OPTICS Notes PDF

OPTICS UNIT SUMMARY INTRO TO LIGHT BASICS OF LIGHT - Light travels extremely fast, as a dark room immediately fills with light when a lightswitch is turned - Light travels so fast that something traveling at the speed of light could circle the earth’s equator could...

OPTICS UNIT SUMMARY INTRO TO LIGHT BASICS OF LIGHT - Light travels extremely fast, as a dark room immediately fills with light when a lightswitch is turned - Light travels so fast that something traveling at the speed of light could circle the earth’s equator could travel 7.5 times in one second - Light travels in a straight line - A flashlight in a dark room will shine in a straight line PRODUCTION OF LIGHT - note that we can only see light bc of light entering our eyes Two kinds of light sources 1. Luminous source: producing its own light - ex. Flashlight, flame 2. Non-luminous source: does not produce light, can only be seen using reflected light - ex. Textbook, chalkboard, pencil Different light sources Name Description Example(s) Incandescent - Light produced by heating a material until it glows - Incandescent light bulbs: filament - When object becomes hot enough it emits light inside is heated until it glows Electric Discharge - Light produced when an electric current passes - Neon signs: electric current passes through a gas or vapor through neon gas within sign to grow diff colours Phosphorescence - Light emitted by a substance after it has absorbed - glow in the dark stickers: glow and light or other radiation continue to glow in the dark after - Continue to glow after external light source cuts being exposed to light Fluorescence - Light emitted by a substance when it absorbs light at - one wavelength (ultraviolet) and then it emits almost immediately as light (longer wavelength) Chemiluminescence - Light produced by a chemical reaction without the - Glow sticks: when the capsule need for heat breaks, the chemicals inside mix, producing a chem reaction and light Bioluminescence - Light produced by living organisms through a - Fireflies chemical reaction in their bodies - Found in nature Triboluminescence - Light produced when a material is mechanically - Quartz crystals: when rubbed or disturbed—crushed, rubbed, or scratched fractured, they can emit a brief - occurs due to the breaking of chemical bonds or the flash of light separation of electric charges in the material  OPTICS UNIT SUMMARY Light-Emitting - semiconductor device emitting light when current - LED lights (literally stands for Diode flows through it LED) - Unlike traditional light bulbs that rely on heating a filament, LEDs produce light through the process of electroluminescence, where energy is released in the form of light when electrons recombine with holes in the semiconductor material Radiation: method of energy transfer that doesn’t require a medium (vessel), energy travels at the speed of light Electromagnetic wave: a wave with both electric and magnetic parts, doesn’t require a medium and travels at the speed of light Light as an electromagnetic wave - Light energy is transferred through radiation - Under certain conditions, light shows wave-like properties Light as a particle - Travels as a particle called a photon - Lasers with different colours react differently to different materials BASICALLY light is always a particle but can travel as a wave or in a line. As a particle: In interactions like the photoelectric effect and scattering. As a wave: when moving continuously, passing through air or water In a straight line: In uniform media or free space, where there are no obstructions or changes in the medium. Understanding light as a wave - Transverse wave, alternating electric and magnetic fields - Does not need a medium to occur - Trough: bottom, crest: peak, amplitude: measure of the middle, Electromagnetic spectrum: the classification of electromagnetic waves Visible light: electromagnetic waves that human eyes can detect  OPTICS UNIT SUMMARY Left to right - lowest, longest wavelengths to stronger, shorter wavelengths COLOURS ASSOCIATED WITH VISIBLE LIGHT - White visible light composed of continuous sequence of colours that can be seen by the human eye (the rainbow) - All seen colours are associated with a wavelength and frequency, with wavelengths ranging from 400-700 - A prism can be used to separate sunlight or white light into the colours of a rainbow, called the visible spectrum - Shorter wavelength = greater energy - Explains why UV light is more damaging to eyes than visible or infrared regions of the spectrum - Isaac Newton showed that a triangular prism slows down the speed of light; the colours are slowed down to different degrees