Light and the EM Spectrum In this unit: 1)Properties of light 2)Reflection 3)Colours 4)Refraction 5)Electromagnetic Spectrum.

Light and the EM Light and the EM SpectrumSpectrum

In this unit:

1) Properties of light2) Reflection3) Colours4) Refraction5) Electromagnetic Spectrum

Part 1 – Properties of Part 1 – Properties of LightLight

Light travels in straight lines:

Laser

Light travels VERY FAST – around 300,000 kilometres per second.

At this speed it can go around the world 8 times in one second.

Light travels much faster than sound. For example:

1) Thunder and lightning start at the same time, but we will see the lightning first.

2) When a starting pistol is fired we see the smoke first and then hear the bang.

We see things because they reflect light into our eyes:

Homework

Luminous and non-luminous objects

A luminous object is one that produces light.

A non-luminous object is one that reflects light.

Luminous objects Reflectors

Shadows

Shadows are places where light is “blocked”:

Rays of light

Properties of Light Properties of Light summarysummary

1) Light travels in ________ lines2) Light travels much _______ than

sound3) We see things because they

________ light into our eyes4) ________ objects make light.5) _________ are formed when light is

blocked by an object

Part 2 - ReflectionPart 2 - ReflectionReflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection

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

The same !

!!

Regular vs. Diffuse ReflectionRegular vs. Diffuse Reflection

Smooth, shiny surfaces have a regular reflection:

Rough, dull surfaces have a diffuse reflection.

Diffuse reflection is when light is scattered in different directions

RefractionRefractionRefraction is when waves _______ or slow down due to travelling in a different __________. A medium is something that waves will travel through. When a pen is placed in water it looks like it is _______

In this case the light rays are slowed down by the water and are bent causing the pen to look odd. The two mediums in this example are ______ and _______.

Words – speed up, water, air, bent, medium

Were you paying Were you paying attention?attention?

1. What is the angle of incidence?

2. What is the angle of reflection?

3. What is, “the law of reflection”?

Were you paying Were you paying attention? cont.attention? cont.

4. Why do things look dull?

5. Why do things look shiny?

6. Why does it look like a pencil is bent if you stick it in water?

7. When light moves from air to water it ______ ________ causing the light to bend. What’s that called?

ColorColor

White light is not a single color; it is made up of a mixture of the seven colors of the rainbow.

We can demonstrate this by splitting white light with a prism:

This is how rainbows are formed: sunlight is “split up” by raindrops.

The colors of the rainbow:The colors of the rainbow:

RedOrangeYellowGreenBlue

IndigoViolet

Adding colorsAdding colorsWhite light can be split up to make separate

colors. These colors can be added together again.

The primary colors of light are red, blue and green:Adding blue and

red makes magenta (purple)

Adding blue and green makes cyan

(light blue)

Adding all three makes white again

Adding red and green makes yellow

Seeing colorSeeing colorThe color an object appears depends on the

colors of light it reflects.

For example, a red book only reflects red light:

White

light

Only red light is

reflected

A white hat would reflect all seven colours:

A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and

blue):

Purple light

White

light

Using colored lightUsing colored light

If we look at a colored object in colored light we see something different. For example, consider a football kit:

White

light

Shorts look blue

Shirt looks red

In different colors of light this kit would look different:

Red

lightShirt looks red

Shorts look black

Blue

light

Shirt looks black

Shorts look blue

Were you paying Were you paying attention?attention?

1. What would we see if all things absorbed light?

2. What would we see if all things reflected all colors of light?

3. Why does a Dodger hat look blue?

4. What colors are not reflected by the Dodger hat?

The Electromagnetic The Electromagnetic SpectrumSpectrum

The light that allows us to see is an electromagnetic wave.

A wave is any disturbance that transmits energy through matter or space.

As a wave travels, its energy causes matter to move.

Energy is carried away from its source by a wave.

Energy TransferEnergy Transfer• Some waves transfer energy through the

vibration of the particles in a medium.

• A medium is a substance through which a wave can travel (can be a solid, liquid, or gas).

