Light: Waves and Particles• Like a wave … light shows interference (reflect, refract,

diffract, standing waves) does not require a medium• Like a particle, light can move electrons• So light is described as having a dual nature• Comes in “packets” called photons (more like

bundles of energy)• Amount of energy directly proportional to frequency.

Higher freq. = more energy.• Indirectly proportional to wavelength. Bigger wave

= less energy• Speed of light 3 x 108 m/s in vacuum• Speed changes for medium, but not significantly,

slows down for denser media

Electromagnetic spectrum• all possible kinds of light, classified

according to frequency and wavelength• Radio/TV Waves …lowest energy,

used in communication• Microwaves…used in cooking and

communication• Infrared Waves… felt as warmth• Visible light…we can see ROYGBIV• Ultraviolet waves…cause sunburn• X Rays… used in medicine• Gamma Rays… used in medicine• Stars, like the sun, give off all of these

forms of energy

Light Rays• use lines called rays to see

where light goes• rough surfaces reflect the rays in

all directions• smooth surfaces reflect the

light in one direction• the angle light rays come in at

equals the angle it’s reflected at.• Angle of Incidence equal the

Angle of Reflection (Law of Reflection)

• Angles are measured between the ray and an imaginary line perpendicular to the surface called the normal.

• movie: Law of Reflection

Mirrors• Plane (flat) mirrors form virtual

images inside of the mirror. Virtual images are from where

light appears to come from, not the actual path.

• Curved mirrors distort the image, but make real images. Real images form when light rays come together at a certain point

• movie: comparing real and virtual images

Color• Light hits objects. • Many wavelengths are absorbed

by the object and not seen by you.

• Wavelengths that are reflected are seen by you as color.

• Technically, you don’t see something, you see light bouncing off of something.

• Colors can add together to make new colors (e.g. light. White light = all colors of light, black = absence of light)

• Colors can subtract to make new colors (e.g. pigments, black paint = all colors of paint, white paint = absence of color)

• movie: additive color mixing

Refraction• Light bends as it goes

from one substance (medium) to another because it changes speed

• Compare the bend to the normal, just like reflection

• Light bends towards the normal when it enters a denser medium and slows down

• Light bends away from the normal when it enters a less dense medium

and speeds up

Lenses• Mirrors and lenses can be curved out

(convex) or can curve in (concave … like a cave).

• movie: converging and diverging lenses

Light Rays• There’s an angle called the critical

angle, where light will not go back out of something and just keeps bouncing back around inside.

• Diamonds are cut like this to keep the light from leaving and fiber optic cables are made so that light does not escape.

• movie: Total Internal Reflection