Light Properties & Electromagnetic Spectrum PDF

Light is the only thing your eyes can actually see, all visual objects either emit light you can see with your eyes or reflect light that you can see with your eyes (emit light is lightbulb or sun, reflect is basically everything else) -​ Light is half particle, half wave- This is called the dua...

Light is the only thing your eyes can actually see, all visual objects either emit light you can see with your eyes or reflect light that you can see with your eyes (emit light is lightbulb or sun, reflect is basically everything else) -​ Light is half particle, half wave- This is called the dual nature of light -​ The particle theory is supported by the fact that light often moves in straight lines rather than spreading out (like laser beams), this is behaving like a particle (object) -​ Photoelectric Effect- When an electron gets knocked out of its orbit by a collision with a photon (more proof that light behaves like an object) -​ Waves don’t knock objects back, so the fact that light does this makes it clear that it behaves like a particle -​ Photon: -​ Massless bundle of concentrated electromagnetic energy, light is an electromagnetic wave Speed of light: 300 million m/s (3 x 108) -​ The speed of light in a vacuum is a universal constant -​ The distance light travels in one year is a called a light-year -​ This is a distance DON’T FORGET THAT -​ The letter “c” in a formula represents the speed of light Electromagnetic Spectrum in order of longest wavelength to shortest wavelength: This same order is from lowest frequency to highest frequency, also lowest energy to highest energy per photon -​ Radio waves -​ Used to encode information, safe and wickedly fast bc they’re EM waves -​ NOT A SOUND WAVE -​ Used for radio, TV, and telephones -​ Microwaves -​ Have same natural frequency as THE ELECTRONS of water molecules (when atoms have the same natural frequency as light, they absorb the light and turn it into heat, THIS IS WHY YOU CAN COOK FOODS IN MICROWAVES, YOU NEED WATER CUZ IT’LL PICK UP THE LIGHT, ELECTRONS WILL VIBRATE AND THE FOOD WILL HEAT UP -​ This is why you shouldn’t put metal, or anything without water for that matter, into a microwave—it won’t heat normally -​ Infrared -​ Kind of light that humans give off, use infrared goggles to see humans at night time -​ Also matches the nucleus frequency of water, so it can warm water as well (nucleus absorbs it) -​ Visible Light -​ Will talk about more soon -​ UV (Ultraviolet) rays  -​ Starting to get dangerous, high energy, give us sunburns, used to sanitize medical equipment bc it kills bacteria very easily -​ X-rays -​ Very high energy and dangerous, wear lead sheet over your body so you don’t get messed up -​ Go through muscles and skin and tendons and stuff, but not bones and teeth, why they’re helpful in showing broken feet and stuff -​ Gamma rays -​ Go through pretty much anything bc it’s super high energy, if it gets absorbed by a cell it usually kills it -​ We’ve learned to harness gamma rays in the form of the cyberknife -​ Cyberknife uses the superposition principle with Gamma Rays -​ Superposition Principle Review- Multiple waves can overlap in the same space, overlap will be either constructive interference or destructive interference (like parts overlap and make amplitude and intensity stronger OR unlike parts overlap and make amplitude and intensity smaller) -​ Cyberknife= laser that is a lot of weak gamma lasers that constructively crisscross at a single point -​ No cell can survive this, as a bunch of weak gamma rays have been put together and made 50-100 times stronger -​ This is how you operate on cancer, it gets killed immediately by a cyberknife Light is given off by electrons when they lose kinetic energy, on Earth basically only electrons do this cuz they’re free & protons aren’t -​ For lightbulbs & filaments, electrons bounce around with their kinetic energy for a while but eventually have to leave it, this emits light Lowest frequency of light a human can see if red, highest frequency a human can see is blue (violet) -​ Frequencies a little below red are infrared -​ Frequencies a little above blue (violet) are ultraviolet Transparent & Opaque materials: -​ Light goes through transparent materials -​ Light passes through materials whose atoms absorb the energy and immediately reemit it as light -​ If the light has a different frequency than the atoms it’s about to hit, that light will bounce off of the object, this is called opaque -​ If the light frequency matches the atom frequencies, that atom absorbs the light and turns it into heat, this is also opaque -​ If the frequency of the light