LIGHT

Key Points for today What are E-M Waves? Where does light fit in to all of this? Comparing λ and f for different E-M waves Reading quiz next day (16.1)

Just another wave……. Albeit a special kind of wave! Light is an ________________ wave. This means that no medium (water, air, your desk) is needed for the wave to travel.

Albert Einstein

LIGHT: What Is It? Light Energy –Atoms As atoms absorb energy, electrons jump out to a higher energy level. Electrons release light when falling down to the lower energy level. –Photons - bundles/packets of energy released when the electrons fall. Light: Stream of Photons © 2000 Microsoft Clip Gallery

Transverse Waves Energy is perpendicular to direction of motion Moving photon creates electric & magnetic field –Light has BOTH Electric & Magnetic fields at right angles! © 2000 Microsoft Clip Gallery

Electromagnetic (E-M) Waves The light we see is only a small part of the E-M spectrum

Electromagnetic Spectrum © 2000 Microsoft Clip Gallery

Electromagnetic Spectrum Visible Spectrum – Light we can see –Roy G. Biv – Acronym for Red, Orange, Yellow, Green, Blue, Indigo, & Violet. –Largest to Smallest Wavelength.

Questions How long are Radio waves? (give a range) –This distance is approximately equal to _____ –These E-M waves have more / less energy than X-Rays

Electromagnetic Spectrum Invisible Spectrum –Radio Waves Def. – Longest wavelength & lowest frequency. Uses – Radio & T.V. broadcasting. © 2000 Microsoft Clip Gallery

Modulating Radio Waves Modulation - variation of amplitude or frequency when waves are broadcast –AM – amplitude modulation Carries audio for T.V. Broadcasts Longer wavelength so can bend around hills –FM – frequency modulation Carries video for T.V. Broadcasts © 2000 Microsoft Clip Gallery

Electromagnetic Spectrum Invisible Spectrum (Cont.) –X-Rays Def. - EM waves that are shorter than UV rays. Uses: Medicine – Bones absorb x-rays; soft tissue does not. Lead absorbs X-rays.

Electromagnetic Spectrum Invisible spectrum (cont.) –Gamma rays Def. Highest frequency EM waves; Shortest wavelength. They come from outer space. Uses: cancer treatment.

LIGHT: Particles or Waves? Wave Model of Light –Explains most properties of light Particle Theory of Light –Photoelectric Effect – Photons of light produce free electrons © 2000 Microsoft Clip Gallery

Intro to Velocity To find out how fast an object is moving, we need two things: 1.Distance 2.Time velocity = distance/time v = d/t

Man….those things move fast (Pg. 331) How far is it across Earth’s orbit? How much time does it take light to travel across Earth’s orbit?

TO DO….. Read P. 330 – 336 Do “Notes on Light” – Page 1 Do: Practice Problems (1 - 10) in Chapter 16