Where do Where do we get we get light?light?

A luminous object is one that produces light.

An illuminated object is one that reflects light.

Luminous Objects Illuminated Objects

Luminous and Luminous and Illuminated ObjectsIlluminated Objects

We see things because they reflect light into our eyes:

Homework

How does light behave?How does light behave?

ReflectionReflection of Light of Light• Reflection occurs when a

wave bounces back after striking a barrier.

• Example: a reflection in a mirror.

Three things that affect how Three things that affect how light is reflected:light is reflected:

• Surface of the Object

• Color of the Object

• Shape of the Object

Clear vs. Diffuse Clear vs. Diffuse ReflectionReflection

Smooth, shiny surfaces have a clear reflection:

Rough, dull surfaces have a diffuse reflection.

Diffuse reflection is when light is scattered in different directions

Surface of the Object

Ever notice that an asphalt driveway seems hotter on a summer day than a concrete sidewalk?

This occurs because light that is not reflected from the surface of an object may be absorbed by the object and converted into thermal energy.

Color of the Object

Shape Shape of the Objectof the ObjectReflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

The Law of ReflectionThe Law of ReflectionAngle of incidence = Angle of reflectionAngle of incidence = Angle of reflection

In other words, light gets reflected from a surface at ____ _____ angle it hits it.

The same !!!

Types of MirrorsTypes of MirrorsPlane (flat), Concave, & Convex

Plane MirrorsPlane Mirrors• Flat Surface• Light is

reflected straight back, resulting in an upright image that is the same size as the original object.

•Mirror LabMirror Lab

• Read and follow directions for Flip-Flopped Messages to investigate plane mirrors.

• When Completed create a five word message for a partner using the mirrors.

• Have partner decodes.• Using mirrors is fun. • Justify the Law of Reflection Using the plane mirror.

HINT: Think about angles….

Concave MirrorsConcave Mirrors• Curves Inward (like

the inside of a bowl)• If an object is very

close to the mirror, light is reflected in a way that an enlarged, upright image is produced.

• If the object is very far away, the image is reduced in size and upside down.

Convex MirrorsConvex Mirrors• Curves Outward• Results in an image

your eyes detect as upright and reduced in size.

• The side mirrors on cars are convex mirrors. (Objects in mirror are closer than they appear.)

SpoonsSpoonsSteps:1.  Look at your reflection on the inside of the spoon.

Record what you see.The surface on the inside of a spoon bends in like a cave - it is

concave. Dentist use concave mirrors to examine your teeth.  These mirrors

make your teeth look bigger so the dentist can examine them more easily.  Likewise, shaving mirrors are concave because they make the face look bigger.

2.  Now turn your spoon out and look at your reflection on the outside of the spoon. Record what you see.

The surface on the outside of a spoon bends out - it is convex.The next time you are at a funfair take a look at yourself in the crazy

mirrors.  They bend in all sorts of ways so that you look bigger, smaller, fatter, thinner and even wavy.

3. Explain why you look different and how these things pertain to the standard: describe the behavior of light waves Be prepared to report out.

4. Give examples of what we use every day in our daily lives?{Hint} With this understanding of convex and concave mirrors.

RefractionRefraction of Light of Light• Refraction is

the bending of a wave as it passes from one medium to another.

What causes the light to bend?What causes the light to bend?What’s different about air and water?DENSITY – the amount of mass in a certain

volume of a substance (mass/volume)

AIR WATER

gas liquid

Example of RefractionExample of RefractionWhen a straw is placed in water it looks like this:In this case the light rays are slowed down by the water and are bent, causing the straw to look broken. The two mediums in this example are air and water.

Another Example:Another Example:When you use a

magnifying glass, the object appears larger because of refraction.

The light waves traveling in the air change direction when they enter the glass of the lens, and then again when they move from the glass back into the air again.

Lens

Introduction of Magnifying GlassIntroduction of Magnifying GlassI bumped into this week's experiment while washing the dishes.

Lisa had placed a new cartridge for our water filter into a glass of water to rinse it. When I glanced up, the filter had swollen until it filled the inside of the glass! It was only when I lifted the normal sized filter out of the glass that I realized what had tricked me. To investigate, you will need: a tall, clear drinking glass water your finger, a spoon, a banana, etc.

Place the glass on a flat surface. Looking from the side, stick your finger into the glass. OK, nothing unusual so far. Now fill the glass with water. Again, stick your finger into the glass. Looking from the side, this time you should see a difference. Your finger looks bigger. Try the same thing with a large spoon. An object that is about half as wide as the glass will seem to fill it. Why?

The glass of water acts as a lens to magnify objects inside. The thin layer of glass alone does not cause the magnification. You need the water for it to work. Without the water, light enters the glass and hits your finger. Some of the light is absorbed, and some is reflected, spreading outwards. Some of this light hits your eye and you see your finger.

