BELL-RINGER 1. Do a quick evaluation of your comprehension of waves. (write it down) 2. You have three minutes to write as much as you can about waves. (sound & light ok, too!)

BELL-RINGER KEY WORDS Transverse Longitudinal Wavelength Amplitude Frequency Pitch Wave speed Reflection Refraction Diffraction Refraction Interference Beats Intensity Doppler effect EM wave EM spectrum Spherical model

LIGHT IS A WAVE Light exhibits certain behaviors which are characteristic of any wave and would be difficult to explain with a pure particle-view. Light reflects in the same manner that any wave would reflect.reflects Light refracts in the same manner that any wave would refract. refracts Light diffracts in the same manner that any wave would diffract.diffracts Light undergoes interference in the same manner that any wave would interfere.interference And light exhibits the Doppler effect just as any wave would exhibitthe Doppler effect

Objectives Identify the components of the electromagnetic spectrum. Calculate the frequency or wavelength of electromagnetic radiation. Recognize that light has a finite speed. Describe how the brightness of a light source is affected by distance.

Electromagnetic Waves An electromagnetic wave is a wave that consists of oscillating electric and magnetic fields, which radiate outward from the source at the speed of light. Light is a form of electromagnetic radiation. The electromagnetic spectrum includes more than visible light.

ELECTROMAGNETIC SPECTRUM 10e-7

Electromagnetic Waves Electromagnetic waves vary depending on frequency and wavelength. All electromagnetic waves move at the speed of light. The speed of light, c, equals c = 3.00  10 8 m/s Wave Speed Equation c = f speed of light = frequency  wavelength

Electromagnetic Waves Waves can be approximated as rays. This approach to analyzing waves is called Huygens’ principle. Lines drawn tangent to the crest (or trough) of a wave are called wave fronts. In the ray approximation, lines, called rays, are drawn perpendicular to the wave front.

Electromagnetic Waves Illuminance decreases as the square of the distance from the source. The rate at which light is emitted from a source is called the luminous flux and is measured in lumens (lm).

Objectives Distinguish between specular and diffuse reflection of light. Apply the law of reflection for flat mirrors. Describe the nature of images formed by flat mirrors.

Reflection of Light Reflection is the change in direction of an electromagnetic wave at a surface that causes it to move away from the surface. *sports-light behaves like bouncing ball The texture of a surface affects how it reflects light. Diffuse reflection is reflection from a rough, texture surface such as paper or unpolished wood. Specular reflection is reflection from a smooth, shiny surface such as a mirror or a water surface.

Reflection of Light The angle of incidence is the the angle between a ray that strikes a surface and the line perpendicular to that surface at the point of contact. The angle of reflection is the angle formed by the line perpendicular to a surface and the direction in which a reflected ray moves. Law of Reflection: The angle of incidence and the angle of reflection are always equal.

Flat Mirrors virtual image - formed by rays that appear to come from the image point behind the mirror—but never really do. Flat mirrors form virtual images that are the same distance from the mirror’s surface as the object is. A virtual image can never be displayed on a physical surface.

Image Formation by a Flat Mirror

CONCAVE MIRROR - Make-up/shaving mirror; spoon

CONVEX MIRRORS - security mirrors in stores

REFRACTION Refraction - change in direction of a wave due to change in speed at the boundary between two different media. The light ray will not change its direction if it travels along the normal.

DIAGRAM

REFRACTION C:\Projects\Holt-Rinehart- Winston\HRWScience\HRWScience\Holt_Physics\Ch 14\70379.html C:\Projects\Holt-Rinehart- Winston\HRWScience\HRWScience\Holt_Physics\Ch 14\70379.html

REFRACTION Inside of mediums, such as air, glass, or water, the speed of light is usually less than c. c=3.00X10 8 m/s What determines the amount that light bends? Index of refraction - ratio of the speed of light in a vacuum to the speed of light in that substance. Angle of refraction – The angle between the refracted ray and the normal line.

Index of Refraction

Light bends towards the normal when going from lower to higher density material. (air to glass) Light bends away from the normal when going from higher to lower density material. (glass to air)

Lower density – higher density *wavelength decreases, speed decreases *smaller n to larger n Higher density – lower density *wavelength increases, speed increases *larger n to smaller n

Objects appear to be in different positions due to refraction. Snell’s Law determines the angle of refraction.

QOTD: Give an example of refraction and explain…

SNELL’S LAW Snell’s Law A light ray of wavelength 589 nm (produced by a sodium lamp) traveling through air strikes a smooth, flat slab of crown glass at an angle of 30.0º to the normal. Find the angle of refraction,  r. (ANS: 19.2 degrees)

Snell’s Law n 1 sin0 1 =n 2 sin0 2 n 2 /n 1 => Relative Index of Refraction C=n 2 v 2 ___

Total Internal Reflection Total internal reflection can occur when light moves along a path from a medium with a higher index of refraction to one with a lower index of refraction. At the critical angle, refracted light makes an angle of 90º with the normal. Above the critical angle, total internal reflection occurs and light is completely reflected within a substance. Snell’s law can be used to find the critical angle.

Chapter 14 Total Internal Reflection Section 3 Optical Phenomena

Total Internal Reflection

Total internal reflection occurs only if the index of refraction of the first medium is greater than the index of refraction of the second medium. Speed of Light...caught on camera

Applications QOTD: How would life be different if light did not refract? (list three things)

QOTD What do polarized lenses do for you?

Light is a Transverse Wave

Polarization of Light

Polarization of Light Waves Linear polarization is the alignment of electro- magnetic waves in such a way that the vibrations of the electric fields in each of the waves are parallel to each other. Light can be linearly polarized through transmission. The line along which light is polarized is called the transmission axis of that substance.

Linearly Polarized Light

Aligned and Crossed Polarizing Filters Aligned FiltersCrossed Filters

Polarization by Reflection and Scattering Light can be polarized by reflection and scattering. Scattering- waves are dispersed or “sent” in all directions. At a particular angle, reflected light is polarized horizontally. The sunlight scattered by air molecules is polarized for an observer on Earth’s surface.

QOTD Why is a green shirt green?

Definitions: Electrons have a natural, vibrational frequency. Absorption- when incident light frequency matches natural frequency of a material. *Pigments- chemicals capable of selective absorption. Reflection- incident frequency not accepted…light is turned away. For transparent materials: 1. Absorption – matching frequency 2. Transmission – frequency not accepted…light wave is passed through material.

COLOR BY REFLECTION

QOTD Why is the sky blue? Why is the sunset red, pink, and sometimes orange?

Refraction by wavelength

Blue Skies and Red Sunsets

COLOR BY TRANSMISSION

COLOR ADDITION R + G = Y R + B = M G + B = C Animation

QOTD What causes a rainbow to appear and always in the same order?

Dispersion Dispersion-separating polychromatic light into its component wavelengths. White light passed through a prism produces a visible spectrum through dispersion.

QOTD Ever been driving down the road on a hot day when you notice a puddle in the road…but wait…you get closer and the puddle disappears! What’s up with that…what happened?

Atmospheric Refraction Refracted light can create a mirage. A mirage - produced by the bending of light rays in the atmosphere where there are large temperature differences between the ground and the air.

Is it a mirage…or is it a hallucination?

One More Reason Why Physics is Better Than Drugs