is rly rly close to the atoms (close enough to fool the atom), so a little higher or a little lower  -​ The atom tries to absorb it but it’s not the right frequency, it gets spit right back out but now the light has already made it through the material -​ The frequency of the atoms is based on the vibrational frequency of either the electrons or the nucleus, either works -​ Glass and water are transparent to VISIBLE LIGHT, but not necessarily transparent to other types of EM waves -​ Glass is transparent to gamma waves as well, but not to UV light -​ UV Light creates resonance with glass, which is when the natural frequency of one object matches the natural frequency of another object, the one object will get the other object to start vibrating very strongly -​ When the frequencies match, resonance occurs and there’s a lot of vibrations, that’s where the heat comes from -​ Glass also absorbs infrared with its nucleus (matches nucleus frequency), while UV is absorbed by electrons (matches electron vibration frequency) -​ Whatever frequency of light hits glass is the same frequency as the light that comes out on the other side OPAQUE: -​ Objects can be opaque to some light but transparent to other EM waves (could not let visible light through but do let gamma through) -​ Metals are also opaque, when light strikes on metal surface and sets the electrons free (like microwaves striking metals and creating sparks), this is why metal is shiny -​ Clouds are only partly opaque to UV, so you can still get sunburned on a cloudy day Shadows- absence of light where an object blocks a light source from reaching that point: -​ Umbra is a sharp, well-defined shadow -​ Penumbra is a fuzzy, light distorted shadow -​ Lunar eclipse -​ Moon travels into the Earth’s shadow -​ Sun, Earth, moon, is the order of the objects -​ Solar eclipse -​ When the moon goes through the earth and the sun, Earth is in the shadow of the moon Polarization w/ light: -​ When all of light’s crests and troughs vibrate in the same plane, that light is polarized -​ Laser light is polarized light -​ Polarization is the process of making light have all of its crests and troughs vibrate n the same plane -​ Light waves are transverse btw -​ When light shines on a polarizing filter, only light that is polarized with the filter gets through (the filter absorbs all the other light) -​ Polarized sunglasses are polarized filters -​ They are designed to get rid of glare since 95% of glare is polarized horizontally but these sunglasses or polarized vertically  -​ When light bounces off of a shiny material, it bounces off it and polarizes parallel to the material, this is why most glare is horizontal Huygens’ Principle: -​ Light waves spreading out from a point source may be regarded as the overlapping of tiny secondary wavelets (a bunch of connected wavelets is a WAVEFRONT, and this looks like a circle), and that every point on any wave front may be regarded as a new point source of secondary waves -​ Godkin’s words: Imagine a firework going in all directions, a pulse of light is similar to that, it explodes out in all directions, after the original burst, each part on the little bulb of light is a new explosion and each point of each of those little explosions keeps bringing out new pulses, but these pulses are also weaker as there are more of them. -​ It’s why a source of light like a lightbulb fills a room, and how the sun’s light works Diffraction: -​ Definition: The spreading out of a wave when it passes through a narrow opening or past a sharp edge -​ How much it fans out depends on the size of the wave compared to the size of the obstruction that casts the shadow -​ When the opening is wide compared with the wavelength, the spreading effect is small, very little diffraction, casts a sharp umbra shadow (waves are small compared to the openings) -​ As the opening becomes narrower compared with the wavelength, the diffraction of the waves becomes more pronounced, casts a penumbra fuzzy shadow (waves are big compared to the openings) -​ Long wavelengths diffract better, cast fuzzier shadows -​ Diffraction grating has hundreds of narrow openings for light to squeeze through and it kinda forces light to diffract Interference: -​ Constructive, destructive, superposition principle -​ Superposition principle= Many waves can overlap and occupy the same exact space, applies to waves BUT NOT OBJECTS -​ Within an interference pattern, wave amplitudes may increase (constructive), decrease (destructive) or cancel out entirely (perfect destructive wow everything’s gone this is unlikely) Young’s Double-Slit experiment (involves interference & diffraction): -​ Demonstrated/proved