Welcome Wednesday! DUE TODAY: PRACTICE 02 – SIMPLE HARMONIC MOTION Pick up the packet titled “Notes 01- Light and the Electromagnetic Spectrum” Grab a calculator Raytheon is coming on Friday….presentations! 3 rd Quarter test – Next Monday Today’s notes are worth a grade

2 Light - The EM Spectrum

What is electromagnetic radiation? A term used to describe all of the different types of energies released into space by stars, like our Sun All electromagnetic radiation (EM radiation) travels in STRAIGHT LINES AND waves EM radiation includes visible light, radio waves, UV rays, microwaves and more Speed of light in a vacuum is 3 x 10 8 m/s All electromagnetic waves travel at the speed of light

4 Spectrum of Electromagnetic Radiation RegionWavelength (Angstroms) Wavelength (centimeters) Frequency (Hz) Energy (eV) Radio> 10 9 > 10< 3 x 10 9 < Microwave x x Infrared x x x Visible x x x x Ultraviolet x x x X-Rays x x Gamma Rays< 0.1< > 3 x > 10 5

Speed of light… 3 x 10 8 m/s or 186,000 miles Per second

6 longershorter lower higher

Remember the following sentence: Radioactive Martians invade Venus using x-ray guns. This sentence shows the order of the types of electromagnetic radiation from lowest frequency and energy to highest frequency and energy. Radioactive – Radio, Martians – Microwave, Invade- infrared, Venus – visible, Using – ultraviolet, x-ray- x-ray, guns- gamma

8 Radio Waves

9 Radio waves bring music to your radio. carry signals for your television and cellular phones. Radio waves are NOT sound waves Radio Waves

10 Radio Telescopes Radio telescopes look at planets and comets, giant clouds of gas and dust, and stars and galaxies. Radio astronomy has the advantage that sunlight, clouds, and rain do not affect observations.

11 Radio Telescopes In order to make better radio images, astronomers often combine several smaller telescopes, or receiving dishes, into an array. Together, the dishes can act as one large telescope

12 Radio Telescopes The Very Large Array (VLA), located in New Mexico, is one of the world's premier astronomical radio observatories. The VLA consists of 27 antennas arranged in a huge "Y" pattern up to 36 km (22 miles) across -- roughly one and a half times the size of Washington, DC.

13 Microwaves Microwaves have wavelengths that can be measured in centimeters

14 Microwaves close to a foot in length are the waves which heat our food in a microwave oven. Microwaves

15 Microwaves are good for transmitting information from one place to another because microwave energy can penetrate haze, light rain and snow, clouds, and smoke. Microwaves This microwave tower can transmit information like telephone calls and computer data from one city to another.

16 Shorter microwaves are used for radar like the doppler radar used in weather forecasts. Microwaves, used for radar, are just a few inches long. Microwaves

17 Radar is an acronym for "radio detection and ranging". Radar was developed to detect objects and determine their range (or position) by transmitting short bursts of microwaves. The strength and origin of "echoes" received from objects that were hit by the microwaves is then recorded. Microwaves

18 The Infrared Infrared light lies between the visible and microwave portions of the electromagnetic spectrum. 30 micrometers = meters 3 micrometer = meter

19 Far infrared waves (longer waves) are thermal. we experience infrared radiation as heat. The Infrared

20 Shorter, near infrared waves are not hot at all - in fact you cannot even feel them. The Infrared These shorter wavelengths are the ones used by your TV's remote control.

21 The Infrared

22 Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light. Visible Light Waves

23 Ultraviolet Light Waves Though these waves are invisible to the human eye, some insects, like bumblebees and butterflies, can see them!

