Light

The Electromagnetic Connection A changing magnetic field produces an electric field, and a changing electric field produces a magnetic field. Electric and Magnetic fields can produce forces on charges An accelerating charge produces electromagnetic waves (radiation)

Both electric and magnetic fields can transport energy –Electric field energy used in electrical circuits, e.g., released in lightning –Magnetic field carries energy through transformer, for example

Electromagnetic Radiation Interrelated electric and magnetic fields traveling through space All electromagnetic radiation travels at c = 3  10 8 m/s in vacuum – the cosmic speed limit! –real number is m/s exactly

Examples of Electromagnetic Radiation AM and FM radio waves (including TV signals) Cell phone communication links Microwaves Infrared radiation Light X-rays Gamma rays What distinguishes these from one another?

Uses of Electromagnetic Waves Communication systems –One-way and two-way Radar Cooking (with microwaves) Medical Imaging (X rays) “Night Vision” (infrared) Astronomy (radio,  wave, IR, visible, UV, gamma) All that we experience through our eyes is conveyed by electromagnetic radiation…

The Electromagnetic Spectrum Relationship between frequency, speed and wavelength f · = c f is frequency, is wavelength, c is speed of light Different frequencies of electromagnetic radiation are better suited to different purposes The frequency of a radio wave determines its propagation characteristics through various media

Polarization of Radio Waves B E Transmitting antenna

Reception of Radio Waves Receiving antenna works best when ‘tuned’ to the wavelength of the signal, and has proper polarization Electrons in antenna are “jiggled” by passage of electromagnetic wave B E

Questions Why are car radio antennas vertical? Why are cell phone antennas so short? How do polarizing sunglasses work?

Radio waves Radio waves – between 100-1m long Communication, radio and tv AM- amplitude modulation FM Frequency modulation

Microwaves Wavelength between 1m and 1mm long Used for communication, radar and cooking food

Infrared Wavelength between just below visible light Between 750nm and 1mm Perceived as heat Night vision, heating Nanometer is 1/ of a meter

Visible light Color Red Orange Yellow Green Blue Violet Wavelength(nm) Frequency

Spectroscopy spectrometer is an optical instrument used to measure properties of light over a specific portion of the electromagnetic spectrumopticallightelectromagnetic spectrum Elements give off different emission spectra when they glow These can be used to identify the presence of elements

Hydrogen Helium Carbon Nitrogen Oxygen Neon Sodium

Properties of visible light Absorption- light is absorbed by matter Why does your flashlight become dim at a distance Scattering is the release of light by the matter Prism- Refracts light twice, different wavelenghts are refracted more than others

The Visible Spectrum A range of light waves extending in wavelength from about 400 to 700 nanometers.

Things that create a Spectrum Prism Raindrops CD’s Spectroscopes –Contains a Diffraction Grating

Hot gas produces a bright line emission spectrum. (Bright Lines) Emission Spectra

Absorption When an electron is raised to a higher energy level, the atom is said to be excited.

Emission When the electron returns to a lower energy level, energy is released in the form of light.

Transmission Matter that allows visible light to easily pass through are transparent Matter that scatters light is translucent Matter that does not transmit light is called opaque

Ultraviolet Wavelenghts above visible light 400nm- 1nm Photons have enough energy to kill living cells Present in sunlight

X-rays 10 to 0.01 nanometers, nanometers Diagnostic imaging Astronomy

Gamma rays Shorter then.01nm Radioactive decay Great penetrating power

Parts of the Human Eye (Supplement Handout) Cornea – bends light Iris – controls the amount of light Pupil - opening Lens – focuses light onto retina Retina – back of eye Fovea – center of your vision Optic Nerve – “signal wire” (causes blind spot) Blind Spot Demo OX

Rods - brightness receptors Cones - color receptors –T–Three Types: Red, Green, Blue Cones are more numerous in the center of your vision. Rods are more numerous around the periphery of your vision. Demo – Moving markers near periphery

Color Deficiency

Color Vision Colorblindness - about 10% of population Red-green is predominant Yellow-blue - a few

What is color? Different wavelengths of light are perceived as different colors. White light contains equal amounts of these colors. (ROY G. BIV)

Fill in the Blanks Black objects _______ all of the pure colors. White objects _______ all of the pure colors. Transparent objects _______ all of the pure colors. absorb reflect transmit

Mixing Colored Light Color Addition Additive Primary Colors: Red Green Blue One can produce any color by varying amplitude and mixture or red, green and blue light.

Complementary Colors - any two colors that add together to produce white e.g. magenta + green = white

After Images and “Conal Fatigue” The human eye will see complimentary colors after staring at a color picture.

Transparent and Opaque Transparent –you can identify objects through it Translucent –you see diffuse light coming through it Opaque –you cannot see any light coming through it –Opaque objects cast shadows.

The Electromagnetic Spectrum Radio Waves Microwaves Infrared Visible Light Ultraviolet X-rays Gamma Rays Raging Martians Invade Roy G. Biv Using X-rays and Gamma Rays mnemonic

Atmospheric Refraction Our atmosphere can bend light and create distorted images called mirages. Mirage 1.mpg What causes stars to twinkle? –Atmospheric Turbulence

Earth Sun Because of atmospheric refraction, we have lingering, elliptical sunsets.

Holography Holography- technique that produces a 3- D image without a lens

Why is the sky blue? Nitrogen and Oxygen in our atmosphere scatter high frequencies of light.

Why are sunsets red? Red light is scattered the least by our atmosphere. The greatest path of sunlight through the atmosphere is at sunset or sunrise.

Why are clouds white? The color of light scattered by clusters of water molecules vary with the size of the clusters. The size of clusters of water molecules (droplets) vary in clouds.

What happens when the source in in motion? Movie #1 Movie #1 Java

Source in Motion Short Wavelength High Frequency High Pitch Weeeeeeeee!!! Long Wavelength Low Frequency Low Pitch Ooooooo!!! As a team, describe what happens to the wavelength, frequency, and pitch both in front of and behind a moving sound source.

Doppler Effect Examples: –moving cars and trains Sound Movie #2 –moving buzzer in a nerf ball (in class)

The Electromagnetic Spectrum Radio Waves - communication Microwaves - used to cook Infrared - felt as warmth Visible Light - detected by your eyes Ultraviolet - causes sunburns X-rays - penetrates tissue Gamma Rays - most energetic .      .      ROYGBIVROYGBIV Mnemonic? Raging Martians Invade Roy G. Biv Using X-rays and Gamma Rays