the wave nature of light originally proposed by Huygens -​ Experiment shows constructive and destructive interference patterns that particles couldn’t mimic -​ Used monochromatic light for the double slit experiment -​ Monochromatic= single color -​ Passes light through two narrow openings onto a screen behind, there was a bunch of diffraction when this happened  -​ There were fringes- Bright and dark spots -​ Bright fringes show constructive interference, dark fringes show destructive interference -​ ALL OBJECTS have a part wave and part particle nature, more mass means it acts more like a particle (light doesn’t have mass which is why it’s so much more wave-like than normal particles) -​ We discovered this when we did the double-slit experiment with electrons and they ended up diffracting again -​ Waves still have same wavelength and frequency after double-slit experiment -​ Formulas for this experiment: -​ P.D. = (d)(y)/x -​ d= distance between two narrow slits in the experiment -​ x= distance between screen with two openings and screen with the fringes (the display screen) -​ y= distance from the center of any of the fringes to the center of the equilibrium line’s fringe (like the 0-point) -​ P.D. = (𝛌)(#) -​ P.D.= Path difference, more often than not, one beam of light will travel a further distance than the other, length of one path minus the length of another one (usually the equilibrium path) -​ 𝛌 is Lamda, it’s wavelength, measured in nanometers (10-9) -​ # tells you how many more wavelengths one beam of light went than the other -​ One of the waves traveled that many wavelengths further than the other -​ Each dark spot is a 0.5, each light spot is 1 full wavelength away from the middle -​ The dark spots happen bc crests and troughs cancel each other’s light out -​ Light spots happen bc the crests and crests overlap, since there’s a full period difference between the two Interference from thin films (like gas or bubbles): -​ They look rainbowy bc of a combination of constructive and destructive interference -​ When sunlight hits the bubble (white light), some of it bounces off of top surface, some bounces off the bottom surface, when they recombine, there’s a combination of constructive & destructive interference that creates a rainbow Laser light: -​ Monochromatic, coherent light -​ Light emitted by a common lamp is incoherent, there’s no organization to the crests and troughs! -​ Incoherent is totally random, but IT’S NOT A SYNONYM FOR OUT OF PHASE -​ Out of phase isn’t random, it’s when crests are with troughs and vice versa -​ Laser light is coherent bc all of the crests line up with each other and the troughs line up with each other -​ This is waves being in phase Colors: -​ You can change the appearance of objects by illuminating them with different colors -​ The color of an object depends on the color of the light that illuminates it (typically the color it is when illuminated by white light but could be different if the light on it is not white) -​ Color Spectrum: -​ ROYGBIV! -​ All of the colors of the rainbow combined turns into white light, and white light broken down turns into all of the colors of the rainbow -​ Sun gives off white light even tho it’s a “yellow star” -​ Something white reflects the whole ROYGBIV, none of it is absorbed, so you see full spectrum (appears white) -​ The colors that are being reflected are the ones you see (an orange would reflect orange and ABSORB the majority of the rest of the spectrum) -​ WHITE AND BLACK ARE NOT COLORS WHEN WE THINK OF LIGHT (white is a combination of ALL of the colors, and black is a LACK of any colors/light) -​ Black objects that you CAN SEE (pretty much all black objects you can see) absorb all colors of light that hit it, BUT THEY DON’T ABSORB EVERY SINGLE LIGHT BEAM, otherwise it would be invisible -​ If no light was reflected at all and all was absorbed, you wouldn’t see the object -​ Example: Vantablack is the blackest black, but it still technically reflects a TINY bit of light, but it basically looks like a void -​ Black lights are still TECHNICALLY reflecting colors—not enough to trigger your brain to see colors -​ The color of an opaque object is the color of the light it reflects  -​ The colors of objects around us are due to the way light reflects -​ Some objects give off the light, like lightbulbs, they are exceptions to this rule -​ All other colors have been absorbed and turned into heat -​ Different materials have different natural frequencies: -​ The frequency an object vibrates at naturally -​ Specifically based on the ELECTRONS’ natural frequency -​ Emitting radiation= Giving out electromagnetic waves -​ Resonance is