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What Happened?? Look at the data you collected during the simulation Are the angles the same for every scenario? Why is there a difference?

Bending Is this similar to what you saw in the simulation?

Bending The change in speed that occurs at an interface or boundary between two different media

Bending of Light Why is there a change in speed? Running analogy…

Least Time Principle Light always takes the path that requires the least amount of time

Bending of Light The speed of a light wave is dependent upon the optical density of the material through which it movesoptical density

Bending of Light Optical density of a material relates to the tendency of the atoms of a material to maintain the absorbed energy of an electromagnetic wave

Energy transformation of the Light Energy is transmitted into the more dense medium and slows the wave

The bending of the path of light Refraction occurs as light passes across the boundary between two medium A synonym for refraction is "bending” Refraction

What is going on in this photograph? Refraction

SFA = Slow to Fast, Away From Normal If a ray of light passes across the boundary from a material in which it travels slowly into a material in which travels faster, then the light ray will bend away from the normal line

Refraction of Light When light rays enter a medium in which their speed increases (less dense) the rays bend away from the normal.

FST = Fast to Slow, Towards Normal If a ray of light passes across the boundary from a material in which it travels fast into a material in which travels slower, then the light ray will bend towards the normal

Refraction of Light When light rays enter a medium in which their speed decreases (more dense) the rays bend toward the normal

Refraction of Light This is caused by the change in speed of light as it passes from one medium to another How many times is the light refracted in the picture?

Refraction of Light This is caused by the change in speed of light as it passes from one medium to another

Refraction of Light Which medium is more dense?

Refraction of Light How does refraction causes the bottom of a clear lake or pool to appear? CLOSER !!!!

Recap Questions What is the cause of refraction in light waves? Describe the path a light ray will take when it travels from a less dense to a more dense medium. Use the NORMAL as your frame of reference. What is the main factor that determines the amount of refraction in light waves?

Refraction of Light The wave speed is always greatest in the least dense medium The wavelength is always greatest in the least dense medium

Refraction of Light The frequency of a wave is not altered by crossing a boundary However, both the wave speed and the wavelength are changed

Refraction The optical density of a material relates to the tendency of the atoms of a material to maintain the absorbed energy of an electromagnetic wave One indicator of the optical density of a material is the index of refraction value

Refraction INDEX OF REFRACTION (n) Defined as the ratio of the speed of light in vacuum to the speed of light in the medium index of refraction : n = c / v The speed of light in a given material is related to this quantity Every substance has its own specific index of refraction. The next slide has a few examples

MaterialIndex of Refraction Vacuum1.0000<-- lowest optical density Air Ice1.31 Water1.333 Ethyl Alcohol1.36 Plexiglas1.51 Crown Glass1.52 Light Flint Glass1.58 Dense Flint Glass1.66 Zircon1.923 Diamond2.417 Rutile2.907 Gallium phosphide3.50<-- highest optical density

Index of refraction values (represented by the symbol (n) It is the number of times slower that a light wave would be in that material A vacuum is given an (n) value of v = c / n n = c / v

Snell’s Law Snell's Law The relationship between the angles of incidence and refraction and the indices of refraction of two media n i sin θ i = n r sin θ r

Snell’s Law light crosses a boundary into a medium with a higher index of refraction, the light bends towards the normal Light traveling across a boundary from higher (n) to lower (n) will bend away from the normal

Snell’s Law Index of refraction ( n ) = c / v material Describes the extent to which the speed of light in a material medium differs from that in a vacuum n i sin  i = n r sin  r n i = index of refraction of incidence material  i = angle of incidence n r = index of refraction of refractive material  r = angle of refraction

Find the angle of refraction n i sin  i = n r sin  r  r = 32 o  r = 35 o

Lumination Luminous objects are objects which generate their own light

Illumination Illuminated objects are objects which are capable of reflecting light to our eyes None of us are light-generating objects It is only by reflection that we, see

Total Internal Reflection Total internal reflection, or TIR is the reflection of the total amount of incident light at the boundary between two medium Total internal reflection only occurs with large angles of incidence or if you exceed the critical angle

Total Internal Reflection TIR only takes place when f the following conditions are met 1. the light is in the more dense medium and approaching the less dense medium. 2. the angle of incidence is greater than the critical angle **If the ray is at 90 0 there is no refraction**

Total Internal Reflection Critical angle - the minimum angle of incidence for which a light ray is totally reflected within a medium. Total internal reflection - the100% reflection of light that strikes the boundary between two media at an angle greater than the critical angle.

