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/