LightChapter 13

Ch13 Sec 1The Behavior of Light

Light and Matter

• Objects must reflect light to be seen.– Opaque materials do not allow light to pass

through them; they only absorb and reflect light

Light and Matter

• Objects must reflect light to be seen.– Opaque materials do not allow light to pass

through them; they only absorb and reflect light– Some light passes through translucent materials.

Light and Matter

• Objects must reflect light to be seen.– Opaque materials do not

allow light to pass through them; they only absorb and reflect light

– Some light passes through translucent materials.

– Transparent materials allow almost all light to pass through them; only a little light is absorbed and reflected.

Reflection of light

• Reflection of light – a light wave strikes an object and bounces off.

• Law of Reflection – angle at which light strikes a surface is the same as the angle at which it is reflected

Regular Reflection

• Regular reflection – reflection of light waves from a smooth surface

Diffuse Reflection

• Diffuse reflection – reflection of light waves from a rough surface

Refraction of Light

• Refraction of light - change in the speed of a light wave when it passes from one material to another

Index of refraction

• The index of refraction indicates how much a material reduces the speed of light; the more light is slowed, the greater the index of refraction.

Prisms

• Separate white light into visible spectrum based on light wavelength

Rainbows

• Caused by water droplets refracting wavelengths of sunlight

Chapter 13 Section 2Light and Color

Colors…• Colors are determined by wavelength

of light an object reflects.–White objects reflect all colors of

visible light.–Black objects absorb all colors of visible

light.

Colors…• Colors are determined by wavelength of light an

object reflects.– White objects reflect all colors of visible light.– Black objects absorb all colors of visible light.

– Filter – is a transparent material that absorbs all colors except the color or colors it transmits• Filters can make

objects appear to be different colors.

Seeing Color

• Light enters the eye and is focused on the retina.– Retina – made up of two types of cells that absorb

light

Seeing Color…• Light enters the eye and

is focused on the retina.– Retina – made up of two

types of cells that absorb light• Cones – distinguish colors

and detailed shapes; most effective in daytime vision

• Rods – sensitive to dim light; most effective in nighttime vision

Colorblindness Tests

Test Name: Ishihara Test

Colorblind sees:yellow square

Normal color:yellow square &

faint brown circle

Colorblind sees:the number 17

Normal Color sees:the number 15

Colorblindness

• Results from when one or more sets of cones do not function properly

Mixing colors•Pigment – colored material

that absorbs some colors and reflects others

Mixing colors

• Pigment – colored material that absorbs some colors and reflects others

• Primary colors of light – Red, Green, and Blue• Primary colors of pigment – magenta, cyan, and yellow

Mixing colors• Pigment – colored material that absorbs some colors and reflects others• Primary colors of light – Red, Green, and Blue• Primary colors of pigment – magenta, cyan, and yellow

• Primary colors of light are additive colors – combine to form white

• Primary colors of pigments are subtractive colors – combine to form black, the absence of reflected light

Producing LightChapter 13 Section 3

Incandescent lights

• Hot tungsten wire glows; gives off light and heat

Fluorescent lights

• Electrons collide with gas atoms, releasing ultraviolet radiation absorbed by phosphorus lining the bulb; gives off light

Why are these better than Incandescent bulbs?– Less energy used– longer lasting

Neon lights

• Tubes filled with gas (usually neon) produce light from electron collisions; different colors can be made by adding different gases

Sodium-vapor lights

• Heated neon gas glows and warmth turns sodium into a vapor, producing a yellow-orange glow; used for outdoor lighting.

Tungsten-halogen lights

• Have a filament and gas enclosed in a glass bulb to produce intensely bright light

Lasers

• Light beam produced when identical atoms send off identical light waves; can be made from gases, liquids, or solids

• FYI – LASER – Light Amplification by Stimulating Emissions of Radiation

Lasers• Light beam produced when

identical atoms send off identical light waves; can be made from gases, liquids, or solids

• Lasers produce coherent light – waves of some wavelength are aligned, and travel same direction– Incoherent light – waves of

multiple wavelengths are not aligned, travel in many directions

Using Light

Chapter 13 Section 4

Holography• Process used to create a three-dimensional

photographic image of an object– Illuminating objects with laser light produces holograms.– Holographic images are difficult to copy.

Optical Fibers

• Use a process called Total Internal Reflection in order to transfer information coded in light beams.– Total internal reflection – light strikes a surface

between two materials and is completely reflected back to the first material.

Total internal reflection