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49 Cards in this Set
- Front
- Back
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What are shadows useful for?
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used in xrays to see bones
used in art helpful for perception, provides lots of information |
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Point source of light provides??
What happens with large light source? |
point source produces sharp image.
larger light source --> blurred image created by umbra and penumbra |
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Lunar eclipse
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the shadow of the earth falls on the moon, blocking it from view.
sun --> earth --> moon total eclipse is in the umbra partial in penumbra |
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Solar eclipse
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when the shadow of the moon falls on the earth
sun-->moon--> earth total solar eclipse in umbra of moon partial eclipse in penumbra |
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Pinhole camera...what is it? how do you see the image? advantages/disadvantages?
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light proof box with tiny hole.
captures image on back of box image is upside down because light travels in straight lines through holes. so top of image on bottom of film. advantage: in focus disadvantage: not much light. |
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why not make pinhole camera hole bigger for more light?
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because if hole larger, light spreads out blurring image
small light source, focused image |
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Uses of reflection?
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radar for police, mirrors, telescopes, measure distance to moon
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law of reflection
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angle of incidence equals angle of reflection
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mirror reflections and human perception
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people assume light has travelled in straight line, percieving origin as behind mirror instead of off reflective surface . creating virtual image.
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Lateral inversion
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see things in reverse in mirror. right and left are switched
raise right hand in real life, images left hand raises. ambulance spelled backwards, when viewed in mirror is accurate two mirrors cancel each other. double reflection reverses lateral inversion |
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Diffuse reflection
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law of reflection holds. incidence = reflection
however, rough surface so rays will hit at surface at different angle due to different orientation, causing rays to scatter in different directions. dry road causes diffuse reflection vs wet road, specular |
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Specular reflection
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reflection off smooth surface. all angle of incidence and reflection are equal because hitting same level surface.
produces mirror like reflection |
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Convex mirrors
how are they used? |
push out, stretch image vertically
wide angle mirrors, used on cars. allow to see in peripherals but cause distortion "objects in mirror closer than they appear", messes with depth perception |
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Concave mirrors
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come in like cave, push image down vertically
focus light to focal point...often used in telescopes |
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Anamorphic art
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art that appears distorted when looked at with the naked eye. makes art and visible scene when viewed threw spherical mirror.
used in renassaince . hans holbein |
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Kinds of telescopes
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Reflective telescope - uses curved mirror to reflect light and create image
Refractive telescope - uses lenses to focus and present image |
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What telescope is better for scientists?
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Reflective because mirrors dont disperse light, no need for achromatic doublet.
also because lens needs to be held from bottom and blocks lens. mirror can be held from back |
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surface of telescope mirror?
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must be smooth, polished so roughness is less than wavelength
can smooth using mercury layer |
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Retro-reflection
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light reflected back towards its source with very little scattering
-dew drops: dew acts as lense, grass as screen. light goes through dew, bounces back off grass towards the eye. -reflective coating on shoes shines back at drivers, person looking with light |
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Refraction is...
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when light slows upon hitting a medium, aka water or glass
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refractive index
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n = speed in air/speed in medium = c/v
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Why does wave slow when entering a medium?
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because speed = wavelength x frequency.
when entering medium, frequency stays same but wavelength gets smaller so speed of wave gets slower. |
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artist who used refraction?
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damien hirst
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Relationship between n-value and refraction
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Increase in n creates increase in bend/refraction.
smaller n, less refraction....aka water refracts less than diamond. |
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Why do dense things have more refraction and bending?
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dense things like diamonds have more particles for the wave to wiggle through, so they slow waves down more.
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what is a mirage?
how does it form? |
-refraction in the atmosphere
-interaction between hot and cold air : hot and cold have different n value so light bends differently |
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what causes a mirage?
