THE NATURE OF LIGHT

LET’S REVIEW What is a wave? A disturbance that transmits energy through matter or space. What do waves carry? Energy What is a medium? Substance wave travels through What kind of wave NEEDS a medium? Mechanical wave

MORE REVIEW What kind of wave DOES NOT NEED a medium? Electromagnetic wave What wave’s particles vibrate up and down perpendicular to the direction the wave is traveling? Transverse What wave’s particles vibrate back and forth? Longitudinal

EVEN MORE REVIEW What are the highest and lowest parts of a transverse wave? Crest and trough What are the “close together” and “far apart” parts of a longitudinal wave? Compression and rarefaction Transverse + longitudinal = Surface wave

CAN’T GET ENOUGH REVIEW Explain amplitude Height of wave = energy of wave Tall amp = high energy short amp = low energy Explain wavelength Dist between crest/crest, trough/trough, compression/compression, rarefaction/rarefaction Compare wavelength, frequency, and energy Long λ = low frequency = low energy Short λ = high frequency = high energy

ALMOST DONE WITH REVIEW What is reflection? Waves bounce back off barrier What is refraction? Waves bend at angle when changing media What is diffraction? Waves bend around barriers/go through openings What is interference? 2+ waves overlap and share the same space Contrast constructive interference and destructive interference. CI = crest over crest DI = crest over trough

IN YOUR OPINION, WHAT IS LIGHT?

WHAT IS LIGHT? LIGHT: is a type of energy that travels as a wave. Does NOT require a medium Also known as an ELECTROMAGNETIC WAVE An electromagnetic wave is a wave that can travel through space or matter and consists of changing electric and magnetic fields. A field is the place around an object that exerts a force without touching.

ELECTROMAGNETIC WAVE

WHAT IS DIFFERENT ABOUT THESE TWO WAVES?

LIGHT CONTINUED ALL electromagnetic waves are transverse waves. Electric fields vibrate and make a magnetic field The emission of energy in the form of EM waves is radiation

MORE LIGHT Light is produced when an electron loses the energy it gained when it jumped levels. A photon is a tiny “packet” of energy

HOW FAST IS LIGHT?

IT’S THE FASTEST THING IN THE UNIVERSE!!!!! The speed of light is 300,000,000 m/s or 3.0 x 108 m/s

LIGHT CAN TRAVEL AROUND THE EARTH 7.5 TIMES IN 1 SECOND!!!!! HOW FAST IS THAT REALLY!?! LIGHT CAN TRAVEL AROUND THE EARTH 7.5 TIMES IN 1 SECOND!!!!!

THE ELECTROMAGNETIC SPECTRUM or EMS

EMS Not all light can be seen There are many types of EM waves All EM waves travel at the same speed Speed = wavelength x frequency Same speed = different wavelength x different frequency Electromagnetic spectrum is the entire range of EM waves

EMS consists of seven categories of waves. RADIO WAVES MICROWAVES INFRARED VISIBLE LIGHT ULTRAVIOLET X-RAYS GAMMA RAYS

CAN YOU LABEL THE DIFFERENT WAVES ON THE PICTURES?

Long to short wavelength EMS EMS is arranged from: Long to short wavelength or Low to high frequency

CATEGORIES OF ELECTROMAGNETIC WAVES WHAT CAN YOU TELL ME ABOUT THIS WAVE? DECREASING WAVELENGTH AND INCREASING FREQUENCY R M I V U X G

CATEGORIES OF ELECTROMAGNETIC WAVES Longest λ and lowest frequency Low energy waves Used to broadcast radio signals Can not be heard, converted to sound AM = amplitude modulation FM = frequency modulation Radio waves Micro-waves Infrared Visible Light Ultra-violet X-rays Gamma rays

AM vs. FM Travels longer distance carry more information

Radio Waves RETURN

CATEGORIES OF ELECTROMAGNETIC WAVES Shorter λ and higher f than radio waves Carry more energy Ex. Televisions, cell phones, microwave ovens Radar(radio detection and ranging) = used for speed and location of vehicles Radio waves Micro-waves Infrared Visible Light Ultra-violet X-rays Gamma rays

How does a microwave work?