With water in the glass, things start the same. Light still reflects from your finger and spreads outwards. This time as the light moves from the water to the glass and then to the air, something happens. Its speed changes. Wait a minute! The speed of light is a constant, right? 300,000 k/m per second. That speed is for light in a vacuum. It travels through other substances (air, water, glass, oil) at different speeds. As it changes speed, if it is traveling perpendicular to the surface (straight through), nothing much happens. If the boundary is at an angle to the direction the light is traveling, the light is bent from its path.

The shape of the surface at the speed change also has an impact on what you see. If the boundary between two different substances is flat, then you don't notice much of a difference. The image may be shifted to the side as the light is bent, but everything looks the right size. If the boundary is curved, then the image is distorted. Depending on the shape of the boundary and the speed of light in each of the substances, the light waves can be spread apart or bent together. If they are spread outwards, the image looks bigger. If they are bent inwards, the image looks smaller.

This has other implications besides making fingers look larger. Would a lens shaped to focus light on Earth (in air) work the same in space? If you wear eye glasses, do you think they would work well if you were underwater? For that matter, do your eyes work as well underwater as in air? What would you see if you were in a room filled with water and you stuck your finger into a glass of air?

DiffractionDiffraction of Light of LightDiffraction is

the bending, spreading, and interference of waves when they go through a narrow opening.

Diffraction PatternsDiffraction Patterns

• Radio waves can diffract around hills, mountains or even the whole planet.

• Light waves can diffract through tiny slits.

• X-rays can diffract around atoms.

Electromagnetic waves have a Electromagnetic waves have a huge range of wavelengths.huge range of wavelengths.

If the wavelength is of a similar size to a gap in a harbor wall, then the wave will diffract as shown below.

If the wavelength does not match the size of the gap, then only a little diffraction will occur at the edge of the wave.

TransmissionTransmission of Light of Light

Transmission is the passing of waves through a medium.

Safety Rules for lights and Safety Rules for lights and PrismPrism

Lights out of eyesHandle objects with carehttp://www.youtube.com/watch?v=NU2r-ECmPr4

http://www.youtube.com/watch?v=NU2r-ECmPr4

Prism LabPrism LabSeparating light with a prism experiment   Try It Out Inside the box, place the prism on a sheet of dark

paper. Shine the flashlight beam through the hole and adjust the prism as shown in the diagram. Use coloured pencils or pens to trace the individual bands of light that you see. In what order are the colours? Can you come up with a mnemonic to help you memorise the sequence of colours in prismatic light?       

Make ItIn order to create a clearly visible spectrum of light with a prism, it's best to work in a darkened room with a single source of light. A cardboard box (such as a file box) makes a great prism box. Simply cut a small rectangular opening on the side of the box near the bottom edge, about 5 mm in width. 

Experiment Finally, cut a second hole in the box and arrange two prisms so that

their spectra cross paths. What happens to the various colours of light where they cross?    You will need:

· A prism (or two) · A cardboard box (such as a file box) · Coloured pencils or pens · A sheet of plain white paper · A flashlight or reading lamp         

 

Questions for Written ReportQuestions for Written ReportDiscuss visible light spectrum:• Explain why does the prism make the spectrum• How do you make the spectrum narrow or wide?• When adding double plane mirrors with a prism,

describe what happens with the visible light spectrum?

• Synthesis the two types of light concepts used when there are prisms and mirrors in the experiment.

• Consider a (What if question) using the prisms and mirrors then analyze your response.

Be prepared to Report out your Lab findings and how they relate to the standard.

S8P4a,bCharaacteristics of the E/M Spectrum; describe the behavior of light waves

What happens when light What happens when light hits these objects?hits these objects?

•Glass of water •School bus window•Notebook paper•Waxed paper•Plastic wrap•Tissue paper•Cardboard•Textbook•Hand lens…

Many materials are classified by Many materials are classified by how well they transmit light.how well they transmit light.

• Three Types of Materials:– Transparent– Translucent– Opaque

TransparentTransparentA material

that permits light to pass through

Transparent objects:Transparent objects:

– The windows on a school bus,– A clear empty glass,– A clear window pane,– The lenses of some eyeglasses,– Clear plastic wrap,– The glass on a clock,– A hand lens,– Colored glass…

•ALL of these are transparent. •Yes, we can see through them because light passes through each of them.

TranslucentTranslucentA material that

transmits some light but also scatter light in all directions

Translucent objects:Translucent objects:– Thin tissue paper,– Waxed paper,– Tinted car windows,– Frosted glass,– Clouds,

•All of these materials are translucent and allow some light to pass but the light cannot be clearly seen through.

OpaqueOpaqueA material

that allows no light to pass through

Opaque objects:Opaque objects:– Heavy weight paper,– Cardboard– Aluminum foil,– Mirror, bricks,

buildings,– Your eyelids and hands,– Solid wood door,

•All of these objects are opaque because light cannot pass through them at all.•They cast a dark shadow.

Shadows

Shadows are places where light is “blocked”:

Rays of light

Compare and ContrastCompare and ContrastTransparent objectsTranslucent objects Opaque objects

Explain why each group is the type of material and how they are used in our daily lives.

Be prepared to Report out your answers and how they relate to the standard.

. S8P4a,b describe the behavior of light waves

THANK YouTHANK You