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

fields

o Electromagnetic Spectrum – range of frequencies of EM waves

Dual Nature

o Visible light – the range of EM that produces

light that we can detect

o Radio and Microwaves are produced by placing a magnetic field in an oscillating electric field

o X-rays are produced when fast-moving electrons strike a metal target

o Infrared from the sun is responsible for the heating from the sun

o Gamma rays are emitted during nuclear collisions

EM Spectrum

o Transverse waves

o Nonmechanical

o 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 light

o 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 colors

o Colors can be mixed to get even the primary colors!o They will never be as pure as the original

frequency

o 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