3What is Light?Early theories of light varied. One was that your eyes emitted beams that would illuminate things for you. That was why you could only see when your eyes were pointed at something(~500 BC).Eventually people came to believe that light was either a wave or a bunch of moving particles.Einstein coined the term “photon” which represents the tiny massless particle that light may exist as.
4What is an electromagnetic wave? Remember waves transfer ______ not matter.The waves we have studied so far have all traveled through matter.An electromagnetic wave does not need matter to travel through.It can travel in a vacuum.An electromagnetic wave is a wave of oscillating electric and magnetic fields that moves at the speed of light.
5What is light?Since, em waves have both magnetic and electrical qualities;the two qualities exchange energy back and forth through induction.This causes the em waves to propagate and spread.
6Speed of light in a vacuum is constant in universe: 300,000,000 m/s Measuring the speed of lightJust how fast is light?Speed of light in a vacuum is constant in universe: 300,000,000 m/s7.5 round trips around the earth in one second8 minutes from the sun to the earth4 years from the nearest star, Alpha Centauri100,000 years to cross our galaxysome galaxies are 10 billion light years away
7Measuring the speed of light A “light year” is a measurement of distance based on how far light can travel in a single Earth year. How far is a light year?Distance = velocity x timeLight year = 300,000,000 m/s x 1 year= 300,000,000 m/s x 1 yr x 365 day/yr x 24 hr/day x 3600 s/hrLight year = 9.5 x 1015 mOr9,500,000,000,000,000 m
8So, the speed of light is: What is the frequency of a beam of light that has a wavelength of 1014 m and it is traveling in a vacuum?
97 types of Electromagnetic waves (7 types of light)radio waves, microwaves, infrared,Visible light, ultraviolet, x-rays, & gamma rayslowest frequency WE CAN SEE is redhighest frequency WE CAN SEE is violet (more energetic)
10Red Orange Yellow Green Blue Indigo Violet ROY-G-BIVRed Orange Yellow Green Blue Indigo Violet
11When light energy hits an object, the energy in the light causes the electrons in the material to vibrate.When this happens, a number of different things can occur.One of these things is:
12The object can be: Transparent to Light Transparent: lets light pass through in a straight lineGlass and water are transparent to visible lightSpring and ball model of light transmissionlight causes springs and balls to vibratevibration transfers within the materialenergy is released on the other side
13Transparent to Light Glass Example: Glass, like what makes up our windows, is transparent to visible light (what lets us see)In other words, glass transmits visible light through it. This is a good thing! Mr. Stief wouldn’t be able to see if his glasses didn’t do this!BUT! Glass doesn’t transmit UV rays (in other words you are safe from sunburn due to UV radiation if you sit by a closed window). Glass likes to hold onto UV radiation. But what happens to that energy then?Results in heat
14Opaque MaterialsAn opaque material absorbs certain frequencies of visible light but reflects other frequencies (it does not transmit light).We perceive the color of something based on the colors that get reflected off an opaque material.
15What is the speed of light? Can we ever say that the speed of light is less than this number? How?What is the difference between a transparent material and an opaque material?
16Shadows A shadow is formed when a light ray cannot reach a surface total shadow: umbrapartial shadow: penumbralight from another source fills inlarge source only partially blocked
17Polarization Light is a transverse wave Light from most sources vibrates in all planesEach light ray can be considered to have horizontal and vertical componentsSeparating vertical and horizontal components is called polarization
18PolarizationPolarizing filters are like sewer gratings that look like slits.Light waves vibrating in the plane of the slit can make it throughLight waves that vibrate perpendicular (at a 90 degree angle) to the grates cannot make it through
19PolarizationA single polarizing filter will let about one half of the light throughTwo polarizing filters aligned in the same direction will still let about one half of the light throughTwo polarizing filters aligned perpendicular to one another will let almost no light through
20Applications of Polarizing Filters Sun Glassesreduce glareblock out half of the light3-D movies
21Why is the sky blue?Where do rainbows come from?
22Diffraction When waves bend around an object The smaller the object compared to the wavelength, the more the bending.Wavelength and velocity stay the same.
23So, the sky is blue due to the fact that as white light (a combination of all the colors in the visible spectrum) hits our atmosphere, the light diffracts and spreads across the sky.However, it just so happens that due to the size of the gas particles in the sky, blue and violet diffract (bend around a barrier and spread out) the most, so we see the sky as blue.The sky is blue because:light diffracts in out atmosphereBlue and violet diffract the most so we see blue
24Diffraction of Light What type of wave gets diffracted more? Blue and violet bend the leastRed bends moreLower frequencies/bigger wavelengths diffract the mostHigher frequencies/smaller wavelengths diffract the least
25· Why is it hard to pick a penny off of the bottom of a swimming pool?
26Why is it difficult to catch a fish with a spear Why is it difficult to catch a fish with a spear? (think of why it your hand looks all squishified when you look at it in a sink full of water?)
27Refraction:when a wave passes from one medium to anotherThis occurs in a change in wave speedIf the incident wave is not straight on, the wave direction will changeSome waves wavelength also change
28Since the wave bends as it goes from one medium to another, the fish looks like it is in a different place
29What does it mean for a wave to get diffracted? Example? What does it mean for a wave to get refracted? Example?So where do rainbows come from?
30Light can be bent as it passes in different media Light can be bent as it passes in different media. This is how a mirage occurs. It is the bending of light as it passes through different temperatures of air.And it is why some roads look wet on a hot day
31So, when a wave hits an object, a number of things can happen So, when a wave hits an object, a number of things can happen. They are:Transmit (go through)RefractGet absorbedIn some cases, get diffractedAnd they can get REFLECTED!
32Reflection - how a mirror works Smooth surfaceDefinitionsIncident ray is the ray moving toward the surfaceReflected ray is the ray moving from the surfaceNormal is an imaginary line perpendicular to the surface
33More DefinitionsAngle of incidence is the angle between the incident ray and the normalAngle of reflection is the angle between the reflected ray and the normal
35Bill looks at Emily’s reflection in the mirror Bill looks at Emily’s reflection in the mirror. Draw the position of Emily’s image. Draw the path of the light rays that travel from Emily to Bill.BillEmily
36Concave Mirrors: (like a cave!) Satellite dishes are like concave mirrors shaped like a parabolaImage from a concave mirror depends on the placement of the object in relation to the mirror
37Convex MirrorsA convex mirror is shaped like the outside bottom of a spoon.Convex mirrors are used as rearview mirrors in cars and in stores to observe shoppers.Both of these types of mirrors still obey the law of reflection