Light Basics and Geometrical Optics
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This text is meant to accompany class discussions. It is not everything there is to know about uniform circular motion. It is meant as a  prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations. See the links below.
 
Light Behaviours

 

When light hits a surface it will do one of 6 things.

These behaviors can be explained by examining the particle properties or the wave properties of light.

 

When a charge ACCELERATES it creates a magnet field. When the magnet field is created an electric field is created perpendicular to the magnetic field. The Electric and magnetic field look like the ones shown below.

(Image by SuperManu (Self, based on Image:Onde electromagnetique.png) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY-SA 2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], via Wikimedia Commons)

This is an application of the open palm right hand rule where the electric field is the thumb, the magnetic field are the fingers the the palm is the force pushing the wave along in the velocity's direction.

These two waves are actually one wave called an electromagnetic wave. This also referred to as electromagnetic radiation. You probably refer to electromagnetic waves as "light." All of the wireless devices in your house produce light. We can't detect their frequencies, (or colors,) with our eyes. Instead we have to use devices like, phones, radios or blue tooth receivers to "see" their colors. Infrared remotes use a frequency of red light that we can't detect with out help. How every you smart phone can see them.

 

Activity to do with your smart phone
Set your smart phone up or any digital camera to take a video. Find a TV remote, they are usually infrared remotes. Point the remote at the camera lens while pointing pressing the power button on the remote. In the camera's image screen you will see a white light. This light is the camera converting the infrared, "color," to white. Take a moment and try it. The remote sends a signals to the television as a series of blinks. These blinks are too fast for use to see in the camera. But if your camera has a high speed mode, it might be able to see the blinking light on the remote. (This does not work on newer iPhones, iPhone 9, iPhoneX.")

 

There two ways of observing an accelerating charge.

(1) Change direction. A charge the moves perpendicular to a magnetic field curves. This is a change in direction.

(2) A charge that changes speed.

The positive charge above is traveling across two boxes, "A" and "B." Which box will emit a wave of electromagnetic radiation?

 

Law of Reflection

A specular reflection occurs off of a smooth surface. One light ray is incident on the surface and one leaves the surface at the same angle. This is called the law of reflection. It only applies to smooth surfaces.

When describing light rays, all angles are referenced from the normal line to the surface at the point of incidence to the light ray.

Here's Something Interesting Using Reflection...

This an image of a reflection in a large, calm, lake. Notice anything peculiar about the image above? I posted it upside down. Click here to see the image right-side up.
Image credit: Jeff , https://www.flickr.com/photos/jeff_sch/11190097303/ site: https://www.flickr.com/photos/jeff_sch/ accessed April 9, 2017.

 

Waves

 

 

  • λ = the wavelength measured in meters [m.] "λ" is pronounced lam-da
  • A = amplitude measured in meters [m.]
  • c = the wave's speed. For light in a vaccuum, "c" is 3.00 x 108 m/s. For sound at STP conditions in the atmosphere, it is 343 m/s, (767 mph.)
  • f = the frequency of the wave measured in Hertz [Hz]. A Hertz is 1/s. for visible light, think of the frequency as the color of the light.

The wave equation

c = λf

This equation provides a way to switch between wavelength and frequency. (A common calculation.)

The energy of a single photon is

Ephoton = hf

h = 6.626 × 10-34 J/s. This is called Planck's constant. Do NOT memorize it.


Most waves need something to travel through because they rely on the motion of particles to carry the wave. 20 years after teh end of the civil war, it was believed that light, electromagnetic waves, must also uses a medium to travel. This medium was called the "ether." If this is true then we are also moving through the ether. This means that the speed of light will vary depending on the direction you are pointing if you measure the time it takes for an electromagnetic wave to trave from location "a" to location "b." In 1887 Albert Michelson and Edward Morley conducted an experiment to test this theory. They got an unexpected result. Their experiment showed the speed of light to be the same in every direction. We now know that electromagnetic waves are made from the interaction between an electric field and a magnetic field. Because of this, electromagnetic waves do not travel through anything. This is why light from the Sun can travel through the vacuum of space while sound does not.

Click the image below.

Did you hear that? No? That's because you shouldn't hear anything in the vacuum of space. So often in science fiction television shows and movies you can hear the sounds of ships exploding and engines burning when the scene is shot from outer space. On the 2004-2009 television series BattleStar Galactica, the writers and directors got it right. During the scenes that are presented from the perspective of outer space, like the one above, no sound should be heard. Even when there are explosions on the ships. Remember this the next time you are a movie that takes place in outer space.

(Image source: http://www.battlestargalactica.us/community/application/widgets/illuminantgallery/externals/images/02.png from, www.battlestargalactica.com, accessed on April 7, 2017.)

 

The Light Spectrum

 

What we consider to be light is usually the part that we can see. "Light" is actually much bigger than this. Visible light is a sall part of the electromagnetic spectrum. Radio signals, microwave ovens, x-ray machines all emit light we cannot "see."

image: http://www.artinaid.com/wp-content/uploads/2013/04/Light-Spectrum.png accessed 02/15/2016

"radio" waves LOWEST Energy

This video can be found on YouTube at https://youtu.be/QNzb3ywQ3Q8

Microwaves

This video can be found on YouTube at https://youtu.be/ShHUCiKAPWQ

Infrared (IR)

This video can be found on YouTube at https://youtu.be/wrlALgesniA

Visible Light

This video can be found on YouTube at https://youtu.be/3fTDKmeU65U

UV

This video can be found on YouTube at https://youtu.be/bDj8xFizduU

X-Rays

This video can be found on YouTube at https://youtu.be/EWfZCd_A6ZI

 

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by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)