Microwaves RETURN

CATEGORIES OF ELECTROMAGNETIC WAVES Also known as IR Shorter λ and higher f than microwaves Carries more energy than radio and microwaves Feel warmth because of infrared Ex. Body heat, stars, planets, trees Warmer objects give off more infrared radiation Radio waves Micro-waves Infrared Visible Light Ultra-violet X-rays Gamma rays

Infra Red RETURN

CATEGORIES OF ELECTROMAGNETIC WAVES Narrow range of λs and frequencies ONLY light humans can see Different λ have different colors Longest λ is red = low energy = low frequency Shortest λ is violet = high energy = high frequency Colors of light = ROY G BIV Radio waves Micro-waves Infrared Visible Light Ultra-violet X-rays Gamma rays

Visible Light The Visible Spectrum Color Red 610-750 4.9-4.0 Orange Wavelength (nm) Frequency (x 1014 Hz) Red 610-750 4.9-4.0 Orange 590-610 5.1-4.9 Yellow 570-590 5.3-5.1 Green 500-570 6.0-5.3 Blue 450-500 6.7-6.0 Violet 400-450 7.5-6.7

Visible Light RETURN

CATEGORIES OF ELECTROMAGNETIC WAVES Also known as UV Produced by the sun Carry more energy than visible light Positive: kills bacteria, vitamin D, Negative: sunburn, skin cancer use sunscreen with a high SPF(Sun Protection Factor) Radio waves Micro-waves Infrared Visible Light Ultra-violet X-rays Gamma rays

Ultraviolet light

CATEGORIES OF ELECTROMAGNETIC WAVES Some of the shortest wavelengths and highest frequencies Easily penetrates materials Too much exposure can kill cells Radio waves Micro-waves Infrared Visible Light Ultra-violet X-rays Gamma rays

How do X-rays work?

X - Rays RETURN

CATEGORIES OF ELECTROMAGNETIC WAVES Carry the largest amount of energy Penetrates material very easily Exposed to gamma rays everyday but are not harmful Used to treat cancer, but some good cells can be killed Radio waves Micro-waves Infrared Visible Light Ultra-violet X-rays Gamma rays

Gamma Rays RETURN

Light Wave Interactions

Light waves bounce off an object Light Reflection Light waves bounce off an object Allows for you to see objects that don’t produce light

Law of Reflection The angle of incidence = angle of reflection Incidence = falling of light beam on surface

Why can we see ourselves in a mirror but not in a wall?

Regular/Specular Reflection Types of Reflection Regular/Specular Reflection Diffuse Reflection

Absorption Scattering More interactions Absorption Scattering Transfer of energy carried by light waves to particles of matter. Release of light energy by particles of matter that have absorbed energy

Absorption and Scattering

Light Refraction Bending of a wave at an angle as it passes from one medium to another. If light passes into a medium where the speed of light is slower, the light bends away from the boundary between the media. If light passes into a medium where the speed of light is faster, the light bends toward the boundary.

Refraction and Color Separation White light = combined colors of visible light Amount of light refracted depends on λ Short λ = ↑ bending Long λ = ↓ bending

SITE FOR WHITE LIGHT COLORS http://micro.magnet.fsu.edu/primer/java/scienceopticsu/refraction/refractionangles/index.html SITE FOR WHITE LIGHT COLORS

Light Diffraction Bending of waves around barriers or through openings Light diffraction is difficult to see Can not diffract much around large objects Causes shadow edges to be blurry

Diffraction and Interference http://www.acoustics.salford.ac.uk/feschools/waves/diffract3.htm Diffraction and Interference Constructive interference = bright light Deconstructive interference = dark light

Light and Color

Light interacts with matter by: Reflection Absorption Transmission

How is light interacting below? REFLECTION TRANSMISSION ABSORPTION

Passing of light through matter Transmission: Passing of light through matter

Easy to transmit light or not?

TRANSPARENT Light transmitted easily Can see object’s CLEARLY Ex. Air, glass, water, clear wrap

TRANSLUCENT Light transmits but also some scatters Hard to see objects Ex. Frosted glass, wax paper

OPAGUE Light not transmitted at all Cannot see objects at all Ex. Metal, wood, aluminum foil

Seeing Colors Occurs because of reflection, transmission, or absorption

What about opaque colors? White light shines on strawberry Red light is reflected All other colors absorbed

What about black and white? ALL colors are reflected to get color white ALL colors are absorbed to get color black

Transparent and Translucent Objects Green transmitted through material All other colors absorbed If clear, all colors transmitted

Mixing Colors of Light White light = all light combined or blue + green+ red(primary colors) Cyan Green Blue Yellow Magenta Red Secondary colors = 2 primary colors added together (blue + red = magenta) (red + green = yellow) (blue + green = cyan)

What color do you get when you mix blue, green, and red paint?

Mixing Colors of Pigment Can not mix primary colors to get white Paint contains pigments pigment: gives substance color by absorbing some light colors and reflecting others