travel through a vacuum
• Speed in a vacuum is 186000miles/s or 3x108m/s.
• Visualizing the speed of light: https://www.visualcapitalist.com/visualizing-the-speed-of-light-fast-but-slow/
• No matter the frequency, you can NOT hear this type of wave!!!
• The spectrum: http://earthguide.ucsd.edu/eoc/special_topics/teach/sp_climate_change/p_emspectrum_interactive.html
Light!!
Wave or Particle?• Light exhibits traits of both wave and particle!!
• We will be studying the Wave Nature of Light
– Travels as a transverse wave
– Wave characteristics: frequency, period, wavelength, velocity
– Behave like sound waves: Interference, resonance, reflection, refraction, etc.
Notice the magnetic field and electric field oscillate at right angles to each other!!
Refraction• Light travels at 3 x 108m/s in a vacuum!!
• Light appears to slow down when entering other materials!!– Like running into ocean or lake… https://javalab.org/en/light_refraction_en/
• Fermat’s theorem of Least Time https://javalab.org/en/principle_of_least_time_en/
• Index of Refraction
• n dependent on frequency
n = 𝑐
𝑣
Where: c = speed of light in a vacuum = 3x108m/sv = speed of light in a mediumn = index of refraction (unitless)
• Rubbing a balloon on my hair– Charges balloon– Waving a charged balloon creates super low frequency radio waves!!
• Mentioned: The AC current throughout your house• Oscillating charge, oscillating with a frequency of 60Hz• Using the v = fλ equation, λ = 3100 miles!!
• Straws in a glass of water• Appear broken at waters edge• Appear larger on parts beneath water than on top
• Laser Light Box• Rectangle Prism: Refraction and thin film interference• Triangle Prism: Total Internal Reflection• Half Circle Prism: Refraction of lenses and total internal reflection
• Thin Film Interference Examples• Peacock feathers, bismuth, dichroic glass, rainbow paper
• Total Internal Reflection• Pink fiber optic plume• Fiber optic plastic tube plus laser shows laser zigzagging through tube.
Demos!!
Application
1. Things aren’t where they appear!!
2. Broken?
3. Mirageshttps://www.youtube.com/watch?v=AF43iwDWG9U
Mirage in China
Mirage!!
The sun at sunset might be below the horizon!!
Rainbows
Rainbow formation https://javalab.org/en/rainbow_by_raindrops_en/
Thin Film Interference At certain values of t waves 1 and 2 interfere constructively to produce a band of color
Great video!!https://www.youtube.com/watch?v=WTxDyYHaYAI
Total Internal Reflection
Index of Refraction
• Vacuum = 1
• Air = 1.0003
• Water = 1.33
• Window Glass = 1.52
• Diamond = 2.42
n = 𝑐
𝑣
Where: c = speed of light in a vacuum = 3x108m/sv = speed of light in a mediumn = index of refraction (unitless)
Demos!!• Transparent Beads disappear when water is added
• Crisco oil and glasshttps://www.youtube.com/watch?v=7hOZJL_bEPQ
Materials are categorized by index of refractionThe larger the index, the slower the light!!
So, What is Refraction?
n1sinθ1 = n2sinθ2
For air, n1=1
sinθ1
sinθ2
= n2
• As light passes from one medium to another, it bends!!https://phet.colorado.edu/sims/html/bending-light/latest/bending-light_en.html
Least Time
• Fermat’s Principle of Least Time 1630
• An explanation for why light refracts.
• Light does Not take the shortest distance!!
• Light takes the path of least time!!!
• Apparently nature tends to take least time as well!!https://puredhamma.net/quantum-mechanics-buddhism-buddha-dhamma/quantum-mechanics-a-new-interpretation/basis-of-proposed-interpretation-feynmans-technique-qed/exploring-possible-paths-fermats-principle-least-time/