• Waves that require a medium are called mechanical waves. Examples are: water waves, sound waves, and seismic waves.

Electromagnetic WavesElectromagnetic Waves

• Visible light can be transferred without traveling through a medium (some kind of matter: water, air, a solid, etc).

• Electromagnetic waves do not require a medium. Some examples are: microwaves; radio waves, which transmit TV and radio signals; and X-rays, which are used by dentists and doctors.

• EM Waves can travel through air, water, and glass. They travel fastest through empty space. And sometimes through YOU!

Were you paying Were you paying attention?attention?

1. What is a wave?

2. Waves that require a medium to move through are called? __________ ___________

3. What are some examples of these kinds of waves?

4. What EM waves are approximately the same length as a bee? ________ ________

5. What EM waves are approximately the same length as the nucleus of an atom? ________ _________

What Makes EM Waves?What Makes EM Waves?•Energy that is emitted (sent out)

from vibrating electric charges produces electromagnetic waves.

• Power waves, radio/TV waves, and microwaves are produced by atoms or molecules vibrating slowly over macroscopic (large) distances.

• Infrared waves are produced by more rapidly vibrating atoms or molecules or by slowly vibrating electrons.

• Electrons vibrating at a faster rate produce visible light.

• Even more rapidly vibrating electrons produce ultraviolet and X-rays.

• Gamma rays are produced by nuclear transitions (changes of the nucleus from one energy level to another).

It can generally be stated It can generally be stated that the more massive the that the more massive the particle, the more slowly it particle, the more slowly it

vibrates. vibrates. • Therefore only tiny masses, such as

electrons, can vibrate fast enough to produce high frequencies, whereas large masses, such as atoms and molecules, vibrate slowly enough to produce low frequencies

• The faster an object vibrates, the more energy it can release.

Were you paying Were you paying attention?attention?

1. EM waves are made by?

2. As particles get smaller and vibrate faster they create waves with _________ wavelengths and higher __________.

3. Which EM waves are produced by the largest and slowest vibrating particles?

________ _________ How do you know?

Lightening Speed…Lightening Speed…All electromagnetic waves travel as fast as

light.Light and EM Waves travel at a speed of

300,000,000 m/s (or meters per second). About 186,000 miles per second.

The wavelength of a wave is the distance between one point on a wave and the corresponding point on an adjacent wave.

The frequency of a wave is the number of waves produced in a given amt. of time.

Waves with SHORT WAVELENGTHS AND HIGH FREQUENCIES carry more energy than waves with LONG WAVELENGTHS AND LOW FREQUENCIES.

X-Rays carry more energy than Radio Waves.

Visible LightVisible LightDef. = The narrow range of wavelengths

and frequencies that humans can SEE! We see different wavelengths as different

colors.Red light = longest wavelengthsViolet light = shortest wavelengths

(carries most energy)Visible Spectrum is the range of colors

that makes up visible light (“Roy G. Biv”)

White Light and White Light and Ultraviolet LightUltraviolet Light

White light occurs when all the colors of visible light are combined. Examples are sunlight and light from light bulbs.

Ultraviolet (UV light) makes up about 10% of the sun’s energy.

UV light carries more energy than visible light.Pros=UV light kills bacteria on food and surgical

instrumentsCons= Skin cancer, wrinkles

Were you paying Were you paying attention?attention?

1. If a wave has a short wavelength it will have a _________ frequency.

2. Which waves have more energy than visible light waves? (hint: Don’t stop at just one.)

3. Which color light has the lowest energy?_________ How do you know?

Were you paying Were you paying attention?attention?

Cont.Cont.1. Approximately how fast does light travel

in space?

2. Which is faster radio waves or ultraviolet waves?

3. Why should you wear sunscreen if you will be out in the sun for a while?

Light and the EyeLight and the Eye

How we use light to see.How we use light to see.Special cells in the back of our eyes can

detect a small range of EM waves called visible light.

These waves are brought into our eye and focused on the back wall by a lens.

The cells react and send signals through nerve cells to our brain where a picture is made.

You will learn more about how the eye works next time.