Total Internal Reflection Optical fibers - a transparent fiber that can transmit light down its length by means of total internal reflection. The light travels through the core by constantly bouncing off the cladding. The cladding does not absorb any of the light.

The maximum possible angle of refraction is 90-degrees if the angle of refraction were greater than 90 degrees, then the refracted ray would lie on the incident side of the medium - that's just not possible

The maximum possible angle of refraction is 90-degrees if the angle of refraction were greater than 90 degrees, then the refracted ray would lie on the incident side of the medium - that's just not possible

Critical Angle  critical = sin -1 ( n r / n i ) the critical angle is defined as the angle of incidence which provides an angle of refraction of 90-degrees For the water-air boundary, the critical angle is degrees

Critical Angle

The following slides can be optional

The Rainbow The conditions for a rainbow are 1. that the sun must be shining on one part of the sky and 2. water droplets in a cloud or a falling rain must be in the opposite part of the sky

The Rainbow The water droplets refract the light twice and reflect the light as well AT this first refraction the light is dispersed into its spectral colors (red bent the least, violet the most)

The Rainbow The second refraction acts like a prism, where refraction at the second surface increases the dispersion already produced at the first surface

The Rainbow Everyone sees their own personal rainbow It is based on your location

Atmospheric Refraction Mirage: a floating image that appears in the distance and is due to the refraction of light in the Earth’s atmosphere  The image appears upside down, to an observer just as if it were being reflected from a surface of water ** the light is not reflected; it is refracted  Undeflected wave fronts would travel at one speed; the greater speed near the ground, however the causes the light ray to bend upwards

Atmospheric Refraction After the sun has set one would think it was still setting, this is because light is refracted by the earth’s atmosphere  The density of the atmosphere changes gradually, the refracted rays bend to produce a curved path  When the sun is near the horizon, the rays from the lower edge are bent more than the rays from the upper edge; this makes the sun appear elliptical instead of round

Dispersion in a Prism Since different frequencies of light travel at different speeds in transparent materials, they will refract differently and bend at different angles Dispersion - the separation of light into colors arranged according to their frequency

The end

Reflection Reflection: when a wave reaches a boundary, some or all of it bounces back into the first medium Totally Reflected waves are reflected back rather than transmitted into another object Partially Reflected some energy is transmitted into a new medium

Reflection Luminous objects emit light in a variety of directions your eye only sees the very small portion of rays coming towards it Ray = a narrow beam of light

The Law of Reflection Normal = imaginary line drawn perpendicular to the surface

The Law of Reflection angle of incidence = The angle made by the incident ray and the normal angle of reflection = The angle made by the reflected ray and the normal

The Law of Reflection angle of incidence = angle of reflection

The Law of Reflection

Summary Questions. 1. Differentiate between the angle of incidence and the angle of reflection 2. What is meant by the normal to the surface? 3. What is the law of reflection

Pop Quiz 1. Consider the diagram at the right. Which one of the angles ( A, B, C, or D ) is the angle of incidence? Which one of the angles is the angle of reflection? 2. A ray of light is incident towards a plane mirror at an angle of 30-degrees with the mirror surface. What will be the angle of reflection? Answer: 60 degrees. Note the angle of incidence is not 30 degrees! Answer: B

Mirrors light reflects off surfaces in a very predictable manner - law of reflectionlaw of reflection Rays of light are reflected from mirrors in all directions The Law of Reflection is Always Observed (regardless of the orientation of the surface)

Mirrors Virtual images are images which are formed in locations where light does not actually reach

Mirrors Virtual Image are formed through reflection that can be seen by an observer but can not be projected on a screen light from the object does not actually come to a focus

Mirrors Your eyes cannot differentiate between a real image and a virtual one Your image in a plane mirror is? ALWAYS VIRTUAL !!!

Specular Specular reflection Reflection off of smooth surfaces such as mirrors or a calm body of water

Diffuse Diffuse reflection When light is incident on a rough surface and is reflected in many directions. What constitutes a rough surface for some rays may be a polished surface for others.

Diffuse vs. Specular What is the main type of reflection occurring here?

Diffuse vs. Specular What type of reflection is occurring in picture A? B? A B