when the frequency of one object matches the natural frequency of another object -​ When light has the same resonant frequency (natural frequency) as an object, that object will absorb the light and turn it into heat -​ If the frequencies aren’t close at all, the light will get reflected -​ If a material is transparent, then light will go through it -​ If it’s opaque, the light passes back into the medium from which it came. This is reflection -​ If a material absorbs light of most visible frequencies but reflects red, it’ll appear red -​ Most materials absorb light of some frequencies and reflect the rest -​ If a white square of paper were illuminated with exclusively blue light, the paper would appear blue -​ If there was a world illuminated by only blue light, everything would be either blue or black -​ In sunlight, a black square would be warmer than a white square bc it absorbs more light and turns it into heat -​ Because of how the human eye works, we break color light into three colors: -​ You have three different types of cells (called cones) in your eyes- They see red, blue, and green -​ Your brain is super smart and creates new colors when red, blue, and green are combined -​ L cells see red (Longest wavelength) -​ M cells see green (Medium wavelength) -​ S cells see blue (Smallest wavelength) -​ Petals of most yellow flowers, such as daffodils, reflect red and green -​ When our brain sees red and green light, our brain turns it into yellow -​ There is a certain range of frequencies -​ QUESTIONS ABOUT WHAT GETS REFLECTED AND WHAT GETS ABSORBED ALWAYS USE RGB, IGNORE ROYGBIV -​ Color of an object depends on the color of light being used to illuminate it -​ For example, green leaves in a room of red light are black -​ No colors are being reflected, they’re all being absorbed, bc the natural frequency of the leaves don’t match any of the frequencies of light in the room  -​ Dark vs light colors are based on how much light is coming to your eyes, if there’s only a little bit of blue -​ Transparent objects: -​ When an item absorbs specific colors, this is called selective absorption -​ Sunlight- Our sun gives off white light, but it’s considered a “yellow star” bc it gives off a little bit more yellow and green than any other color -​ Humans have therefore evolved to see yellow-green best -​ This is why tennis balls are yellow-green and firefighters wear that stuff, cuz it’s easiest for us to see -​ COLOR COMBOS FOR LIGHT: -​ You can make pretty much any conceivable color by overlapping red, green, and blue -​ Red green and blue makes white -​ Red and green makes yellow -​ Red and blue make magenta -​ Green and blue make cyan -​ 2 parts red and 1 part green makes orange -​ Mixing colors of light is called additive mixing -​ Lights are called additives -​ Red, green, and blue are called the additive primary colors -​ AKA mixing by addition -​ Mixing colors of pigments is called subtractive mixing -​ Pigments are called subtractives, subtract colors -​ Complementary colors: -​ Two colors that, when combined, create white light -​ Cyan and red are complementary -​ Magenta and green are complementary -​ Yellow and blue are complementary -​ Different way of asking for complement: What is white light minus (insert color) -​ Subtractives: -​ PIGMENTS/INKS YAY -​ When paints or dyes are mixed, the mixture absorbs all the frequencies each paint or dye absorbs -​ When red, green, and blue are mixed, everything is absorbed, meaning black is created -​ Paints and dyes contain particles of pigment that produce colors by absorbing light of certain frequencies and reflecting others -​ Red paint reflects red, absorbs blue and green, etc. -​ White dilutes the pigments, makes them less dark -​ Most efficient combination for full color spectrum is magenta, yellow, and cyan, like for printing CMYK woah -​ These are the subtractive primaries -​ Red pigment absorbs blue and green, reflects red -​ Green pigment absorbs blue and red, reflects green  -​ Blue pigment absorbs red and green, reflects blue -​ Yellow absorbs blue, reflects red and green -​ Cyan absorbs red, reflects green and blue -​ Magenta absorbs green, reflects red and blue -​ Why is the sky blue? -​ It (the atmosphere) scatters blue (high frequency) light, this is unique to Earth -​ Why are sunsets red? -​ There’s more red light at sunrise and sunset than green and blue by far -​ The atmosphere is much thicker at this time of day (cuz you’re further away from the sun, you only see it on the horizon) -​ Most of the blue light has scattered away -​ Red light has a long wavelength, it gets through easiest -​ Sunlights are orange bc some green gets through and stuff -​ Why is the ocean greenish-blue? -​ Bc the ocean slowly absorbs red light -​ You need 15-20 foot thickness water to totally lose all red light -​ Below here, a red swimsuit would look black Reflection & Mirrors: -​ Law of Reflection: Angle of incidence = Angle of reflection -​ These are ALWAYS equal -​ Normal line= A line drawn perpendicularly to a mirrored surface that allows you to measure reference angles (the angles of incidence and reflection) -​ Angle of incidence is the angle between the original beam of light and the normal line, angle of reflection is the angle between the reflected beam of light and and the normal line -​ Don’t use the angles the beams make with the mirror, these are only true on a FLAT MIRROR -​ How do flat mirrors work? -​ Half of your height of a mirror is all you need to see your full self in that mirror (a 6 ft person could see their full self in a 3 ft tall mirror) -​ Your brain takes a ton of visual info and makes a map of everything going on, it gets fooled when you’re in a mirror -​ Some animals are optically alluded too in the mirror and they attack -​ Virtual Image- Formed in your head as you look at a mirror, no two people can form the same virtual image bc you’ll be standing at different perspectives -​ Your brain thinks that you’re seeing something from the other side of a wall, 6 meters away (like your subconscious brain is thinking this even if you’re not thinking of this consciously) -​ Every mirror image, there’s a virtual image that you think the line of reflection actually kept going through the mirror, thai is what’s happening  -​ Being far away from a mirror doesn’t change how much of yourself you can see—it’s perspective based -​ If you can see your foot in a mirror, that means that it struck the mirror at an angle of incidence, and went back up to your eyes at the same angle of reflection (going halfway up to your head) -​ As long as -​ A person is standing 6 meters away from a mirror. How many meters away is their image? -​ 6 meters -​ The image of yourself is also the same height as you for flat mirrors Curved mirrors! Concave Mirrors: -​ When an object is facing a mirror, it’s facing like a mini cave of a mirror (it’s like the glass is pushed in, further away from the object) -​ There will be two points drawn in these questions on a line, the closer one is the focal point, and the further one is called the center of curvature -​ Sometimes only the focal point is drawn bc it’s more important -​ Center of curvature is always twice as far from the mirror than the focal point -​ Focal point: Where light that is parallel to the axis converges after striking the mirror -​ Beams of light that start parallel will bounce at a certain angle off the mirror and cross the focal point -​ Center of curvature- Would be center of the circle that the mirror would make if the concave mirror made a full circle -​ The distance from the mirror to the center of curvature would be radius -​ The side of the mirror that the object is on is called the light side, other side is called the dark side -​ Distances on the light side are considered positive numbers, distances on the dark side are considered negative numbers -​ Formula: (1/do) + (1/di) = (1/df) -​ do is distance from object to mirror -​ di is distance from the image to the mirror -​ df is distance from the focal point to the mirror -​ We want objects on the axis for this -​ We usually hold a lollipop with its end on the axis, the axis is a straight line protruding from the center of the mirror -​ You need to put film where the image is located to capture it -​ Magnification: m = (-di)/(do) -​ If this comes out as a negative number, then the image is upside down -​ When it’s upside down, that means the image is real -​ Not happening in your head, it’s actually happening -​ Being upright OR on the dark side means the image is virtual  -​ WHEN THE OBJECT IS CLOSER TO THE MIRROR THAN THE FOCAL POINT, IT’LL BE A VIRTUAL IMAGE, YOU CAN SEE THAT NO MATTER WHERE YOU ARE -​ WHEN THE OBJECT IS FURTHER FROM THE MIRROR THAN THE FOCAL POINT, IT’LL BE A REAL IMAGE, YOU HAVE TO FIND ITS LOCATION -​ For example, if the m is -½, then the image you see at that location is flipped upside down and ½ of the size Convex Mirrors: -​ When drawing lines, you need to make it LOOK like it came from the focal point -​ Reverse of concave -​ Can never make real images Index of refraction: -​ n= c/v -​ n is index of refraction -​ c is speed of light in a vacuum (300 million m/s) -​ v is speed of light in a new medium (something like water, glass, oil, or some other transparent material) (NOT a vacuum!) -​ Refraction= bending of a wave (changing direction) bc