which is why this causes the colours to be separated into different colours  OPTICS UNIT SUMMARY - Newton was the first scientist to state that there were 7 distinct colours that are visible in white light LASERS - Different from other forms of light because it produces electromagnetic waves of exactly the same waves and energy levels, resulting in a very pure colour - Light-sensitive cells in the retina become overloaded PROPERTIES OF PLANE MIRRORS To summarize, there are three models of light: as a photon, as a wave, as a straight line COLOURS OF OBJECTS - the interaction of objects with light - Objects can either reflect or absorb colours on the spectrum (ROYGBIV) - If an object looks red or orange, it’s because the it absorbed all the colours except red/orange, therefore reflecting - Objects appear black when all light is absorbed and none is reflected, while objects appearing white reflect all the colours - The night sky is black bc there’s no light to be observed Leaves on a tree use blue and red light to carry out photosynthesis. The colored light is absorbed by the tree and made into energy. Because green light is not used, the leaves appear green. MIRRORS - objects that reflect all light and absorb none - Front of a mirror is usually a sheet of glass, the back is a thin reflective layer (aluminum or silver) TERMS Image - reproduction of an object through the use of light Reflection - The bouncing back of light from a surface Plane - flat Incident Ray - incoming ray that strikes a surface Reflected Ray - ray that bounces off a reflective surface Normal - perpendicular (at an angle of 90° to another line or surface) line to a mirror surface  OPTICS UNIT SUMMARY Angle of Incidence - angle between the incident ray and the normal Angle of Reflection - angle between the reflected ray and the normal Ray diagram - a theoretical tool that shows how light travels from one place to another, including how it interacts with objects LAWS OF REFLECTION 1. The angle of incidence will always equal the angle of reflection. 2. In ray diagrams, the incidence ray, reflection ray and the normal lie in the same plane. Symbol is a sign for angle Spectacular reflection: reflection of light off a smooth surface - Causes a clear image to be formed because all angles of reflection are the same - Eg. a mirror Diffuse reflection: reflection of light off an irregular or dull surface - Causes a blurry image because the angles of reflection are not the same - Eg. a painted wall - RAY DIAGRAM FROM A STRAIGHT ANGLE  OPTICS UNIT SUMMARY RAY DIAGRAM FROM A DIFFERENT ANGLE DRAWING A RAY DIAGRAM WHERE ALL ANGLES ARE PUT TOGETHER OPTICS UNIT SUMMARY  OPTICS UNIT SUMMARY For an image to form, two incident and two reflection rays are needed CHARACTERISTICS DESCRIBING AN IMAGE Size: same size, larger than, smaller than the object Attitude: upright or inverted Location: closer than, farther than, or in the same distance as the object Type: real or virtual image REAL VS VIRTUAL IMAGE Virtual image: no real light is available to the image, our eyes project the light rays behind the image (virtual rays intersect) - Creates a perception of an image, represented by a dotted line - Reflection in a mirror Real image: when light rays converge or meet at a destination CONCAVE AND CONVEX MIRRORS Concave mirror: reflective surface curves inwards eg. a spoon How objects will appear in a concave mirror: - If an object is close, the mirror will make the object appear larger and upright. - If object is farther away, mirror will make object appear smaller and inverted Convex mirror: extends outwards eg. the back of a spoon, gas station mirrors CURVED MIRRORS - RAY DIAGRAMS  OPTICS UNIT SUMMARY Centre of curvature: centre of the sphere Focal point: point of convergence for all incident rays when reflected off the mirror surface Vertex: point where principal axis intercepts mirror Principal axis: line going through C and the centre of the mirror Object: location, direction and height of the actual object from the mirror Image: reflection of the object CONCAVE MIRRORS - When object is between the focal point and the vertex, an upright virtual image is produced - When object is anywhere after the focal point, an inverted image is produced RAY TYPES FOR CONCAVE MIRRORS - at least 2 to form image 1. An incident ray travelling parallel to the principal axis will reflect back through the focal point 2. Incident ray travelling through the focal point will reflect back parallel to the axis 3. Incident ray travelling through the centre of curvature will reflect back on itself (normal to the mirror)  OPTICS UNIT SUMMARY concave mirror image An object on the focal point would