24 Our Sun emits light at all the different wavelengths in electromagnetic spectrum, but it is ultraviolet waves that are responsible for causing our sunburns. Black lights emit longer wavelengths of UV light Ultraviolet Light Waves

25 X Rays As the wavelengths of light decrease, they increase in energy. X-ray light tends to act more like a particle than a wave. X-ray detectors collect actual photons of X-ray light

26 X Rays X-rays were first observed and documented in 1895 by Wilhelm Conrad Roentgen.

27 Gamma Waves Gamma-rays have the smallest wavelengths and the most energy of any other wave in the electromagnetic spectrum. These waves are generated by radioactive atoms and in nuclear explosions

Sun in radio waves sun Sun 2 Sun 3 otherl pulsars sun Sun 2 Sun 3 otherl pulsars

Sun in microwaves

Sun in infrared

Sun in visible light

Sun in Ultraviolet (UV) light

Sun in x- rays

Sun in gamma rays

Happy Thursday! Get notes out from last time Pick up calculator Get out sheet of paper to take a few extra notes Due today: SHM worksheet Light and EM Notes/worksheet Raytheon tomorrow Doppler effect packet due Monday 3 rd quarter review

Speed of Light C = speed of light (3.0 x 10 8 m/s) λ = wavelength (m) f = frequency (Hz)

A reminder: λ and f The relationship between λ and fis an inversely proportional relationship. This means that as λ gets bigger f gets smaller, and as λ gets smaller f gets bigger.

Example problem If a wave has a wavelength of 5.4 x m, what is its frequency in Hz?

Example problem If a wave has a wavelength of 5.4 x m, what is its frequency in Hz? C = λ ∙ f

Example problem If a wave has a wavelength of 5.4 x m, what is its frequency in Hz? C = λ ∙ f 3.00 x 10 8 = 3.00 x 10 8 = 5.4 x f ∙

Example problem If a wave has a wavelength of 5.4 x m, what is its frequency in Hz? C = λ ∙ f 3.00 x 10 8 = 3.00 x 10 8 = 5.4 x f ∙ 5.4 x 10 -7

Example problem If a wave has a wavelength of 5.4 x m, what is its frequency in Hz? C = λ ∙ f 3.00 x 10 8 = 3.00 x 10 8 = 5.4 x f ∙ 5.4 x f = 5.5 x Hz

Diffraction of light This is how the waves of light look when Moving through a diffraction grating Diffraction divides light into different wavelengths

Calculate the frequency of microwave radiation if it has a wavelength of 12.3 cm. (Don’t forget to convert cm into m)

Color The spectrum is what Newton called the arrangement of visible light colors red light + blue light + green light = white light White light is a combination of the spectrum of colors, each having different wavelengths

Why does the light do this?

Why does the pencil look like this?

Answers: Because of “refraction”. Refraction is: “the change in a wave’s direction and speed that is caused by a change in the medium.” remember: 1. The “medium” is the material that the wave travels through. 2. The only thing that can affect the speed of a wave is if there is a change in the medium.

Characteristics of Refraction: All types of waves refract: Light waves, sound waves, water waves, etc. Longer wavelengths change direction less. Shorter wavelengths change direction more.

The speed of a water wave depends on the depth of the water. This means that water waves will refract (change speed and/or direction) near a shoreline. (This is why near the beach, the top of the wave “falls forward” – it is moving faster than the bottom of the wave!)

See how the waves aren’t parallel? Parts of each wave have changed direction due to refraction.

These waves changed direction a lot!

March 11, 2011 earthquake in Japan

 = 700 nm = 400 nm Q: How does a prism cause the colors to separate? A: The longer the wavelength, the less it is affected by refraction. The shorter the wavelength, the more it is affected by refraction.

Road Mirages are caused by refraction (the air directly above the road is hotter than the air that is a little higher up, so the light bends as it travels through the layers of air)

Slow down, Light! Light moving from less dense medium into a more dense medium slows down. – Example: when light goes from Air  Water – Think of a truck on a smooth road suddenly hitting a patch of sand at an angle * First tire to hit slows down * Truck turns because the tires have different amounts of traction. Air Water Incident ray ΘiΘi Refracted ray ΘrΘr

Speed up, Light! Light moving from more dense medium into less dense medium speeds up. – Examples: when light goes from Water  Air – Think of a truck on sand suddenly hitting a a smooth road at an angle – First tire to hit speeds up – Truck turns away from normal Water Air Incident ray ΘiΘi Refracted ray ΘrΘr

Index of Refraction Ratio of speed of light in a vacuum (3 x 10 8 m/s) to speed of light in a transparent substance is the index of refraction (n). The larger the n, the slower light travels n air = 1 (memorize this!) n = index of refraction (no units) c = speed of light (3 x 10 8 m/s) v = velocity of light in the transparent substance (m/s)

