What is it?

How does it work?

How do we use it?

Light

http://www.youtube.com/watch?v=DfPeprQ7oGc

o Electromagnetic Waves display wave behavioro Created by oscillating electric and magnetic

fieldso Electromagnetic Spectrum – range of

frequencies of EM waves

Dual Nature

o Visible light – the range of EM that produces light that we can detecto Radio and Microwaves are produced by placing

a magnetic field in an oscillating electric fieldo X-rays are produced when fast-moving

electrons strike a metal targeto Infrared from the sun is responsible for the

heating from the suno Gamma rays are emitted during nuclear

collisions

EM Spectrum

o Transverse waveso Nonmechanicalo All EM waves travel at the same

speed:o c = m/s

o Example: Red light with a frequency of Hz has what wavelength?

Characteristics

Concave - convergent (all rays come together)Real focal point (the rays REALLY intersect)

Convex – divergent (all rays spread apart)Virtual focal point (the rays SEEM to intersect

behind the mirror)Produces virtual images only

Mirrors - work by reflection

Convex – convergent Real focal point

Concave – divergent Virtual focal point Produces virtual images only

Lenses - work by refraction

o Vibrations in a vertical plane – vertical polarization

o Vibrations in a horizontal plane – horizontal polarization

o Polarization only exists for TRANSVERSE waves!!!

Polarization

o When polarized lenses overlap with axes perpendicular, no light passes through!

Polarization

o We all see color in different ways.o When light reaches our eyes, we do not see

just one frequency, but a variety of frequencies at various intensities.

o For example, white light is NOT a color! o It is the presence of all frequencies of visible lighto NOT the only way to produce white light!

o Primary Colors – any three colors that combine to form white light

Color Perception

o Most common primaries are red, green and blue

o Yellow, magenta, and cyan are secondary colors

o Colors add to form white lighto Colors subtract to form black!

Color Mixing

o Myth –”No one set of colors can produce all other colors”o Almost any three colors can be mixed to

produce the other colorso Colors can be mixed to get even the primary

colors!o They will never be as pure as the original

frequencyo Red, yellow, and blue are not even the best

primary set!

Color Mixing - myths

o When light encounters a different substance, part of the light is absorbed while the rest is REFLECTED!

o Texture of a surface determines how much reflection

o For flat mirrors: angle of incidence = angle of reflection

Reflection

𝜃=𝜃 ′

o Produces an UPRIGHT,

o VIRTUAL, SAME SIZE

o image

Ray Diagram – Flat Mirror

• Light can be approximated as rays!• Light produces two types of images:• REAL – these appear in front of the mirror on a ray

diagram• In reality, REAL images can be projected onto walls and

screens• VIRTUAL – these appear behind the mirror on a ray

diagram• In reality, VIRTUAL images can only be seen by looking

into the mirror• Ray diagrams help us predict image location,

orientation, similarity, and type of image (LOST)

Drawing Ray Diagrams – allows us to predict the location of an image

• Draw all rays from the top of the object.• The radius of curvature is the center of your circle;

the focal point is HALF that value.• Use a ruler and be exact.• RAY 1: Draw parallel to the principal axis, reflect

through the focal point.• RAY 2: Draw through the focal point, reflect parallel

to the principal axis• RAY 3: Draw through the radius of curvature; reflect

back on itself.• Image appears where the three reflected rays

intersect!

Rules (Curved Mirrors):

• f is the focal point of the mirror and is HALF the radius of curvature (it is NEGATIVE for a CONVEX mirror)

• p is object distance from the mirror• q is image distance from the mirror (it is

NEGATIVE for a VIRTUAL image)• h is object height• h’ is image height (it is NEGATIVE for

INVERTED images)

We can MATHEMATICALLY predict image formation also!!!!

=

o Defined as the bending of light as it travels from one medium to another

o Depends upon the index of refraction of the material…

Refraction

• Index of refraction, n, tells us how fast light travels in the medium• nwater = 1.33 (slower)• nglass = 1.5 (slowest)• nair = 1.00 (fastest)• Tells me how the light will bend:• Fastest to slower, light bends TOWARD THE NORMAL• Air to water• Slower to faster, light bends AWAY FROM THE NORMAL• Water to air

Refraction

• Ray 1: Parallel to the principal axis to middle of lens. Refract through BACK focal point.

• Ray 2: Through the FRONT focal point to middle of lens. Refract parallel to principal axis.

• Ray 3: Through lens center.

Lens Ray Diagrams

• Waves spread when they pass through an opening

Diffraction