not be able to form an image because reflected rays do not intersect An object between focal point and vertex does form an image KEY IDEAS - You NEED TWO reflected rays to intersect to get a image - If an object is placed between the focal point and the vertex it will produce a upright virtual image - An object placed on the the focal point will never produce a image - An object placed anywhere after the focal point will always create an inverted image - If the reflected rays meet before the mirror its a real image, if they meet beyond the mirror it’s a virtual image  OPTICS UNIT SUMMARY CONVEX MIRRORS - reflecting surface curves outwards Images are predictable - ALWAYS smaller, upright, closer, virtual - Images distort at the edges F and C are behind mirror in convex diagrams, unlike concave diagrams - A convex mirror always producing a virtual image makes sense given that our F and C are behind the mirror (remember any image produced behind the mirror is always virtual) RAY DIAGRAMS FOR CONVEX MIRRORS - One incident ray needs to be parallel to principal axis and reflects through focal point (be sure to add virtual extensions) - The other incident ray goes through the focal point and reflects parallel to the principal axis (be sure to add virtual extensions) - Where reflected rays meet is location of image  OPTICS UNIT SUMMARY REFRACTION Refraction: The bending or change in direction of light when it travels from one medium into another Medium: material that moves energy or light from one substance to another, or from one location to another CAUSE OF REFRACTION - Light’s travel speed: 3.00 × 10⁸ m/s in a vacuum, 2.26 × 10⁸ m/s in water, 1.76 × 10⁸ m/s in acrylic -> depending on the medium light is travelling through, it moves at different speeds Vacuum: a place (to the highest degree possible) that is without matter, including air Eg. a thermos: a bottle with a double-walled container inside. Air between the walls is sucked out during construction, creating a vacuum. This keeps substances hot/cold RULES FOR REFRACTION 1. The incident ray, refracted ray, and normal line all lie in the same plane. Incident ray and reflected ray are on opposite sides of the line that separates the two media. 2. Light bends towards the normal when light slows down in the second medium. Light bends away from the normal when light is faster in the second medium. Partial refraction: when some light passes through a boundary between two materials and changes direction, while some of the light bounces back into the first material - Accompanied by reflection (some light is refracted, some is reflected)  OPTICS UNIT SUMMARY - Jean Foucalt (French physicist) concluded that the speed of light (v) is always less than the speed of light in a vacuum © Refractive index: the ratio of the speed of light in a vacuum to the speed of light of the medium SNELL’S LAW - Describes the relationship between the angles of incidence and refraction - n1 = incident index ; n2 = refractive index INDEX OF REFRACTION  OPTICS UNIT SUMMARY LENS LENSES VS. MIRRORS - Mirror: an object that absorbs no light and reflects all light - Lens: a transparent object with at least one curved side that causes light to refract Axis of Symmetry (AoS): imaginary vertical line drawn through optical centre of lens Refracted ray: light ray that leaves the lens after refraction and goes back into the air In lenses, light is refracted at the first air to glass surface. Light then travels through the glass of the lens and is refracted again at the glass to the air surface on the other side. We are ONLY concerned with the direction of the incident ray entering the lens and the refracted ray exiting the lens. LENS AND KEY POINTS Optical centre (O): the exact point in the centre of the lens horizontally and vertically Principal focus (F): light rays that are parallel to the principal axis converge - Light can come from from either side of the lens, so there is a secondary focus (F’), which is the same distance from the lens as the first focus CONVERGING AND DIVERGING LENSES TYPES OF LENSES 1. Converging - convex lens - Thicker in the middle, thinner at the ends - Bring parallel rays towards a common point after refraction through the lens EXAMPLES Far-sighted glasses - Converging lens produces an image farther from the eye than the object so things can be seen clearly Magnifying glass - Focuses light rays to a magnified virtual image of an object  OPTICS UNIT SUMMARY - Object is placed close to lens, at a distance less than the focal length, magnifying object Focal points of lens Focal length: distance between focal point and the vertical axis 1. A ray parallel to the PA will refract through the lens and pass through F on the opposite side of the object. 