Invisibility for Muggles!
-
Upload
laserclassroom -
Category
Education
-
view
213 -
download
4
Transcript of Invisibility for Muggles!
Exploring the basics of the Rochester Cloak
with an Invisibility Kit by
Making Invisibility VISIBLE
– for Muggles
Harry’s Cloak• Light weight and portable
• Full coverage of a human sized object from any angle
• Allows you to see the background clearly
• Relies on the unique optical properties found in the fur of DemiGods
• Not for Muggles • YET?
Romulan Space Ships• Free floating
• Full coverage of a space ship sized object from any angle
• Allows you to see “right through it” into outer space without distortion
• Relies on the unique optical properties found in something the Romulans will kill you over before they give it to you
• Not for Earthlings • YET?
Invisibility in the classroom• Engaging, enticing, exciting!!
• Easy to demonstrate: portable, affordable, do-able at the high school (middle school?) level
• Draws on or puts to use topics, formulas, ideas, skills and practices we know we need to teach
Invisibility is a function of light• Visible
• Enough visible light (400-700nm) from a source bounces off an object and into our eyes to be detected.
• Invisible • Not enough light (too small… too far away) • Light not in the visible spectrum (IR, UV)• Does not bounce off the object and into our eyes
• Blocked (absorbed) • Bent (refracted)
Light is an Electromagnetic Wave
What can control both the electric and magnetic fields?
The Electromagnetic Spectrum
What can control light in the visible range?
Refraction• Light changes speed as it travels from one media to
another (air to glass for example)
• Light always bends towards the denser medium (normal)
# 1: Index of Refraction
• 1 – fill with water, no difference in index of refraction• 2 – pyrex and oil have the same index of refraction• Benefits: inexpensive, easy, portable, demonstratable• Limitations: liquid, colorless
# 2: Metamaterials- Nano Structures
• Nano sized human made molecular arrangements that suppress scattered light waves
• Break the laws of Physics!! Reverse Snell’s Law
Limitations of Meta Materials• Very, very expensive to
produce or demonstrate• Very, very small • Neither portable nor
invisible• Many do not work in the
visible range – Stealth, Radar
• You cant see out!
Rochester Cloak• First 3D visible light
invisibility cloak• Developed at the
University of Rochester in NY
• Creates “regions of invisibility” that can completely hide objects.
• Uses refraction through a conventional 4 lens system.
Rochester Cloak• Hides real objects
from several angels• Allows the background
to be seen clearly• Portable and EASY to
demonstrate• Inexpensive• Paraxial Ray Optics
Cloaking – Linear Algebra
• but… Let’s start at the beginning..
What it does• As light reflects off of the background, it refracts as it
passes through the lenses creating “cloaked regions”.• When an object is placed inside of a cloaked region, light
from the background passes around object causing the background to be visible, rather than the object!
Refraction with Lenses: Convex• Lenses redirect light• Convex lenses are thicker in the middle and thinner at
the edges• This shape causes rays to bend towards the center of
the lens.
Refraction with Lenses: Concave• Lenses redirect light• Concave lenses are thinner in the middle and thicker at
the edges• This shape causes rays to bend towards the center of
the lens.
Focal Length/Point- Predictable!!!• All rays meet at a point called the
FOCAL POINT• The distance from the lens to the
focal point is called the FOCAL LENGTH
• The Focal Length is predictable• Critical info for understanding
Image formation
Rochester Cloak: • Cloak depends on the spacing between the lenses
• Distance between first two lenses• Parallel rays are refracted to focal point by lens 1• Resultant rays source at exactly f2 from lens 2• So… rays emerge parallel from lens 2
Optics Matricies: Linear Algebra
Smith Matricies
Rochester Cloak Setup
• Two pairs of convex lenses• Pairs having focal lengths f1 and f2
• F1 focal length is (150mm)• F2 focal length is (50mm)• Set up in straight line
• f2 lenses in middle, f1 on outside• distance between f1 and f2 lenses
on ends• d1=d3=f1+f2
• distance between f2 lenses in middle
• d2=2f2(f1+f2)(f1-f2)
Build your own cloak: Set up1. Place lenses in lens holders. Keep track of focal lengths.
TIP: thicker lens has shorter focal length.2. Stick graph paper to wall at end of long surface.3. Place one f1 lens at zero mark.4. Place one f2 lens 200mm from first lens. TIP: measure
from surface of the lenses, not centers!5. Place other f2 lens 200mm from second lens. Again,
measure from the surface!6. Lastly, place remaining f1 lens 200mm from third lens.
Build your own cloak: testing1. Use a LASER pointer to check that lenses are
aligned:1. Shine LASER through centre of first lens towards graph
paper.2. Beam should emerge through all four lenses unchanged:
no bigger or blurrier.• Stand sevral inches from first lens.
• Crouch to be on eye-level with lenses.• You should see the graph paper unmagnified through the
lenses.• Have someone move a pen or other long, thin object
between lenses 2 and 3. Object should disappear towards top and bottom of lenses.
Kits and FREE Lessons
www.laserclassroom.com