Introduction to Light

*Electromagnetic Waves- Produced by the oscillation of a _______ particle.- Particles radiate coupled ________ and _________ fields that oscillate perpendicular to each other.- Two __________ transverse waves.- No medium required.- Speed of electromagnetic waves (EM) in a vacuum (c)

c = __________________- Velocity = ________________ x _______________- Dual nature of light:

1. _______ _________2. Photon = particle like bundles of __________

*Electromagnetic Spectrum- Classification of the EM waves according to their ________ & ________.- ______ wavelength EM waves have low frequencies.- ______ wavelength EM waves have high frequencies.- High frequency EM waves have higher energy.

Visible Spectrum (400nm – 700nm)- Spectrum – band of _________ produced when light is broken into its constituent wavelengths

- Prism produces spectrum by ___________.- Red refracts least because it has __________ wavelength.

*Source of Light

- Light is emitted by _________ that fall from higher to ________ energy state and give off EM waves. When this emitted EM wave is visible we see light.

- The different orbits in an atom are like steps. When an ______ is raised to a higher orbit, the atom is “__________” and becomes unstable. When the electron falls to its original step (more _______), it releases energy in the form of light (__________).- The energy of the emitted photon is equal to the difference in the 2 energy levels, obeying E = hf where h is Planck’s constant (_________________)

*Spectroscopy - Bright line Spectrum (Emissions Spectrum)

- Each element has its own characteristic ________ levels, thus transition of electrons between these levels result in each element emitting its own characteristic ____________ of light.- Gas atoms emit _______ by applying a high voltage across a low pressure in a tube, electrons pass through the gas and collide with gas atoms transferring energy to them. Electrons from the gas _____ move from ground to an excited state and then _____ energy as light as they return to a lower energy state.- Absorption spectrum

- A cool gas that does not emit light will _________ light at characteristic wavelengths (same wavelengths that it would emit if it was giving off light)- Continuous spectrum

- White ____________________ light forms continuous bands of color (red-violet)

- Applications

- determine composition of stars.- used in ________________ to determine composition of samples.- __________ _________ to determine the movement of stars and

galaxies (red shift – blue shift)

*Types of Light1. Incandescent light – a filament is heated to white hot. The hot filament emits __________ and _________ but mostly heat.

- Examples: Light bulbs in lamps/heat lamps- Give off soft _________ glow

2. Fluorescent light – high voltage ___________ energizes atoms in a gas with a diffuse spark (like lightning)

- produces higher frequency light than ___________- not much energy lost as heat therefore more efficient

3. Neon light – electricity passes through a tube containing a gas. The color depends on the _______ in the tube.

4. Black light – UV light is ____________. It is absorbed and re-emitted as visible light.

- Document inspector- Forensic scientist- Hair line cracks in air craft- Find scorpions

5. Laser light – light amplification by _____________ emission of radiation- Monochromatic = _____ wavelength- Collimated = ________ not spread out- Coherent = remain ____ __________

*Brightness(Intensity)- Decreased by the _________ of the distance from the source – Inverse Square Law.- Less light falls on each unit square as the distance of the source increases.- Determines __________ and __________ seasons.

*Wave Nature of Light- Thomas Young’s Experiment – Double slit diffraction

- Diffraction of light through 2 slits which produced an ___________ pattern.- Proved wave nature of light and determined the wavelengths of visible light.

* Polarization – the process of transforming un-polarized to polarized light

- Un-polarized light – vibrates in several ________.- ____________ light vibrates in only one plane.

* 4 Methods of Polarization1. Transmission through a filter which ________ only light in 1 plane to pass. __________ filters block out ½ of the total light.

2. Reflection – non metallic surfaces polarize light parallel to their surfaces (i.e. lake, asphalt, snow)

3. Refraction – un-polarized light may separate into ____ components (vertical and __________)

4. Scattering – light ____________and remitted by atoms, then strike other atoms with the same natural frequency. Scatters and partially polarizes light.

- Contributes to the __________ of the sky and glares in the sky.

*Light and Matter- Luminous body – emit light waves(sun, light bulb)- Illuminated body - _________ light waves (moon)- Transparent – transmits light readily (air, glass)- Translucent – transmits light with __________(frosted glass)- Opaque – does not ________ light (absorbed or reflected – door)

*Color of Light- Eye – three color sensitive neurons called cones

- Red cones: ____________________- Blue cones: ____________________- Green cones: __________________- We distinguish colors by the ratio of cones being stimulated.

- Color of opaque __________ is due to which colors are reflected from the object.

- _______ objects absorb all colors.- _______ objects reflect all colors.

- Primary Light Colors - _________, ______, and _______. Combine to form white light- Secondary Light Colors - __________, _______, and ___________. Produced by combining 2 primary colors- Complimentary colors – 2 colors that add to produce _________ light. (i.e. yellow which is made up of the 2 primary colors _____ and green + ______)

- Red and Cyan (______ & ______) = white- Green and Magenta (______& ______) = white

- Blue and Yellow (______ & ______) = white- Color Addition – mixing of colors of light (_____, _________, _____)

- Uses – TV screens, computer monitors, stage lightingPrimary Colors of Light Color Addition Secondary Colors of LightRed MagentaBlue YellowGreen Cyan

- Dye – molecules that absorb certain wavelengths of light and transmit or reflect others (dye in _______ reflect red, but absorb blue and green light)- Pigment – like dye but larger than a _______(may be seen with microscope). Absorbs certain colors while ___________ others. Often finely ground inorganic compounds (i.e. titanium (IV) oxide – white, chromium (III) oxide - green, carbon – black)- Filters – material which allows only certain colors of light to pass through. (i.e. ___________ _____________, sunglasses*Color Formation by Subtraction – pigments, filters, and dyes absorb certain colors from white light.Primary Pigments Absorbs Reflects – 2 colorsYellow blueCyan redMagenta green

Secondary Pigments Absorbs Reflects – 1 colorRed green and blueBlue red and green

Green red and blue

Note: primary pigments = ____________ ______ _________, and secondary pigments = ____________ _________ __________