2. A ray that passes through the secondary principal focus F’, on the same side of the object will refract parallel to PA. 3. A ray passing through the centre of the lens will not refract & continue in the same direction COMPLETED CONVERGING LENS DIAGRAM IMAGE PROPERTIES OF CONVERGING LENS Diverging lenses: concave lens - Thinner in the middle, thick along the edges - Parallel ray diverge after refraction from the lens  OPTICS UNIT SUMMARY - Light rays parallel to the principal of axis in diverging lens do not converge, rather they spread apart - If you project these diverging rays backwards it looks like it comes from a virtual focus. This point is now referred to as the principal focus (F). The secondary principal of focus (F’) is now on the other side of the lens, where the rays actually diverge EXAMPLES Binoculars Near-sighted glasses - Requiring diverging lens that compensated for overconvergence of the eye Door peephole - Uses a diverging lens to create a wide-angle view of the outside of the door RULES FOR RAY DIAGRAMS 1. A ray parallel to the PA, will diverge from the lens as though it was coming from the principal focal point. Note that we are drawing virtual extensions through the focal point. And extending that is our real refracted ray 2. A ray passing through the centre of the lens will not refract & continue in the same direction 3. A ray through the secondary principal of focus F’, on the opposite side of the object, that refracts parallel to PA. COMPLETE RAY DIAGRAM FOR DIVERGING LENS  OPTICS UNIT SUMMARY LENS EQUATIONS - One way to figure out how lens images form is ray diagrams, another is equations LENS TERMINOLOGY - do= distance from the object to the optical center - di= distance from the image to the optical center - ho= height of the object - hi= height of the image - f = focal length of the lens; distance from the optical center to the principal focus (F) THIN LENS EQUATION - equation relating f, do, and di 1/do + 1/di = 1/f 1. Object distances are always positive 2. Image distances are positive for real images (when the image is on the opposite side of the lens from the object) and negative for virtual images (image is on the same side of the lens as the object) 3. The focal length (f) is positive for converging lenses and negative for diverging lenses Variable Positive Negative Object distance Always Never (do) Image distance Real image Virtual image (di) (opposite side (image is on the of the lens as same side of the object) lens as the object) Height of object When When measured (ho) measured downward upward Height of image When When measured (hi) measured downward upward Focal length (f) Converging Diverging lens lens Magnification Upright image Inverted image (M)  OPTICS UNIT SUMMARY MAGNIFICATION EQUATION - used to determine the size of the image in relation to the size of the object M = hi/ho = -di/do 1. Object (ho) and image (hi) heights are positive when measured upward from the principal axis and negative when measured downward 2. Magnification (M) is positive for an upright image and negative for an inverted image THE HUMAN EYE - An optical instrument that allows us to see the world - The eye is shaped as a converging lens (causes light to converge) COMPONENTS OF THE HUMAN EYE Component Function and explanation name Iris - the coloured Controls how much light is let into the eyes, done by relaxing and part of the eyes constricting, change based on surrounding light - Low light = open up to let in more light - Bright light = constrict to let in less light Cornea - For focusing light - light refracts through cornea by bending as it transparent bulb passes through transparent layer on top of pupil - Cornea is a protective layer Pupil - hole in the Where light enters the eyes, located between cornea and lens of the middle of the iris eye Lens - focusing Focuses light into the retina and allows for things to be seen clearly light into retina Lens are converging, will converge into the retina - Always producing a smaller, inverted, real image  OPTICS UNIT SUMMARY Retina - light Phototransduction: process of retina converting light signals into an sensitive cells electric signal that is transmitted to the brain through the optic located in the nerve back of the eye 1. Light hits retina 2. Photoreceptors convert light into electric signals Photoreceptors: 3. Electric signal transmitted to brain w/ optic nerve light detecting Retina Components cells Rods - 120 million rods that can see black, white and shades of gray, also allow us to see shapes - Sees brightness level: rods are working when it is dark and you can’t see