A Visual Review Lyzinski Physics Light Where does

A “Visual” Review Lyzinski Physics

Light? Where does it come from? It comes from moving electrons - different energy levels in an atom - when light jumps UP, it absorbs energy (usually in the form of heat) - when light jumps DOWN, it emits energy in the form of light. - the color of the light depends on the size of the jump. Moving electrons set up a changing electric field that also induces a changing magnetic field. Electromagnetic Waves!!!!

Light? What is it (what is it like)? • It is both wave-like AND particle-like. • It is a transverse, electromagnetic wave - Transverse (light) vs. longitudinal (sound) - Electromagnetic wave The approximate speed of light in a vacuum (or in air) - No medium needed • It travels at the speed of light (c = 3 E 8 m/s) • It travels in straight lines rectilinear propagation • It travels in rays (infinitely thin)

The Wave Equation General Equation: works for sound, water, slinkies, light, etc. Velocity Frequency Wavelength For light, Light Equation • Increase l, decrease f. • Decrease l, increase f.

The Electromagnetic Spectrum Radio AM FM Micro Infra ROYGBIV Ultraviolet X Gamma

AM vs. FM 535 -1605 k. Hz 88 -108 MHz Lower frequency Higher frequency Longer wavelength Shorter wavelength k. Hz = kilohertz = 103 Hz MHz = megahertz = 106 Hz

Some Helpful Applets showing longitudinal AND transverse waves. http: //www. kettering. edu/~drussell/Demos/wavemotion. html Applet explaining how a moving electron (jumping and falling in energy level) produces a wave. http: //www. colorado. edu/physics/2000/waves_particles/wavpart 4. html Applets showing a 3 D electromagnetic wave. http: //www. walter-fendt. de/ph 14 e/emwave. htm http: //www. amanogawa. com/archive/Plane. Wave-2. html

Plane Reflectors Incident Ray Normal Reflected Ray Rule #1: The angle of Incidence equals the angle of reflection. Rule #2: The normal, incident ray, and reflected ray all lie in the same plane.

Drawing PLANE MIRROR Ray Diagrams 1. Draw two incident rays from a point. 2. Find the intersection of the two reflected rays. C C’ 3. Repeat for every point on the object B’ B mirror

Spherical Mirrors Light “Caves in” on the Focus CONCAVE (CONVERGING) Notice that qi = qr C F Principal Axis Center of Curvature Focus f = focal length R = radius of curvature

Spherical Mirrors vs. Parabolic Mirrors Large spherical mirrors have an avoidable issue. Near the edges, reflected rays might not reflect through the focus. w R This is known as SPHERICAL ABBERATION . It can be corrected by…. . using mirrors whose width (w) is smaller than its radius of curvature (R). OR …. . using mirrors that are PARABOLIC, instead of spherical

Spherical Mirrors CONVEX (DIVERGING) C F Principal Axis Center of Curvature “Virtual” Focus Again, Notice that qi = qr f R

Image Formation Cone of rays seen by the human eye What does your eye see? ? ? Object Image Virtual (cannot be formed on a screen) Plane Mirror

Characteristics of Images Real VS Virtual Can be formed on a screen ATTITUDE Can NOT be formed on a screen Upright VS Inverted TYPE or “Orientation” Larger Smaller Same size

Image Formation (continued) In Spherical, CONCAVE mirrors, a clear image is formed where all the reflected rays emitted from any single point on the object intersect. A screen placed here will have a focused image on it. A screen placed here will have a “fuzzy”, unfocused image on it.

How do you locate the image in a Spherical Mirror Situation. Pick a point on the object (usually the one furthest from the principal axis), and then draw 2 intersecting rays that obey the following rules: 1. Any ray parallel to the principal axis is reflected through the focus. 2. Any ray through the focus is reflected parallel to the principal axis. 3. Any ray through the center of curvature is reflected back along the incident ray (back along itself)

Concave Mirrors “OUTSIDE“ the focus C F Moving towards the focus, the image is REAL, inverted, and gets larger.

Concave Mirrors “ON” the focus C F When an object is at the focus, it doesn’t have an image.

Concave Mirrors C F “INSIDE” the focus Moving towards the mirror, the image is VIRTUAL, UPRIGHT, and gets smaller (although the image is still larger than the object itself).

Convex Mirrors Note: All images are in front of the virtual focus. F C When an object gets closer to the mirror, its image is VIRTUAL, UPRIGHT, and keeps getting smaller (and the images are always smaller than the object).

Wanna play with mirrors? try an applet at …. . http: //webphysics. davidson. edu/physlet_resources/optics 4/default. html

Mathematically locating an image All distances are measured from the mirror’s vertex Mirror Equation Distances are POSITIVE for REAL images/objects Distances are NEGATIVE for VIRTUAL images/objects Heights are positive when measured upward and negative when measured downward. M is the magnification. Magnification Equation

A few Helpful tips to using the equations. Always write out a list of do, di, ho, hi, f, and M first. Using knowledge of the type of mirror you have and where the object is placed, make sure the SIGNS are correct on your variables before plugging the variables into the equations. ALWAYS check your answers to makes sure that they 1) match your drawing 2) have signs that make sense 3) have numbers that make sense.

Example A converging mirror is used to take a 4 meter tall object and create a 2 meter tall image of it that is formed on a screen. If the object is 3 meters from the mirror, find the mirror’s focal length, the image distance, and the magnification. hi = -2 m (negative because it must be upside down, since real images in a converging mirror are always inverted). ho = 4 m do = 3 m f = + ___ (since it’s a concave, converging mirror) di = +___ (since it’s real) -1 < M < 0 (since its inverted and smaller)

Another Example A mirror is used to create a small, upright image. If the radius of curvature of the mirror is 40 cm, and if the image is 4 times smaller than the object, how far in front of the mirror has the object been placed? THE mirror must be diverging since only convex mirrors can create smaller, upright images! Therefore, f = -20 cm. Also, M = +1/2 (since the image is half the size of the object). You have to use a substitution method on this problem, yielding: di = - ___ (since the image is virtual) do = + ___ (since the object is real)

Concave mirrors Can make small objects appear larger Make-up mirrors, shaving mirrors Convex mirrors Can make large objects appear smaller (see a WIDE view) Security mirrors, Driveway mirrors, Car door mirrors

Uses for PARABOLIC mirrors (in case you were wondering ) At solar power plants, parabolic “troughs” (as they’re called) are used to focus light onto a fluid carrying pipe, thus heating the fluid and producing useable energy. Fluid filled pipe being heated http: //www. solarserver. de/lexikon/parabolrinnenkraftwerk-e. html Parabolic trough