Bell Ringer Explain one of the stations from yesterday in detail.

Light CP Physics

Predictions of Light What do you picture light to look like? How fast is light?

Early Concepts of Light Several early scientists claimed that light travels in transverse waves According to Einstein, light consists of particles called photons Photon: Massless bundles of concentrated energy

The Speed of Light Early scientists used the periods of objects in our solar system to estimate the speed of light Later, experiments using reflected light from mirrors were used Through these experiments, the speed of light through a vacuum was found to be: 300,000 km/s = 186,000 mi/s

Electromagnetic Waves Light is energy emitted by accelerating electric charges, usually electrons This energy travels in a wave that is partially electric and partially magnetic These are electromagnetic waves Visible light is a very small portion of the electromagnetic spectrum

Electromagnetic Waves Can be transmitted in a way that they can be deciphered later Radio waves Unlike sound waves Electromagetic waves do not require a medium i.e. They can travel through space

Electromagnetic Spectrum

Bell Ringer EM Spec Quiz

Bell Ringer Read 3D TV article Answer the following How do 3D TVs work? Why do 3D TVs block the view of just one eye?

Opaque and Transparent Materials Transparent: Materials which allow light to pass through Electrons receive energy from the entering light wave and re-emit this energy as light Opaque: Materials which do not allow light to pass through Electrons receive energy from the entering light wave and passes it onto neighboring atoms This energy is converted to random kinetic energy and the materials become slightly warmer

Shadows Ray: A thin beam of light When light shines on an object, some of the rays may be stopped while others pass Shadows are formed where light rays cannot reach

Shadows A shadow usually consists of a dark region on the inside, and a light region on the outside Umbra: A total shadow Penumbra: Partial shadow appearing where some light is blocked, but other light fills in

Umbra and Penumbra in a Solar Eclipse

Structure of the Eye

Human Eye What we see can be distorted Our mind’s interpretation of an image can be altered

Bell Ringer 1.) What is the difference between opaque and transparent? 2.) What is the difference between the umbra and penumbra?

Intensity The intensity of light depends on the light source The intensity is also dependent on the distance from the source Larger the distance – smaller the intensity Smaller the distance – greater the intensity

Shadows Remember… Umbra: A total shadow Penumbra: Partial shadow appearing where some light is blocked, but other light fills in What happens to each as we increase the distance?

Law of Reflection Reflection- When a wave reaches a boundary between two media, some or all of the waves bounce back Θ 1 =Θ 2 Θ 1 is the incident incoming angle Θ 2 is the reflected outgoing angle Ex: 60° incident 60° reflected

Mirrors Mirrors use the law of refection to show images Real image: all of the light rays show where the image actual is Virtual image: can be seen by an observer but cannot be shown on a screen because the light rays do not come together

Refraction Sound waves travel at different speeds depending on the medium Light has the same property

Refraction (Snell’s Law) Light travels at different speed depending on the medium Index of refraction (n) N= speed of light in vacum/speed of light in medium Or n=c/v Air has an index of refraction of about 1

Snell’s Law Light’s angle in the medium is dependent on both the index of refraction and the incident angle n 1 sinθ 1 =n 2 sinΘ 2 Example: A laser light ray enters a cup of water (n=1.33) from air (n=1) at an angle of 15°. What is the outgoing angle?

Refraction Demos Bowl of Water Test Tube Pickle Jar

Bell Ringer A light ray hits a mirror at 15.6°. What is the reflected angle? Give an example where there is evidence of the following… Light being reflected Light being refracted

Polarization Some light is polarized, meaning its waves are confined to a 2-D plane A single vibrating electron will produce polarized light Common light sources emit non- polarized light since the electrons vibrate randomly in all directions

Polarization Filters

Polarization

Polarization and 3-D Viewing Vision in three dimensions depends on the fact that each eye views a scene from a slightly different angle

Bell Ringer What does a polarized filter do? How are they used to view 3D movies?

Total Internal Reflection At some angle (dependent on the medium) all of the light rays will be reflected back into the medium and not leave. Applications Fiber optic cable Sparkling Diamonds

Curved Mirrors Two ways to observe a curved mirror Converging concave ) Diverging convex (

Curved Mirrors Concave lens – parallel rays converge at the focal point Focal length – distance from lens to focal point We can examine an image formed by the lens by only examining a number of rays

Ray Tracing Principle rays 1.) Top of Image, then through F 2.) Through F 3.) Through middle vertex

Bell Ringer What is the difference between a real and a virtual image?

Lens Applications Binoculars

Telescopes

Microscope

Glasses

The Color Spectrum Spectrum: A spread of wave frequencies White Light: The combination of all colors Under white light: White objects appear white Colored objects appear in their individual colors Therefore, white is not a color, but a combination of all colors

The Color Spectrum Black is similarly not a color, but the absence of light Black objects absorb some light of all visible frequencies Not all light is absorbed by black objects

Color by Reflection When electrons receive energy, they become become excited and then transfer this extra energy outward Some energy is absorbed into the material The rest of the light is reflected outward giving an the appearance of color

Color by Reflection Objects can ONLY reflect frequencies present in the light shining on them For example: If a red light shines on a blue object, the object will appear black because there is no blue in the light for the object to reflect back.

Color by Transmission The color of a transparent object depends on the color of light it transmits Pigment: The material in the glass that selectively absorbs colored light Electrons in the pigment are responsible for this absorption Any absorption results in an increase in temperature of the material

Bell Ringer Why do red objects appear red? Draw the ray diagram for an image when an object is placed inside the focal point in front of a converging lens.

Retinal Fatigue

Diffraction Light behaves as a wave to cause light and dark spots (constructive and deconstructive) interference Applet Ex: Snowman Glasses

Mixing Colored Light Light of all the visible frequencies mixed together produces white light This can be achieved by mixing only blue, red, and green light of equal brightness

Mixing Colored Light A lmost any color can be made by overlapping light of three colors by varying the brightness of each Combining red, green, and blue produces the highest number of different colors For this reason, red, green, and blue are known as additive primary colors

Additive Primary Colors Red + Green = Yellow Red + Blue = Magenta Blue + Green = Cyan

Complimentary Colors Complimentary Colors: Two colors, which when added together, produce white Yellow + Blue = White Magenta + Green = White Cyan + Red = White

Atomic Spectra Every element has its own color when made to emit light In gas form, atoms are far apart Their vibrations will not be interrupted by neighboring atoms Neon – Red Mercury – Blue-Violet Helium – Pink Spectroscope: An instrument which breaks glowing elements into a series of colored lines

Atomic Spectra This pattern is called a line spectrum Each line corresponds to a specific frequency of light Line spectrums are the “fingerprints” of each element

Atomic Spectra Hydrogen : Helium : Carbon : Continuous :