Cones - 7 million cones allowing us to see colour - Three types of cones allowing us to see bright light: red, blue, green sensing cones - Colour blindness is due to a deficiency in one of their cones - Rods and cones send gathered info to optic nerve, then transmitted into electrical signals, allowing brain to put together a picture Optic nerve - Place where optic nerve never lies creates a blind spot in the back sends visual info of your eye bc there are no light sensitive cells (it’s a small area) from retina to - Brain can not see if image is projected into this spot brain - Blind spot goes unnoticed bc each eye compensates for the blind spot in the other eye Sclera - white Very tough, covering majority of the eye part of eyes Tiny blood vessels within sclera, rubbing eyes can cause vessels to break, which makes them red TYPES OF VISION - Differences in vision is related to eyeball size or effectiveness of lens Normal vision: lens focuses directly onto retina Nearsighted vision: lens focuses light in front of retina Farsighted vision: lens focuses light behind retina Solution: laser eye surgery, glasses, or contact lenses  OPTICS UNIT SUMMARY EYES AS INSTRUMENTS - We do not see with our eyes: eyes gather light + info, allowing brains to form pictures - Cornea-lens combination of the eye acts like a converging lens and produce smaller, real, inverted image on the retina - The brain flips image so it appears as upright EYES ACCOMMODATION - Ciliary muscles (eye muscles) help the eye focus on distant and nearby objects by slightly changing the shape of the eye lens - The muscles do this by slightly contracting or relaxing to change the distance - Change in shape leads to change in focal length of lens, allowing image focusing to happen in the retina - This is called accommodation!! - Healthy eyes can easily accommodate, other eyes may not be able to focus as well, resulting in blurred vision Hyperopia: far-sightedness - The inability of the eye to focus light on near objects: no difficulty seeing things from a distance, difficulty seeing things up close - Causes: when the distance between the lens and retina is too small or cornea-lens combination is too weak - All light focuses behind the retina - Needs help with refracting light so it requires a converging lens - The actual lens shape is modified from the basic converging lens and is called a positive meniscus. A positive meniscus is still a converging lens because the middle part of the lens is still thicker than the edge.  OPTICS UNIT SUMMARY - ’ Presbyopia: age-related vision condition - Cause: eye lens loses its elasticity - LOSS of accommodation = farsightedness - Also corrected using converging lens Myopia: near-sightedness - Eye can focus light from nearby objects onto retina: seeing up close is not difficult, seeing things at a distance is difficult - Causes: distance between the lens and retina is too large or cornea-lens combination converges too strongly - Light from distant objects brought to focus in front of retina -Solution: needs help diverging light rays, so a diverging lens will correct -The actual glasses lens is modified from a basic diverging lens shape and is called a negative meniscus GLASS SHAPES Positive meniscus: a converging lens Thicker in the middle Used to correct far-sighted vision Negative meniscus: a diverging lens Thinner in the middle Used to correct near-sighted vision CONTACT LENSES - a lens placed directly on the cornea - Invisible, used to treat near and far sightedness - Can be a positive of negative miniscule  OPTICS UNIT SUMMARY EM Spectrum from longest wavelength to shortest radio, microwave, infrared, visible light, ultraviolet, x-ray, gamma ray Wavelength The distance between crests of waves, such as those of the electromagnetic spectrum., The distance from any point on a wave to an identical point on the next wave Frequency the number of waves produced in a given amount of time Radio waves The electromagnetic waves with the longest wavelengths and lowest frequencies Microwaves EM waves with higher frequncies than radio, but lower than infrared; used for radar, cell phones, cooking. Infrared Electromagnetic waves of frequencies slightly lower than the red of visible light; heat lamps give this off. Visible light the only part of the electromagnetic spectrum seen by the human eye Ultraviolet waves that are part of the electromagnetic spectrum and can't be seen by the eyes; they have a higher frequncy than visible light but a lower frequency than x-rays x-ray EM waves of freuencies lower than gamma rays, but higher than ultraviolet gamma rays Electromagnetic waves with the shortest wavelengths and highest frequencies