Sample Problem Ex: The hardest mineral is diamond, with an index of refraction of At what speed does light travel through a diamond? What percentage is this of the speed of light in a vacuum? n = 2.42 c = 3 x 10 8 m/s v = ? In a diamond, light only travels 41% of the “speed of light”

Index of Refraction for some common substances Vacuum 1 (by definition) Air Ethyl alcohol (ethanol) 1.36 Water 1.33 Diamond 2.42 Cubic zirconia (fake diamonds!) 2.15 to 2.18 Cornea (human) 1.37 to 1.40 Corn Oil 1.47 Crown Glass (pure) 1.50 to 1.54 Flint Glass (pure) 1.60 to 1.62 Pyrex (borosilicate glass) Salt 1.52 Sapphire 1.77

Critical Angle Critical Angle – the angle of incidence that produces a 90°angle of refraction Air n = 1 Water n = 1.33 ΘcΘc Θ r = 90°

Total internal reflection can be seen at the air-water boundary.

Total Internal Reflection Occurs when a light ray tries to escape for a dense medium into a less dense medium. If the light ray strikes the surface at an angle GREATER THAN the critical angle then it can’t escape – it is trapped inside the denser material. This is how fiber optics transfer info along glass fiber

Total internal reflection: The light waves can’t get out!

“Fiber Optic” cables use total internal reflection to transmit data long distances. (Cable TV & Internet)

Fiber Optic cables – the light finally escapes at the end of the line.

Using Refraction to Create Invisibility

Mirrors reflect, but lenses refract.

The exact shape of a lens, combined with the refraction, is how light can be focused:

This type of lens can be used as a magnifying class, or to start fires. The focal point gets very hot because all of the light converges to that point. (In Latin, the word “focus” means “fire place”.)

Refraction is how lenses are able to focus images: Light refracts in your eye at two different locations: 1 st at the cornea and 2 nd at the lens.

Inverse Square Law Light illumination follows the inverse-square law (like gravity)

Reflection of Light Law of Reflection for smooth surfaces, is called specular reflection Diffuse reflection for rough surfaces

Specular and Diffuse Reflection

The chemical process of coating a glass surface with metallic silver was discovered by Justus von Liebig in 1835, before that they coated the back of glass with tin and mercury, before that they had shiny silver plates, or very still water Mirrors became most popular with the French

3 types of mirrors Plane Concave Convex

Plain Mirror

Plain or Flat Mirror optical illusion of plane mirror animation

Refraction of light Bending of light as light moves from one media to another at an angle Draw diagram: Normal Angle of incidence Angle of refraction

Mediums Optically less dense – allows light to travel faster Optically more dense – slows down the speed of light,

Snell ’ s Law 1621, Dutch Scientist

Fish in the water problem:

Periscope:

Index of refraction Every substance has its own index of refraction It is the ratio of the speed of light in a vacuum to the speed of light in a given transparent medium

Demonstration! “ n ” is the index of refraction for that substance “ c ” is the speed of light in a vacuum “ v ” is the speed of light in that substance

Facts you need to know Light travels at different speeds in different substances Light bends as it changes media If c is slower in one medium than another, then the medium is optically dense When light passes from a more dense to a less dense medium, light will bend away from the normal When light passes from less dense to more dense medium, light will bend toward the normal.

For example: a light beam in air hits a sheet of crown glass at an angle of 30.0°. At what angle is it refracted? Homework: p. 400 #1-4

Total Internal Reflection  If the angle is smaller that the Critical Angle, the light will refract If the angle of incidence is at the Critical Angle, the light will move along the surface of the medium If the angle of incidence is greater than the Critical Angle, the light ray will reflect

Total internal reflection occurs only when light moves from from a medium of high index of refraction to a medium of low index of refraction For example: when light moves from water to air

Critical Angle When a light ray at a boundary does not refract, but moves parallel to the boundary

Practical Application Fiber Optics Total internal reflection only occurs when light moves along a path from a high index of refraction to a lower index of refraction

No Reflection and No Refraction

Refraction Causes: A sunset is a mirage Double moon is a mirage Optical illusions on hot days

Dispersion of Light White light being separated into the colors of the visible spectra Prism Dispersion of light in water droplets cause a rainbow

rainbow animation

Homework P.411 #31-58