Unit 10Waves & Wave Properties

Electromagnetic Waves

Electromagnetic Spectrum“Light Waves”

Electromagnetic Spectrum “Light Waves”• Waves caused by disturbing electric and magnetic

fields, resulting in visible light (which we see), infrared light, x-rays etc…

• Electromagnetic Waves– Do not NEED a medium to travel– Can travel through a vacuum

• Transverse Waves– Vibrations are perpendicular to wave motion.

Electromagnetic Spectrum“Light Waves”

• Light waves can travel through a vacuum• Speed of Light in a vacuum: 300,000,000m/s• Light can also travel through many mediums.• Different parts of the Electromagnetic Spectrum can

penetrate different types of materials (aka: mediums)

• If the light moves through a medium, when the medium changes, the speed of light changes.

• This is called Refraction!

Notice the straw appears to be broken or bent. In reality it is just the bending of the light waves as it travels from one medium to another.

The Speed of Light changes when the medium changes. This results in the “bending” of light.• Refraction: Light bends as it travels from one

medium to another.

Examples of Refraction Due to the change in medium the light bends – making it appear the object in the water is in a different location. Like the means’ body.

You know you have tried endlessly to catch fish or frogs in water … refraction helps explain why it’s more difficult than it may seem!

An oasis is also an example of refraction!•A classic case of Refraction.The road appears wet – the light seems wavey. •A similar appearance to the air above a hot radiator. Why? •Hot air is a different medium than cold or cooler air. Light changes it’s speed as it goes from a hot to cold air and thus the light bends, giving a wavey appearance, which sometimes appears “wet” in our eyes. •This is why people in the desert think they see water in the distance! The air over the hot sand is hotter than the cooler air above and the light bends as it goes though the different mediums!

Electromagnetic Spectrum“Light Waves”

• Parts of the Electromagnetic Spectrum have different properties.• These properties are based on their frequency and wavelength.

f λLow Energy Waves

f λHigh Energy Waves

f λ f λHigh Energy Waves Low Energy Waves

Properties of EM Waves• Radio Waves (Lowest frequency)– Communication (Radio, telephones, television)– GPS (Global Positioning System)

• Microwaves– GPS– Radar– Microwave Ovens

• Infrared Rays– Heat produces infrared light– Night Vision (sees “heat”)

• Visible Light– Red, Orange, Yellow, Green, Blue, Indigo, Violet• ROY G BIV

– Seeing, cameras, telescopes, colors.– White light is a mix of ALL colors.– Black is the absence of light (no light!)

Properties of EM Waves

• Ultraviolet Rays (UV)– High Energy, penetrate your skin.– Sunburn, skin cancer– Used to disinfect medical equipment

• X-Rays– Higher Energy, penetrate your skin, your muscles and tissues.– Can reflect off bones so you can “see” inside your body!

• Gamma Rays (Highest Frequency!)– Can penetrate even through lead/concrete walls!– Highest Energy, penetrates through your body.– From nuclear reactions, very dangerous, can kill, cause cancer.– Also used to treat cancer!

Properties of EM Waves

The Doppler Effect is true for light waves as well!

higher frequency waves (bluer waves)

The frequency changes due to relative motion – this results in seeing…

lower frequency light waves (redder waves)

Doppler Effect – Light Waves

Low frequency is red light.High Frequency is blue light

Doppler Effect – Light Waves

Watch the video “Doppler Effect, Universe Expansion”http://www.hopehsbluewave.org/apps/video/watch.jsp?v=42670 http://youtu.be/h4OnBYrbCjY

(2-3min)

This is what the line spectra for red or blue shift would look like.

Doppler Effect – Light Waves

And this is used to tell if the source is moving toward or away from us and at what speed.

Doppler Effect – Light Waves

Blue Shift – Physics HumorDoppler Effect – Light Waves

How are Rainbows Formed?

Refraction and Dispersion• Refraction: Light

bends as it travels from one medium to another.

• Dispersion: The process of separating polychromatic light into its component wavelengths

Rainbows form due to Refraction and Dispersion

• Refraction is when light bends when it travels from one medium to another. It is known that different wavelengths will bend different amounts.

• The lower the wavelength (higher frequency) the more the light bends. [increase wavelength, decrease frequency, less bending]

• Dispersion is a special case where the light bends such that polychromatic light (like white light) separates into its component wavelengths, each individual color in the case of a rainbow.

• Blue light, with a short wavelength, bends the most, and therefore appears on the bottom of the rainbow.

• Red light, with a long wavelength, bends the least, and appears at the top of the rainbow.

Reflection - Light

Pushing the Learning: Law of Reflection

Reflection – LightReal vs. Virtual Images

Flat Mirror

Flat Mirrors too!

Reflection - Light

Reflection - Light

PolarizationMost light sources produced unpolarized light. These are light waves that vibrate in many directions – while still being a transverse wave.

Polarized light waves are light waves in which the vibrations occur in a single plane.

Unpolarized light.

Light can be polarized by having unpolarized light travel through a filter as shown below

What does “polarization” look like?This is a artists representation of light being polarized.

Polarization is shown below .Sunglasses are a great example of polarization!

Follow the diagram below to see how sunglasses polarize light.

Polarization Example

Double Polarization – not light allowed through!

Superposition Principle - LightHow does interference “look”?