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hot air expands, so its charge expands changing its refractive index n. cold air n stays the same.
due to change in refractive index, light refracts creating a displaced image, or a mirage. because brain assumes light travels in straight line...we see mirage can happen backwards on ocean |
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What is total internal reflection?
what is the critical angle? |
when angle of incidence is larger than critical angle and all light is reflected back and doesn't go through the surface.
refractive index must be lower on other side of surface to occur when refracted light travels along surface |
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Fiber optics
uses? |
bent cable so light shined thorugh hits cable at angle greater than critical angle and goes through total internal reflection and none goes through the fiber and out.
carry information faster than electronic signal. medicine to view things inside body |
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Convex Lens
relationship between n and f? |
also known as converging lens
thicker in middle of lense goal to make parallel rays converge at focal point increase refractive index n creates more converging and a shorter f more curved lens = short f and more power |
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converging lens in water?
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creates f longer than in air, because waves move slower.
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what is focal length?
what happens to objects in focal length? |
distance from center of lens to focal point of rays ; 1/2 radius of sphere created by lens
object in focal length cant be focused, rays dont converge |
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what happens to images viewed through one lens? why?
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image through one converging lens is inverted
because P ray, M ray and F Ray. P-ray goes straight through lens then down to focal point, M ray through center of lense, and F-ray same as p-ray but through focal point on other side of lense drawing explains inversion |
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Concave lens
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diverging lens diverges rays. thinner in middle.
light spreads outwards. because brain assumes straight line, we think there is a focal point but there is not. |
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Compound lenses
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lens system featuring more than one lens
could be concave + concave, concave + convex, or any combo. |
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uses of compound lenses?
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zoom lenses: two converging lenses, changing distance between them allows changing focal length and zoom
achromatic doublet in photography, to focus different colors simultaneously |
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Chromatic abberation
and Achromatic doublets |
-different colors have differnet focuses through lenses, cant focus on red and blue at the same time
-solved by achromatic doublet. two lenses made from different glass. converging lense - crown glass, converges blue more than red diverging lens - flint glass, diverges blue more than red |
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types of distortion
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Pincushion distortion - squishes in towards middle
Barrel distortion - pushes out in middle |
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distortion by spherical abberation
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outer rays converge too much creating circle of confusion. steeper convergence at top of lense....two focal points!
solved by inserting stops and creating aperture. |
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stops and aperture
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stops by lens adjust aperture.
stopping down means shrinking aperture. stops located in MIDDLE of compound lens system small aperture = dim, focused large aperture = bright, fuzzier |
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What is dispersion
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when light is shined through a prism, light is refracted and disperses from white light to colors of rainbow.
disperses because colors have different wavelengths |
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Which is bent more in dispersion, violet or red?
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in dispersion, n depends on wavelength, so smaller wavelength violet will bend more than larger wavelength red.
LARGER N --> MORE REFRACTION violet slows and refracts most |
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Dispersion in diamonds
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highly dispersive - blue light refracts more than red.
shining white light into diamond spreads light a lot. each facet disperses and colors split, creating fire of diamond. |
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brilliance of diamond
flash of diamond |
light that reflects back out of diamond.
critical angle is small so more light sent out than normal glass moving diamond, how light changes and sparkles = flash |
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how is rainbow formed?
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back to sun, water in air.
raindrop acts as prism, refracting and dispersing light. colors reflect off back of drop and disperse more after exiting, creating rainbow you see. |
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how are double rainbows formed?
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light bouncing off inside of raindrop more than ounce. creates two reflections and two refractions so you see two rainbows.
because of double reflection, order of rainbow 2 is reversed. |
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Rayleigh scattering
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scattering of light off particles in atmosphere
reason why sky is blue. blue scatters most off particles due to smaller wavelength. long red wavelength doesnt scatter as much |
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why is sunset red?
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because light travels a long way through space. all blue light has scattered away higher in sky, leaving long wavelength red light which scatters lower and we can still see at sunset.
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why is a red sky good sign for weather?
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rain clears particles, less scattering at sunset, less red in sky.
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