its speed changed -​ What makes a wave’s speed change? Entering a new medium does this -​ Light is fastest in vacuum, next fastest in gases, then liquids, then solids -​ Refraction is the bending/changing of direction of a wave due to its speed changing which was caused by a change in medium -​ MIRRORS CAUSE REFLECTIONS, NOT REFRACTIONS, SO THEY DON’T CAUSE CHANGES IN SPEED!!! Snell’s Law: -​ (n1)(sinΘ1) = (n2)(sinΘ2) -​ Index of refraction of first medium times the sine of its angle with the normal line is equal to index of refraction of second medium times the sine of its angle with the normal line -​ The index of refraction for air will always be 1 (very close so we just approximate) -​ For these problems, it will be light passing from one medium to another, it will make different angles with the normal line based on Diffraction: -​ When waves try to squeeze past a sharp edge or rly narrow opening, this makes the wave spread out, narrower opening makes it fan out more Lenses: -​ You look through lenses at objects, that’s how it works Double Concave:  -​ Looks like an hourglass, AKA Diverging Lens, makes light that is parallel to the axis DIVERGE away from a focal point -​ Double Concave bc it looks like it caves away from you -​ Also AKA Negative Lens, bc the focal distance is always negative for these lenses -​ They have two focal points, one on one side of the lens, one on the other -​ These two are symmetrical, the distances from the lens will be the same -​ First line in these problems diverges from first focal point -​ Second line in these problems diverges from the second focal point -​ Refraction is what’s making the light diverge from the focal points -​ Third line just goes straight through cuz there’s basically no angle You look through lenses at objects, that’s how it works Double Convex: -​ AKA Converging Lens AKA Positive Lens -​ The lines of light converge, the first line converges with the second focal point instead of the first one like the diverging lens -​ When you have the object further from the lens than the focal point, that’s how projectors work -​ When you have the object closer to the lens than the focal point, that functions as a magnifying glass When waves interact with matter, they can be reflected, transmitted, absorbed, or a combination of the three -​ Usually waves refract -​ If the wave is parallel to normal line/perpendicular to the surface, then it transmits through without any refraction -​ Refracted, is still going into same general direction but changing angle and speed -​ In refraction, waves make a larger angle with the normal line in the medium that they move faster in -​ They make a smaller angle with the normal line in the medium that they move slower in -​ Reflected, it bounces back, doesn’t change angle DOESN’T change speed -​ Doesn’t change frequency, crests become troughs & troughs become crests—it inverts itself Partial reflection- Some materials lets part of the waves through and bounces some of it back (glass is an example of this, reflects 4% of light off each of its surfaces) -​ Pane of glass has two surfaces, EACH ONE TAKES OFF 4% -​ Keep taking 4% of the new number (4% of the 96% of light) An object that is rigid to light bounces light back, for example silver reflects light very well -​ Glass and water aren’t as rigid to light The incident ray, the normal line, and the reflected ray, are all on the same geometric plane! The law of reflection applies to every single reflection, partial, totally, or anything else wow! Diffuse Reflection: -​ When light is headed towards a rough surface, it is reflected in many different directions -​ Everybody should be able to see these -​ In polished reflections, only some people can see the light reflected, since it bounces off at very specific angles -​ What makes a surface rough? -​ Rough= If the imperfection in the surface are larger than ⅛ the wavelength of the light -​ Since R G & B have different wavelengths, you could polish something to reflect red but not the other ones -​ If the imperfections in a surface smaller than ⅛ the wavelength of the light, the light will get reflected as a polished reflection -​ If they’re going in different directions, how are they still obeying the law of reflection? -​ Each different imperfection in the surface has a different normal line, so hitting in a kink in the surface would make it get reflected all wacky and stuff -​ Anything that EVERYBODY can see is diffuse Sound energy that isn’t reflected is either absorbed or transmitted through a medium -​ An echo is a reflected sound -​ More sound energy is reflected from a rigid and smooth surface than from a soft and irregular surface (why sound-insulating walls are always made of that fluffy stuff) -​ Soft irregular stuff will absorb the sound -​ When walls are too reflective, the sound becomes garbled bc of multiple reflections of sound waves called reverberations (like a bunch of echos all at once, it’s annoying af) -​ Both light and sound obey the same law of reflection -​ If you can see the person creating the sound in an auditorium→ you can hear them -​ If a light wave can travel through the space so can a sound wave -​ Refraction: Sound waves refract by bending towards the medium they move slower in/bending away from the medium they move faster in -​ Sound travels faster in hot air than it does in cold air -​ If you’re in a warm area, you may not hear a noise if there is a cold area near you, since the sound will bend towards the cold area Due to the refraction of light: -​ Swimming pools appear shallower -​ A pencil in a glass of water appears bent -​ The air above a hot stove or street seems to shiver -​ Stars twinkle Cool thing: Paths of refracted/reflected light are reversible If you can see something in a mirror, that thing can see you in a mirror Atmospheric refraction: -​ How mirages are formed  -​ Sometimes when the light at the top of the object angles down to SUPER HOT ground, when the light goes back up to your eye, we think it’s coming from the ground bc the light ray has curved and our brain looks straight ahead -​ This is why daytime is much longer than nighttime -​ It’s formed by real light and can be photographed, IT’S A REAL IMAGE!!! Dispersion: -​ The separation of the colors of light when the different colors refract at different angles while going through a medium -​ This can happen with glass or water -​ Rainbows in the sky are caused by light dispersion through water droplets Total Internal Reflection: -​ Occurs when the angle of incidence is larger than the critical angle -​ The critical angle is the angle of incidence at which the light is refracted at an angle of 90º with respect to the normal -​ If you have light underwater where the light is moving SLOWLY, it will have a smaller angle with the normal line than it will after it refracts and goes into the light -​ Different mediums have different critical angles- for example it’s 48º in water -​ If the incident angle is larger than the critical angle, the light never refracts, it only reflects off of the medium -​ When angle of incidence is AT the critical angle, total internal reflection still doesn’t happen Lenses ig: -​ Lenses change the directions that light travels -​ Causing refraction -​ Lenses do the most refracting to the light at its edges and the least to the light at its middle (cuz the lens itself is curved more at the edges) -​ Principal axis= The line joining the centers of curvature of lens of its surfaces -​ The horizontal line in Godkin’s diagrams -​ Beams of light parallel to the principal axis will converge at the focal point on a positive lens, or diverge on a negative lens -​ Focal Length= Distance from the center of the lens to the focal point -​ Lens create images by bending light -​ Converging lens is a magnifying glass when the object is close to it, but a projector when the object is far from it -​ Virtual images always upright for lenses, real images always upside down -​ When an object is far away from a magnifying glass, it gets projected as an upside down, real image -​ Double concave is used as the eyepiece in a camera, it takes a large plane of view and shrinks it down into a small window of view -​ AKA negative lenses, they ALWAYS show shrinking The Human Eye: -​ The pupil is the opening that lets light into the eye -​ The optic nerve connects your brain to your eye (it makes a blind spot in your eye) -​ The cells inside the eye: -​ Rods- look like little cylinders, these are all over the retina -​ They see black and white, they work in both dim and strong light, excellent at seeing peripheral motion -​ Cones- see color -​ L (long) cones see red, M (medium) cones see green, S cones see blue (short) -​ These are located in a special patch called the fovea -​ Need significant light, don’t work in dim light -​ Retina= the inner lining of the eye Lenses have natural imperfections: -​ Imperfections= Aberrations -​ Chromatic Aberration: -​ When the different colors of light disperse slightly in the glass, like they do in a prism -​ Only solution for this is to make the lens as thin as possible to reduce the dispersion, but it’s not possible to totally get rid of it -​ Spherical Aberration: -​ Occurs because the edges of the lenses cannot focus the light as well as the middle of the lenses can focus it -​ Solution: Cover the edges