chapter 16. ray model of light- light is represented as a ray that travels in a straight line
TRANSCRIPT
FUNDAMENTALS OF LIGHT
Chapter 16
16.1 ILLUMINATION
Ray Model of Light- Light is represented as a ray that travels in a straight line.
SOURCES OF LIGHT 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
LUMINOUS FLUX (P)
The rate at which light rays come out of a luminous source
Luminous flux is measured in lumens (lm)
ILLUMINANCE (E)
The rate at which light strikes the surface Illuminance flux is measured in lux (lx)
REVERSE SQUARE RELATIONSHIP
The illuminace produced by a point source is proportional to 1/r2
Illuminance is dependent on the radius.
As radius increases, the illuminance decreases.
LUMINOUS INTENSITY
The luminous flux that falls on 1m2 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
POINT SOURCE ILLUMINANCE
P increases, E increases r decreases, E increases
Illuminance in lux (lx) Luminous flux in lumens (lm)
EXAMPLE PROBLEM 1 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=?
THE SPEED OF LIGHT
Light is an electromagnetic wave It carries energy The only portion of waves that can be
seen by the human eyeElectromagnetic spectrum consists of:
radio MicrowaveInfraredvisible UltravioletX-raysGamma rays
LIGHT CONT. As you go from left to right from the list: Radiolong , 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 108 m/s
THE UNIFYING CONCEPTS OF SCIENCE
Systems, Order, and organizationThe 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 ExplanationIn order to explain a system, models like this one are made for an explanation.
Form and functionWaves of different wavelengths have different properties
THE WAVE NATURE OF LIGHT
Diffraction- bending of light around a barrierColor 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
COLOR CONT.
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
COLOR CONT.
Subtractive Primary Pigment colorsCyan, magenta, yellow-absorbs only one primary color and reflects two from white light
Cyan absorbs red, reflects blue and greenMagenta absorbs green, reflects red and blue
Yellow absorbs blue, reflects red and green
POLARIZATION OF LIGHT
production of light in a single plane of oscillation
Light produced from a bulb or the sun is unpolarized lightit vibrates in more than one plane, i.e., horizontal and vertical planes
HOW DOES POLARIZATION OCCUR?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
POLARIZATION CONT.
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 directionsunpolarized light
POLARIZATION ANALYSIS
Use Malus’s law to compare the light intensity coming out of polarizing filter.
I2= I1cos2Ø
Angle between polarizing axes
Intensity of filter 1
Intensity of filter 2
SPEED OF LIGHT WAVE
ƛ= c/f ƛ=wavelength c- speed of light f- frequency
ƛ
DOPPLER EFFECT
fobs= f (1 +/- v/c) The Doppler Effect for light has
been used be astronomers. Written in terms of wavelength
Doppler Shift (ƛobs – ƛ) = ∆ƛ = +/-( v/c)ƛ
Red shifted positive change in wavelength
Blue shifted negative change in wavelength