# Chapter 16.  Ray Model of Light- Light is represented as a ray that travels in a straight line.

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Chapter 16

 Ray Model of Light- Light is represented as a ray that travels in a straight line.

 Lumonous source- object that emits light  Iluminated source- object becomes visible as a result of light reflecting off.  Opaque media- do not transmit light but reflect some light  Transparent media- transmit light  Translucent media- transmit light but does not permit object to be seen

 The rate at which light rays come out of a luminous source  Luminous flux is measured in lumens (lm)

 The rate at which light strikes the surface  Illuminance flux is measured in lux (lx)

 The illuminace produced by a point source is proportional to 1/r 2  Illuminance is dependent on the radius.  As radius increases, the illuminance decreases.

 The luminous flux that falls on 1m 2 of the inside of a 1-m-radius sphere  Luminous flux is measured in Candela (cd).  Based on the human perception of light.  Not very reproducible

 P increases, E increases  r decreases, E increases Illuminance in lux (lx) Luminous flux in lumens (lm)

 Illumination of a surface- what is the illuminace at, on your desktop, if it is lighted by a 1750-lm lamp that is 2.5 m above your desk?  P= 1750 lm  r= 2.50 m  E=?

 Light is an electromagnetic wave  It carries energy  The only portion of waves that can be seen by the human eye Electromagnetic spectrum consists of: radio Microwave Infrared visible Ultraviolet X-rays Gamma rays

 As you go from left to right from the list:  Radio  long, low frequency, more wavelike  Gamma rays  short, high frequency, more particle like  Visible Light consists of what colors:  Red, orange,yellow, green, blue, indigo, and violet  Speed of light(c) = 3.00 x 10 8 m/s

Systems, Order, and organization The wavelength s of these waves can easily be predicted because there is an observable pattern As it pertains to the Electromagnetic Spectrum Change, constancy, and measurement. All the waves on the electromagnetic spectrum can be measured with the same equation used to measure waves. Evolution and equilibrium. New discoveries has changed the system until there is little or no change in the model. Evidence, Models and Explanation In order to explain a system, models like this one are made for an explanation. Form and function Waves of different wavelengths have different properties

Diffraction- bending of light around a barrier Color  Why do objects appear to have certain colors?  They reflect that particular color(wavelength)  Atoms/molecules in an object have certain natural frequencies at which they selectively absorb energy

Additive Primary Colors Red, Blue, Green -when added together, will produce white light - primary colors when mixed produce the secondary colors : yellow= red + green magenta= red + blue cyan= blue + green

Subtractive Primary Pigment colors Cyan, magenta, yellow -absorbs only one primary color and reflects two from white light Cyan absorbs red, reflects blue and green Magenta absorbs green, reflects red and blue Yellow absorbs blue, reflects red and green

 production of light in a single plane of oscillation  Light produced from a bulb or the sun is unpolarized light  it vibrates in more than one plane, i.e., horizontal and vertical planes

By Filtering with a Polaroid Filter - the Polaroid filter is made of a special material which is capable of blocking one of the 2 planes of vibration -after it has been filtered, it will only have ½ the light intensity

By Reflection -light can be polarized off of a nonmetallic surface ( road surface or water) because the reflected light has a large concentration of vibrations in a parallel plane to the surface Metallic surfaces reflect a variety of vibrational directions  unpolarized light

 Use Malus’s law to compare the light intensity coming out of polarizing filter. I 2 = I 1 cos 2 Ø Angle between polarizing axes Intensity of filter 1 Intensity of filter 2

 ƛ = c/f  ƛ =wavelength  c- speed of light  f- frequency ƛ

 f obs = f (1 +/- v/c)  The Doppler Effect for light has been used be astronomers.  Written in terms of wavelength  Doppler Shift  ( ƛ obs – ƛ ) = ∆ ƛ = +/-( v/c) ƛ  Red shifted positive change in wavelength  Blue shifted negative change in wavelength

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