Light and the EM Spectrum

Electromagnetic Radiation

• EMR requires no medium to travel- can travel thru a vacuum

• Speed• 300,000 kilometers /sec• 186,000 miles /sec

• Consists of changing electric and magnetic fields

Changing electric and magnetic fields• Electric field is a region where particles can be pushed or pulled.

• Wherever there is an electric charge there is an electric field associated w/it.• A moving electric charge is part of an electric current• An electric current is surrounded by a magnetic field

• A magnetic field is a region in which magnetic forces are present• When electric field changes – so does the magnetic field.

EMR - Wave or Particle?• Acts like a wave sometimes – ie: Polarizing Filter

EMR - Wave or Particle?• Acts like a particle, a photon, sometimes – ie: Photoelectric Cell

EMS waves• Long wavelength : Low Frequency & Low Energy• Short wavelength : High Frequency & High Energy

Radio & Microwaves• Longest wavelengths & lowest

frequency of the EMS– Include Am, FM and Television

frequencies• AM – Amplitude modulation:

same frequency waves just a change in the amplitude to get different sounds etc.

• FM – Frequency Modulation: slight changes in frequency

Microwave & Infrared EMR• Microwave: used in microwave ovens & cellular phones• Infrared: Fast Food Heat Lamps, use as a night time

surveillance tool.

Visible Light

• White light is a mixture of the entire visible light spectrum

UV, Xray & Gamma rays• UV from the Sun helps the body produce vitamin D, too much exposure can

cause skin cancer • Xrays: used extensively in medicine to see “into” the body• Gamma Rays: used in medicine to treat cancer or destructive radiation from

nuclear explosions.

Reflection & Mirrors

• When light strikes an object it is either reflected, absorbed or transmitted.

– Opaque: a material that reflects or absorbs the light – can’t see through it. -wood

– Transparent: The material transmits light – allows light to pass through it– glass

– Translucent: allows some light to pass through – can’t see image clearly – wax paper, frosted glass.

Kinds of Reflections• You see objects because light is reflected, bounced off of it.• Law of Reflection: Angle of incidence equals the angle of reflection–

– Angle coming in = angle going off• Regular Reflection: reflection off smooth surface – a mirror• Diffuse Reflection: Irregular or bumpy, uneven surface – wall

Real or Virtual?• Image: a copy of an object formed by reflected or refracted light• Virtual image: right side up appears to be coming from behind the mirror.• Real Image: is formed when reflected light rays actually meet at a point.

The image is upside down (inverted),

3 Types of Mirrors• Plane Mirror: a flat mirror – produces an image that is right side (virtual) up and the same size

as the original object –• Concave Mirror: a mirror with a surface curved inward like a “cave” or a bowl.

– Light reflected comes together to meet at a Focal Point.– Can produce virtual or real images

• Convex Mirrors:– A mirror w/ a curved surface facing outward– Reflected rays appear to come from a focal point behind the mirror– Images formed are always Virtual

Concave mirror Convex mirror

Plane mirror

Refraction• RefractionRefraction of Light: BendBend or

change direction• 1. As light rays enter a new

medium the cause light to bend• 2. The denser the medium – the

slower the light travels• 3. Index of RefractionIndex of Refraction: a measure

of how much a medium bends the light that travels through it.

Prisms & Rainbows• PrismsPrisms: Separates white light into its component colors.

– The longer the wavelength, the less it will be bent by the prism.• RainbowsRainbows- light shining thru tiny droplets of water, each droplet

acts as a prism

Lens – Concave & Convex• Lenses – a curved piece of

material used to bend light– Concave lensesConcave lenses: as light

passes through, they are bent away from the center

• Images produced are only virtual, not real

– Convex lensesConvex lenses: cause light passing through to bend toward the focal point.

• The images produced depends on the position of the object

Concave Lens

Convex Lens

Color• The color of the object you see is the light that is

reflected from its surface. All other colors are absorbed by the object.

Primary & Secondary Light Colors• The 3 colors of light that can combine to form all other colors are primary primary

colorscolors –• a. Red, Blue, Green• i. Equal Red + Equal Blue = Magenta (secondary color)• ii. Equal Red + Equal Green = Yellow (secondary color)• iii. Equal Green + Equal Blue = Cyan (secondary color)• iv. Equal Red + Equal Green + Equal Blue = White

Magenta Yellow

Cyan

Primary + Secondary = White• Any 2 colors that combine to form white are complementary colorscomplementary colors• Secondary color + remaining Primary Color = White• Magenta + Green = White• Cyan + Red = White• Yellow + Blue = White

Magenta Yellow

Cyan

Pigments• PigmentPigment – substance that color other materials like paints, inks, etc• a. Primary Pigments are Cyan, Yellow & Magenta• b. Cyan + Yellow + Magenta = Black• c. Cyan + Yellow = Red• d. Yellow + Magenta = Red• e. Cyan + Magenta = Blue• f. The primary pigments are the secondary light colors!

Blue Red

Green

Compare Lights & Pigments• Three primary colors = three secondary pigments• Three primary pigments = three secondary colors

Vision - Structure

Need to know these structures & Need to know these structures & their function:their function:

• CorneaCornea: begins to focus : begins to focus lightlight

• Aqueous humorAqueous humor: fluid : fluid between inside of cornea & between inside of cornea & the outside of the lensthe outside of the lens

• IrisIris: the color of the eye. A : the color of the eye. A muscle that opens & closes muscle that opens & closes to regulate pupil sizeto regulate pupil size

• PupilPupil:: hole through which hole through which light passeslight passes

• LensLens:: flexible structure that flexible structure that focuses image on the retinafocuses image on the retina

Vision - StructureNeed to know these structures & their Need to know these structures & their

function:function:• Ciliary muscleCiliary muscle: ligaments : ligaments

attach the lens to these, they attach the lens to these, they contract & stretch the lens contract & stretch the lens allowing near & far focusallowing near & far focus

• Vitreous humorVitreous humor: fluid inside : fluid inside eyeball maintains size & eyeball maintains size & shape of the eyeshape of the eye

• Retina:Retina: contains the rods & contains the rods & cones that are sensitive to cones that are sensitive to lightlight

• Choroid coatChoroid coat: middle layer of : middle layer of the eyeballthe eyeball

• Sclera:Sclera: the outer “whites of the outer “whites of the eye”the eye”

• Optic nerveOptic nerve: takes rod & : takes rod & cone impulse back to the cone impulse back to the occipital lobe for processingoccipital lobe for processing

Image Processing

• FoveaFovea – – The central region where images focused is the fovea.

• RodsRods – about 1 billion, – about 1 billion, sensitive to brightness, sensitive to brightness, light and dark & light and dark & movementmovement

• ConesCones – detect color, – detect color, about 3 million. 3 types of about 3 million. 3 types of cones, sensitive to red, cones, sensitive to red, blue & green wavelengths blue & green wavelengths of light.of light.

• All rods & cones have All rods & cones have nerve fiber attached, these nerve fiber attached, these collect at the back of the collect at the back of the eye and form the eye and form the optic optic nervenerve which carries the which carries the signal back to the eye.signal back to the eye.