Why is the sky blue? Why are clouds white? Why are sunsets red?

Optics ______________is the study of light. Light is a ____________________________________wave. transverse electromagnetic __________– _________________ - _________________ Doppler effect Light can act like a… wave diffraction interference …or like a ______________called a____________ . particle photon (Visible) light is ________________________ . all that you can see

ROYGB(I)V e&m spectrum The electromagnetic ( _____ ) ___________________: spectrum ROYGB(I)V The only differences between the different radiations are their _________________ and/or __________________ . For this reason, the entire ______________________is sometimes referred to simply as ___________________ . frequencies wavelengths e&m spectrum light

Ex. Compare sound and light waves vibration type type of propagation amplitude determines: frequency sound light longitudinal mechanical loudness pitch transverse e&m brightness color Ex: Light waves in a vacuum: C: A: B: D: Which light wave is brighter and blue-er? Which is dimmer and blue-er? Which is brighter and redder? Which is dimmer and redder? D A B C

Ex: Put in order from slowest to fastest in a vacuum: x-rays, blue light, radio waves ________ e&m radiation (light) travels ________________ ________________________: ___________________________. All at the same speed in a vacuum Ex. Find the wavelength of a red light wave.

Ex: Put in order from slowest to fastest in a vacuum: x-rays, blue light, radio waves ________ e&m radiation (light) travels ________________ ________________________: ___________________________. All at the same 3.00 x 108 m/s speed in a vacuum Ex. Find the wavelength of a red light wave. v = fl 3.00 x 108 m/s = ( ??? ) l

Reference Tables, page 2, top: The Electromagnetic Spectrum Are these frequencies or wavelengths? Choose f = 4.0 x 1014 Hz

Ex: Put in order from slowest to fastest in a vacuum: x-rays, blue light, radio waves ________ e&m radiation (light) travels ________________ ________________________: ___________________________. All at the same 3.00 x 108 m/s speed in a vacuum Ex. Find the wavelength of a red light wave. v = fl 3.00 x 108 m/s = ( ??? ) l 3.00 x 108 m/s = l (4.0 x 1014 Hz) 0.75 x 10-6 m = l 7.5 x 10-7 m = l  small  little diffraction, normally

Wavefronts propagating from a source plane wavefronts Spherical wavefronts

________________: A wave in one medium is _____________ on a surface (__________________ ) and returns back ______________________________. Reflection incident boundary into the same medium perfectly smooth Ex. waves incident on a _________________________surface reflected wave incident wave surface

Reflection can be understood using Huygens wavefronts that spread out from each point on the surface as the incident wave arrives: reflected wave incident wave surface

anechoic chambers a(n) = no echoic = echo - very little reflected sound waves…. Why? Each time the sound wave is reflected, it loses some energy.

wavefronts For simplicity, this: direction of motion of wave …will be replaced by this: a “ray” the direction The ray arrow only shows _______________________ of the wave.

qi = qr qi qr Using only rays: incident reflected ray ray normal incident ray reflected ray qi qr surface qi = qr incident angle reflected angle This is called the ___________________________. Law of Reflection with respect to The angle q is always measured _________________ _____________________ . the normal.

In the Physics Reference Tables: page 5

Ex: What is the angle of reflection? Draw the reflected ray. 600 incident reflected 600 600 300 surface Ex: What is the angle of incidence? Draw and label the incident ray. 100 surface 100 incident reflected 100

How does reflection change a wave? reflected: vr, fr, lr incident: vi, fi, li normal surface vi = vr 1. Same medium  _________________ 2. Same color  ________________ 3. Since _____ = v/f,  _____________. As a result, the _______________ wave has the same _______________________ as the incident wave. fi = fr l li = lr reflected v, f and l

The Law of Reflection is _____________true… 1. …for ______ waves: __________ ___________ 2. …and is ______________________ of the v, f or l of the incident wave. This means that all different ________________ of light and _______________ of sound obey the Law. always all light sound earthquake water gravity etc Ex: 400 ________ angle for any ________ surface

Sound waves obey the same Law of Reflection as light. How do they “aim” the sound in these concert halls?

The Law of Reflection is _____________true… 1. …for ______ waves: __________ ___________ 2. …and is ______________________ of the v, f or l of the incident wave. This means that all different ________________ of light and _______________ of sound obey the Law. always all light sound earthquake water gravity etc independent colors pitches Ex: 400 400 same ________ angle for any ________ color surface

Reflecting telescopes: All colors reflect at the same angle and meet at the same focus: white light curved mirror focus white light

Why are some surfaces good _______________? mirrors Why are some surfaces good _______________? Types of reflection: Regular, mirror, specular _____________________________: from smooth, flat surfaces 2. _____________: from rough surfaces diffuse ________ Regular Diffuse

The Law of Reflection is obeyed for_______________ and____________________________. both regular diffuse reflection. Even though the ______________ are in different directions, the incident and reflected _________________ . normals angles are equal

Identify regular and diffuse reflections.

for visible light, whose l is ~ 10-6 to 10-7 m 3 m Liquid Mirror Telescope (LMT). This unique telescope used a pool of mercury spun in a dish at 10 rpm to form the primary mirror. The main limitation of the telescope was that it could only point vertically. The LMT was used to optically measure the low Earth orbit (LEO) debris environment. The telescope was located in Cloudcroft, NM and was closed in 2001. These must be smooth for visible light, whose l is ~ 10-6 to 10-7 m The Hubble mirror.

Why aren’t these telescopes smooth?

Compare radio wavelengths to visible wavelengths: l = 1-103 m l = 10-6-10-7 m To the radio wavelengths, the telescopes "appear" smooth.

Ex: Driving at night: oncoming traffic dry you road: oncoming wet diffuse reflection you rough surface  more diffuse reflection  some light scattered back you see road  less scattered forward  less glare for oncoming oncoming traffic wet road: smooth surface  less diffuse reflection  less light scattered back you can’t see road  more scattered forward  more glare for oncoming traffic

Why is the sky blue? Why are sunsets red?

Water drops and ice crystals of all Why are clouds white? Water drops and ice crystals of all different sizes scatter (reflect) all different wavelengths (frequencies) of light. Why are clouds black? …because they’re dirty!© - in shadow of upper clouds - light cannot penetrate to them. ©SuzieSmithProductions

Why is the ocean greenish-blue? 1. It reflects the sky. 2. It reflect blue wavelengths better than other colors. 3. It absorbs red wavelengths better. Lobsters on the ocean floor appear black because little red light gets down there

Why are Uranus and Neptune green/blue? Methane in their atmospheres absorb orange/red, so the reflected light is the complementary color.

Reflection nebulae – young stars, surrounded by dust that scatter the blue light in our direction.

Ex: Albedo = percentage of incident light that is reflected back from a planet or moon. What is the albedo of the Moon? In other words, of all the sunlight incident on the Moon, what percentage is reflected back? Only 0.07 = 7% on average! out of 100% only 7% on average is reflected back

It seems very bright against a dark sky.

Its brightness is best compared when 1. an "almost full" moon is rising after sunset; or 2. a "just past full" moon is setting at sunrise: white building