LIGHT Narrated WEEK 2 LECTURE 2

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Slide 1:

Light

Sources of light :

Sources of light The Sun - Luminous Star – Producing light from the nuclear “fusion” reaction of Hydrogen being converted to Helium Producing light by product of this reaction is “light” energy The Sun (luminous) versus the Moon (non-luminous) reflects light Incandescent Glowing with visible light from high temperatures Flames from a fire, incandescent light bulbs heated wire, element in a stove

Sources of light :

Sources of light Fluorescent Glowing from gas-discharge that uses electricity to excite vapor. Fluorescent lamps convert electrical power into useful light more effeciently than an incandescent lamp. Compact fluorescent lamp ( CFL ), is a fluorescent lamp that replaces an incandescent lamp in light fixtures. Use less energy to produce same lumens. Lumens – “visible” light emitted.

Electromagnetic Spectrum:

Electromagnetic Spectrum Transverse waves Frequency depends on acceleration of electric (magnetic) charge Greater the acceleration, higher the frequency Shorter the wave, higher the frequency Higher the frequency, greater the energy.

Electromagnetic Spectrum visible light:

Electromagnetic Spectrum visible light Visible light is a very small portion of the electromagnetic spectrum 350 to 750 nm frequency Colors of the rainbow – ROY G BIV Red, Orange, Yellow, Green, Blue, Indigo, Violet

Electromagnetic Spectrum:

Electromagnetic Spectrum Ultra-violet radiation – causes skin cancer high energy Infra-red radiation – invisible “heat” Night vision goggles

Electromagnetic Spectrum:

Electromagnetic Spectrum Plants use specific wave lengths of light Chlorophyll pigments Why are plants green? Reflect green light frequency

Properties of light - two models:

Properties of light - two models Light ray model Particle-like view Photons travel in straight lines Applications Mirrors Prisms Lenses Wave model Traces motions of wave fronts

Light interacts with matter:

Light interacts with matter Interaction begins at surface and depends on Smoothness of surface Nature of the material Angle of incidence Possible interactions Reflection Refraction Absorption Transmission Transparent materials transmit light Opaque materials do not allow transmission of light Reflect, absorb or combination

Diffuse reflection :

Diffuse reflection Most common visibility mechanism Each point reflects light in all directions Bundles of light from object are seen by the eye Colors result from selective wavelength reflection/absorption

Image formation:

Image formation Real image Can be viewed or displayed at its location Example - movie image on a screen Virtual image Appears to come from a location where it is not directly visible Examples: plane mirror, convex mirror, concave mirror

Refraction :

Refraction Light crossing a boundary surface and changing direction Magnitude of refraction depends on: Angle that light strikes surface Ratio of speed of light in the two transparent materials Incident ray perpendicular to surface not refracted

Refraction, cont. :

Refraction, cont. Mirages Critical angle Light refracted parallel to surface No light passes through surface - “total internal reflection” Applications - fiber optics, gemstone brilliance Index of refraction A measure of light speed Substance Index of refraction Light speed Air Approx. 1 ~c Water 1.333 0.75c Glass 1.5 0.67c Diamond 2.4 0.42c BE condensate 18,000,000 38 mph!

Optics :

Optics The use of lenses to form images Concave lenses Diverging lenses Vision correction/in association with other lenses Convex lenses Converging lenses Most commonly used lens Magnifiers, cameras, eyeglasses, telescopes, …

The human eye:

The human eye Uses convex lens with muscularly controlled curvature to change focal distance Nearsightedness (myopia) - images form in front of retina Farsightedness (hyperopia) - images form behind retina Correction - lenses (glasses, contacts) used to move images onto retina

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