Agenda

• Examine Light• 32.1-32.3

– Qualitative For most part– Light traveling in materials– Existence of E&B fields in light

• 33– Reflection&refraction– Polarization– Dispersion

• Finish by Monday at latest– Explore polarization in lab Tues

Today

• Light in Materials

• Reflection & Refraction

• Trig Fun

Light Meets Matter

Ray of LightThink Beam

Light Meets Matter

Metal?

Ray of LightThink Beam

What Happens?

Metals absorb E-fieldsNo light enters metalSome absorbedSome reflected

I < I0

Light Meets Matter

Non-Metal?

Ray of LightThink Beam

What Happens?

Some entersSome reflectsSome gets absorbedAffects speed by polarization

Reflected + Refracted Intensity < Original

Magic of Trigonometry

• Reflection

• Incident Angle = Reflected Angle

• Measure from Surface Normal

ReflectiveSurface

R

First Thought

• Why are Mirrors Blurry after a shower?

First Thought

• Why are Mirrors Blurry after a shower?

ReflectiveSurface

R

Reflection off flat surface

First Thought

• Why are Mirrors Blurry after a shower?

ReflectiveSurface

R

Reflection off water droplet…

Mirror Trick You can try @Home

• How much of yourself can you see in a mirror?

Mirror

Where does light come from?

• Hand?

Mirror

Where does light come from?

• Feet?

Mirror

Light

Light reflected/emitted from feetAll different anglesOnly one angle bounces off mirror right

Where does light come from?

• Feet?

Mirror

Light

Light reflected/emitted from feetAll different anglesOnly one angle bounces off mirror rightIncident Angle Must Equal Reflected!

Let’s Try a half Height Mirror

• Say you are 6’ Tall, Mirror 3’ Tall, Mirror 5’ Away• How much of yourself can you see?

What is light ray for bottom part?

Let’s Try a half Height Mirror

• Say you are 6’ Tall, Mirror 3’ Tall, Mirror 5’ Away• How much of yourself can you see?

Where does ray come from?

Let’s Try a half Height Mirror

• Say you are 6’ Tall, Mirror 3’ Tall, Mirror 5’ Away• How much of yourself can you see?

Where does ray come from?Find angle…

Let’s Try a half Height Mirror

• Say you are 6’ Tall, Mirror 3’ Tall, Mirror 5’ Away• How much of yourself can you see?

Where does ray come from?Find angle…

Let’s Try a half Height Mirror

• Say you are 6’ Tall, Mirror 3’ Tall, Mirror 5’ Away• How much of yourself can you see?

Where does ray come from?Find angle…tan()=(3/5)

3

5

Let’s Try a half Height Mirror

• Say you are 6’ Tall, Mirror 3’ Tall, Mirror 5’ Away• How much of yourself can you see?

Where does ray come from?Find angle…tan()=(3/5)Where does light come from?

3

5

Let’s Try a half Height Mirror

• Say you are 6’ Tall, Mirror 3’ Tall, Mirror 5’ Away• How much of yourself can you see?

Where does ray come from?Find angle…tan()=(3/5)=tan(R)

3

5

R

Does it Matter How far Away Mirror is?

• Think: Total angle is 2x incident angle

• If mirror is ½ height….– Light at edge travels ½ vertical each way– So makes up 2x height

• Can prove mathematically

• Or just calculate at different distances

• Or look in mirror….

What is angle of reflection?

= 20O

IdeaSolve for #’s, try q=10o, see pattern?

Future

• Friday

• Refraction– More Trig– Dielectric Constant & Index Refraction