# Reflection and Refraction of Light. Reflection of Light Every object absorbs some light and reflects some light Why is the sun different? – The sun makes.

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Reflection and Refraction of Light

Reflection of Light Every object absorbs some light and reflects some light Why is the sun different? – The sun makes its own light – The light that comes from your table to your eyes is from the sun or a lamp and then reflects to your eyes How can we trace light? – Ray diagrams are used to trace the path of light

Ray Diagrams

How does light reflect? Light reflects at an angle Rough surfaces - light that strikes the surface will be reflected at all angles – Called DIFFUSE REFLECTION Smooth surfaces – light that strikes a smooth surface like a mirror will all reflect in a single direction

How do you see something? Light from the sun appears white, however when shone through a prism, it will separate into various colors (visible spectrum of electromag. waves) Objects have color because they reflect certain wavelengths of light

Why does a plant appear to be green? It absorbs the other wavelengths and reflects the green light (550 nm) Light really is not “green” – your brain interprets light at certain wavelengths as certain colors Petals of a red rose look red because they absorb wavelengths and then reflect the red light

What is being absorbed? Light energy is energy! A transparent object allows the energy to pass through, opaque objects absorb some of that energy (usually turning it to heat energy)

Black is not a color – it is the absence of color

Refraction of Light What happens to light waves when they travel? Through empty space – travel in straight line Refraction – how light bends when passing from one medium to another Light changes direction because the speed of light is different in different mediums

How is light refracted? When light goes from traveling fast to a medium where it is traveling more slowly, the ray will be bent toward the normal Like one wheel of a lawnmower hitting the grass Like a car wheel going into the sand When light goes from traveling slower to a medium when it is traveling faster, the ray is bent away from the normal

How do objects appear if light is refracted? Objects appear to be in a different position The path of the light is changed as it goes from one medium to another However the brain still sees it as though the light traveled in a straight line So, the position of the object (cat or fish) looks different than where it really is

Diffraction Diffraction is the BENDING of waves around an edge. – Ex- Hearing sound waves from around a corner – When waves pass the edge of an object or pass through an OPENING, they spread out as if a new wave were created there. – Diffraction is the reason a SHADOW never has perfectly sharp edges.

Wave Interference

When several waves are in the same location, the waves combine to produce a single new wave that is different from the original wave.

1) Constructive Interference: when two waves interact and the resultant wave has a larger amplitude (Part A, Figure below)

2) Destructive Interference: when two waves interact and the resultant wave has a smaller amplitude (Part B, Figure below)

INTERFERENCE IN LIGHT WAVES: (transverse electromagnetic) Create colorful displays Ex- soap bubbles- pg 476 – You see many colors because the light is bouncing off different parts of the bubble (creating differing wavelengths) – These waves interfere constructively in some places and destructively in others. – These different frequencies are interpreted by your eyes to create many different colors.

INTERFERENCE IN LIGHT WAVES: (transverse)

INTERFERENCE IN SOUND WAVES: (longitudinal mechanical) If two waves are “out of sync” they cause “beats” of louder noise (when they are in line and have constructive interference) and then quiet (when they are opposite and destructive interference occurs) http://library.thinkquest.org/19537/Physics5.h tml http://library.thinkquest.org/19537/Physics5.h tml

STANDING WAVES: Form when a wave is reflected at the boundary of a medium. – Interference of the original wave with the reflected wave causes the medium to vibrate in a stationary pattern that resembles a series of loops. – The wave appears to be standing still, but it is not!!! (actually moving in both directions)

NODES- – Lie at points where the crests of the original waves meet the trough of the reflected waves, causing complete destructive interference. ANTINODES- – Midway between the nodes lie points of maximum vibration – This is where the crests of both waves meet creating complete constructive interference.

http://paws.kettering.edu/~drussell/Demos/s uperposition/superposition.html http://paws.kettering.edu/~drussell/Demos/s uperposition/superposition.html

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