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