Chapter 26 Properties of Light

Sources of light Luminous –Producing light –The Sun (luminous) versus the Moon (nonluminous) Incandescent –Glowing with visible light from high temperatures –Examples: flames, incandescent light bulbs –Produce light via electromagnetic waves Electrical charge is accelerated by external force Acceleration produces wave consisting of electrical and magnetic fields Wave moves through space; the fields exchange energy and continue on until the energy is absorbed by matter

Fluorescent Lamps Primary excitation - electron collisions with low pressure mercury vapor, and ultraviolet light is given off Secondary excitation - ultraviolet light is absorbed by phosphors and these emit visible light

Phosphorescence Phosphorescence - a type of light emission that is the same as fluorescence except for a delay between excitation and de-excitation. Electrons get "stuck" in an excited state and de-excite gradually. Demos - glow-in-the-dark objects

Lasers Laser –Light amplification by stimulated emission of radiation Lasers produce coherent light. Coherent light means that all the light waves have the frequency, phase and direction. Demo - Laser and chalk dust Demo - Laser and prism or diffraction grating

1. Incandescencea. mercury vapor light tubes 2. Fluorescenceb. glow-in-the-dark paints and plastics 3. Phosphorescencec. light bulbs with filaments

1.Fluorescent Lampa. color changes with temperature 2.Incandescent Bulbb. only one color of light 3. Laserc. converts ultraviolet light to visible light

These three are the same… Light *pure energy Electromagnetic Waves *energy-carrying waves emitted by vibrating electrons Photons *particles of light

Electromagnetic Waves Demo –Tesla Coil, Radio, Fluorescent light

Electromagnetic Wave Velocity The speed of light is the same for all seven forms of light. It is 300,000,000 meters per second or 186,000 miles per second.

The Electromagnetic Spectrum Radio Waves - communication Microwaves - used to cook Infrared - “heat waves” Visible Light - detected by your eyes Ultraviolet - causes sunburns X-rays - penetrates tissue Gamma Rays - most energetic

THE ELECTROMAGNETIC SPECTRUM EM Waves Sources Radio Waves Microwaves Infrared Visible Ultraviolet X-rays Gamma rays Vibrating charges Molecular vibrations Atomic vibrations Nuclear vibrations

The Electromagnetic Spectrum A range of light waves extending in wavelength from radio waves to gamma rays

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

The speed of light... (a) has never been measured (b) is about the same as that of sound (c) is infinitely fast (d) is very fast, but not infinite

Which characteristic of waves of visible light is most similar to waves of microwaves? A)speed B)wavelength C)frequency D)amplitude

Transparent Materials Transparent - the term applied to materials through which light can pass in straight lines

Opaque Materials Opaque - the term applied to materials that absorb light

Shadows Umbra - the darker part of a shadow where all the light is blocked Penumbra - a partial shadow These terms also apply to Solar Eclipses and Lunar Eclipses.

Penumbra Umbra Partial Shadow Full Shadow Solar Eclipse Sun Moon Earth A solar eclipse occurs when the Moon passes in front of the Sun.

Lunar Eclipse Sun Earth Moon A lunar eclipse occurs when the Moon passes into the Earth's shadow.

SEEING LIGHT - THE EYE Cornea -does most of the focusing Iris - Pupil - has the eye color and controls light intensity Lens - the hole in the eye (red eye demo) does remainder of focusing Retina -location of light sensors, has rods and cones Blind spot - Fovea - center of vision, predominantly cones optic nerve exit, no light sensors

Color Deficiency

Myopia (Near-Sightedness) People with near-sightedness cannot see clearly at distance.

Hyperopia (Farsightedness) People with far-sightedness cannot see clearly up close.

The human eye Uses convex lens with muscularly controlled curvature to change focal distance Nearsightedness (myopia) - images form in front of retina Farsightedness (hyperopia) - images form behind retina Correction - lenses (glasses, contacts) used to move images onto retina