Review ReflectionReview Reflection

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Topic 3 RefractionTopic 3 Refraction

Essential Learning OutcomeEssential Learning Outcome

I can describe the refraction of light I can describe the refraction of light through different materials.through different materials.

Law of RefractionLaw of Refraction

The The Law of RefractionLaw of Refraction states that when light states that when light travels from one medium, to a travels from one medium, to a more densemore dense medium, medium, the light will be bent toward the the light will be bent toward the normalnormal, and when it exits the denser , and when it exits the denser medium into a medium into a less denseless dense medium medium it will it will bend away from the normalbend away from the normal.  . 

The new direction of light is called the The new direction of light is called the angle angle of refractionof refraction..

Refraction can also occur when light travels through air at Refraction can also occur when light travels through air at different temperatures, because different temperatures, because warm air is less dense than warm air is less dense than

cold air.cold air.  The refraction of light through air is called a   The refraction of light through air is called a miragemirage.  .  

The pools of water you see on a hot summer day are often caused by this effect, because the air closer to the ground is hotter than the air above it.  As you approach these pools, they disappear - because they were never there.

To understand how a mirage forms, one must To understand how a mirage forms, one must first understand how light travels through first understand how light travels through air. If the air is all the same temperature--air. If the air is all the same temperature--cold or hot--light travels through it in a cold or hot--light travels through it in a straight line. If a steady temperature straight line. If a steady temperature gradient exists, however, light will follow a gradient exists, however, light will follow a curved path toward the cooler air. The curved path toward the cooler air. The standard freshman physics explanation for standard freshman physics explanation for this phenomenon is that cold air has a higher this phenomenon is that cold air has a higher index of refraction than warm air does. As a index of refraction than warm air does. As a result, photons (particles of light) travel result, photons (particles of light) travel through hot air faster than they can through through hot air faster than they can through cold air because the hot air is less dense. cold air because the hot air is less dense.

Is That All There Is To Light?Is That All There Is To Light?

What happens when light strikes a surface? ......What happens when light strikes a surface? ......

Type of Type of behaviorbehavior

What happens What happens to light striking to light striking a surfacea surface

Nature of Nature of surfacesurface

What else What else happens?happens?

AbsorptioAbsorptionn

Energy Energy Transformation Transformation

rough, dark, rough, dark, opaque opaque

some light is some light is reflected reflected

ReflectionReflection Bounces off Bounces off smooth, shiny smooth, shiny some light is some light is absorbed absorbed

RefractionRefraction Travels through in a Travels through in a new direction new direction

different different transparent transparent medium medium

some light is some light is reflected reflected

Refraction DiagramRefraction Diagram

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Refraction DiagramRefraction Diagram

Angles are measured Angles are measured withwithrespect to the line respect to the line which is perpendicular which is perpendicular to the interface.to the interface.

When light travels from When light travels from one medium--such as one medium--such as air, to another one of air, to another one of higherhigherdensity--such as water,density--such as water,usually the light ray usually the light ray bends bends towardtoward the the perpendicularperpendicularline. line.

Important TermsImportant TermsRefractionRefraction – the bending of light when it travels from one – the bending of light when it travels from one

medium (material) to anothermedium (material) to another

Bending LightBending LightWhen light travels into aWhen light travels into a more dense material, light more dense material, light bends bends

toward the normaltoward the normal when light travels into a when light travels into a less dense less dense material, light bends away from the normalmaterial, light bends away from the normal

Temperature can also bend light Temperature can also bend light warm air is less dense warm air is less dense than coldthan cold

Angle of refraction – Angle of refraction – the angle between the normal & the the angle between the normal & the refracted rayrefracted ray

When light strikes a surface it can be absorbed, reflected, When light strikes a surface it can be absorbed, reflected, refracted or a combination of all three.refracted or a combination of all three.

One side of wave front slows One side of wave front slows down, and the entire train down, and the entire train of fronts twists. of fronts twists.

Understanding RefractionUnderstanding Refraction