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Physics: Optics
Isaac Newton said: - โ
Light moves as tiny particles Huygens said: - โ
Light is a wave Ray Model of Light - โ
Light is represented as a ray (arrow) which travels in a straight line. The ray model was introduced as a way to study how light interacts with matter, regardless of whether light is a particle or a wave. Ray optics or geometric optics. Sources of Light - โ
Luminous source (sun) produces own light. Illuminated source (moon) reflects light. Opaque - โ
Does not allow light to pass through Translucent - โ
Light passes through but objects not seen clearly Transparent - โ
Light passes through and objects seen clearly Ole Roemer - โ
Danish astronomer; first to first to determine that light travels with a measurable speed. Albert A. Michelson - โ
1926: measured speed of light. For this work, be became the first American to receive the nobel prize in science.
Speed of light - โ
c = 3 ร 10^8 m/s (precise enough) At this rate, light travels 9.46 ร 10^12 km in a year. This is called a "light year" Light diffraction - โ
Light bends around a barrier Light refraction - โ
Light divides into colors, a property of waves (not particles). ROY G BIV Ray model of light - โ
This assumes that light travels in straight-line paths called rays Geometric Optics - โ
When we use the ray model of light to deal with optics (I think) The law of reflection - โ
when the angle of incidence equals the angle of reflection Diffuse reflection - โ
When light is reflected in many directions because of a rough surface (even if it's microscopically rough, like paper) specular reflection - โ
reflection from a mirror Plane mirror - โ
A mirror with a smooth, flat, reflecting surface. Image distance = object distance Virtual image -
The mirror equation - โ
Relates the object and image distances to the focal length ฦ. Mirror magnification - โ
The height of the image divided by the height of the object Index of refraction - โ
n: The ratio of the speed of light in vacuum to the speed "v" in a given material. Snell's Law - โ
The angle of refraction depends on the speed of light in the two media and on the incident angle. An analytical relation between theta-1 and theta-2 was arrived at experimentally about 1621 by Willebrord Snell. Critical angle - โ
When light passes for one material into a second material (ie from water to air) and the angle of refraction is 90 degrees (for a specific incident angle) and the refracted ray would skim the surface. Total internal reflection - โ
When the incident angle is creater than the critical angle and the ray is not refracted at all, but all of the light is reflected. (can only occur when light strikes a boundary where the medium beyond has a lower index of refraction) Fiber optics - โ
A bundle of tiny fibers (a light pipe) where light is transmitted with practically no loss as a result of total internal reflection. The critical angle is never exceeded, and rays only glance off the walls. Light pipe/cable - โ
A bundle of tiny glass and plastic fibers as thin as a few micrometers. Diopter - โ
The unit for lens power
Lens - โ
Uses refraction do produce a real or virtual image Converging lens - โ
When parallel rays are focused to a point (focal point) Diverging lens - โ
After parallel rays pass through a diverging lens, they appear to diverge from a point, its focal point; and the corresponding focal length is considered negative. The lensmaker's equation - โ
Relates the raii of curvature of the lens surfaces and the lens' index of refraction to the focal lenglth of the lens. Huygen's Principle - โ
Every point on a wave front can be considered as a source of tiny wavelets that spread out in the forward direction at the speed of the wave itself. The new wave front is the envelope of all the wavelets--that is, the tangent to all of them. Diffraction - โ
The bending of waves behind obstacles into the "shadow region." Only occurs for waves, not particles. Monochromatic - โ
Plane waves of light of a single wavelength Wave-interference - โ
From Young's double slit experiment. Constructive interference - โ
When the amplitudes of the two waves add to form a larger amplitude. Destructive interference -
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A type of diffraction grating that is made by ruling fine lines on a metallic or glass surface from which light is relected and analyzed. (Analysis is basically the same as for a transmission grating) Double-slit vs. multiple-slit pattern - โ
Bright maxima are much sharper and narrower for a grating. Diffraction pattern - โ
Interference of waves diffracting around something in a pattern. Exists around any sharp object illuminated by a point source. Maximum light intensity - โ
Occurs at theta = 0 Spectrometer/spectroscope - โ
a device to measure wavelengths accuratly using a diffraction grating (or a prism) to separate different wavelengths of light. Line spectrum - โ
Occurs when a gas is heated or an electric current is passed through it. Only certain discrete wavelengths of light are emitted, and these are different for different elements and compounds. Continous spectrum - โ
The light from heated solids, such as a lightbulb filament, and even from a dense gaseous object such as the Sun, produces a continuous spectrum including a wide range of wavelengths. Absorption lines - โ
Atoms and molecules can absorb light at the same wavelenghts at which they emit light. The Sun's absorption lines are due to absorption by atoms and molecules in the coller outer atrmosphere of the SUn, as well as by atoms and molecules in the Earth's atmosphere. Thin-film interference -
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When colors are a result of constructive interference between light reflected from the two surfaces of the thin film. The effect is present only if the thickness of the film is on the order of the wavelength of the light. Newton's rings - โ
WHen a curved glass surface is placed in contact with a flat glass surface, a series of concentric rings is seen when illuminated from a bove by a monochromatic light. They are due to interference between rays reflected by the top and bottom surfaces of the very thin air gap between the two pieces of glass. This gap is equivalent to a thin film. Michelson interferometer - โ
Instrument involving wave interference which can precisely measure wavelengths. Beam splitter - โ
A component of the Michelson interferometer which is half-silvered and this allows half of the light to go through, and reflects half of the light. Linearly polarized / Plane-polarized - โ
Oscillations are in a plane. Only exists for transverse waves. Unpolarized - โ
The source has oscillations in many planes at once. Polaroid sheet - โ
A sheet where complicated long molecules are arranged parallel to one anoghter. These arrangements act like slits so that only one orientation of polarization can pass through (nearly undiminished). Transmission axis - โ
The direction which waves are allowed to pass through Polarizer -
Angular magnification / magnifying power - โ
M: the ratio of the angle subtended by an object when using the lens, to the angle subtended using the unaided eye, with the object at the near point N of the eye.
