What we did today! 

Tues. Ap.  6

Rayleigh Scattering:  Short wavelengths scatter more than long wavelengths.
    What makes the sky blue during the day?
    Why is the sky red at sunrise and sunset?
    What is the color of clouds and how is it produced?

Law of Refraction:  Snell's Law.
The index of refraction of two materials and the angle at which a light ray will  propagate through those two media are related through Snell's Law.  A ray with incident angle, Q, traveling through a material with index, n₁, will refract at an angle, f, in a material of index, n₂.
 

                                         n₁ sin Q =  n₂  sin f

Lenses: There are two main type of lenses -- converging and diverging -- also known as convex and
concave respectively.  When light rays travel through these lenses they are bent (refracted) because of the
difference in index of refraction of the air and the glass of the lenses.  Upon exiting the lenses, the light rays are
bent away from the normal line and because of the curvature of the lenses this produces different efffects.  For a
converging lens (with convex surfaces), parallel input rays are bent so that they converge to a single point (thus
the name).  For a diverging lens (with concave surfaces), parallel input rays are bent so that they spread out
away from the lens as the exit (again the beam will diverge).

See this link for more information:  link to miniexperiments and other lens info

Eyeballs and Glasses:
    Myopic eyes are near sighted. This means that the lens creates an image too close to the eye's lens for objects that are far away (so that the image is in front of the retina).  The eyeball is slightly distended.  Correction for such an eyeball requires a diverging lens.
    Hyperopic eyes are far sighted.  This means that the lens creates an image too far from the eye's lens for nearby objects (so that the image is behind the retina).  The eyeball is slightly squashed.  Correction for such a difficulty requires a converging lens.
    Contact lenses use differing indices of refraction as well as curvature to correct for vision problems, while glasses only use curvature.

Total Internal Reflection -- Fiber Optics:
    Light coming from a high index material like glass into a low index material like air undergoes refraction (bending away from the normal line) until it reaches a critical angle.  Then it can no longer exit the glass and is totally reflected within the material (total internal reflection).  This is how light propagates (travels) down fibers.  It is sent into the fiber at angles greater than the critical angle and thus reflects and bounces its way down the fiber.  The fiber can be bent as long as it does not become so tightly bent that the angle for total internal reflection is lost.  Then the light would escape.

Ch. 18 HW
Qs 1,2,21,22,31,32,33,36,49,57
Es 1,3, Example 1 & 2 using Snell's law and lens law

Tues. Mar. 30 and Thurs. Ap. 1

Light, Color & Optical Communications -- Ch. 15 & 17

How is light made?
Excitation of electrons to high energy levels is followed by electrons dropping
to their ground (or un-excited states)  This means they give up energy to make the transition and that energy is
given off in the form of photons.  Photons are packets of light energy that have just the right amount of energy to
shift the electron from one energy level to the other.

Light's Wave Nature:
Light propagates from one place to another as a wave.  It has wave properties of diffraction,
interference, reflection, and refraction.

Wave Properties:

Wavelength, lambda
Frequency, f
Period, T                      T = 1/f

Wavelength * Frequency = Speed of Wave

Speed of light, c

Interference of Waves:  Two waves superimpose on each other.  The amplitudes at a given location are added to find the resulting waveform.  Amplitudes above the equilibrium point are positive and those below the equilibrium point are negative.

Constructive Interference:  Occurs when both waves are in phase with each other.
Destructive Interference:  Occurs when each wave is out of phase with the other, by 180 degrees.

CH. 15 HW
Qs 19,20,22,23,31,32,34,35,37
Es1,4,13,15,17,19

Light's Particle Nature:
Planck was the physicist who derived the theoretical expression which describes the intensity of light
given off as a function of wavelength for a given temperature black body radiator.  It was based on the
idea that each electron could only give off energy in discrete amounts rather than any and all energies.

                    E = h f           c = l f = 3 x 10⁸ m /s

In order to describe spectra, scientists had to model the atom with different energy levels so that light
could be absorbed or emitted in discrete amounts also.  The photons which interact with the atoms have
to have just the right amount of energy to get the electron to jump from one orbital to another (or one
energy level to another) or the photons are not absorbed or emitted.  This idea came from Einstein
when he studied the photoelectric effect.

How does light act?  Light travels from one place to another as a wave; it interferes with itself, it diffracts going
through an aperture (small hole).  It interacts with matter via absorption and emission as a particle.  It reflects off
of surfaces of materials, refracts (or bends) when it enters a material with a different index of refraction (related to
density),  and can be absorbed by the material. This is known as wave- particle duality of light.

Law of Reflection:
The angle of incidence of the light ray is equal to the angle of reflection of the
ray off a material.
 

                                                                 Qincident  = Qreflected

Mirrors utilize the law of reflection and lenses utilize the law of refraction.

Flat Mirrors:  Provide an image of a person which is upright, on the other side of the mirror, but reversed right to left.

Concave Mirrors: Will focus light.  They also make an image which is inverted if you stand beyond the focal point of the mirror but is upright and huge if you stand within the focal point.

Convex Mirrors:  Will diverge light (spread it out).  They also make images on the opposite side of the mirror which are smaller and upright.

HW Ch. 17
Qs 1,2,15,16,17,21,37,38,43
Es 21,22,24

Thurs. Mar 11, Tues. Mar 23, & Thurs. Mar. 25
Website Presentations

Website Presentations and Discussions:

Tues. Mar. 9

NEW TOPICS!! -- Light, Color & Optical Communications --Ch. 23, 15 and 17-19 + WebInfo

What's coming this semester -- Nanotechnology, optical communications -- all based on knowledge of the ATOM

• Atoms:  What are they?  What do they look like?  & What are their characteristics?

• Light:  What is it?  How is it produced? & What are its characteristics?

Tues. Feb. 24 & Thurs 26

Ch. 7 -- Energy

Main Ideas:

Work:    Can be defined in a number of ways.  It is related to changing the state of
motion of an object, changing an objects position, and/or changing its state of energy.

                                   W =  F d  = DKE  = DPE

F is force, d is distance, KE is kinetic energy, and PE is potential energy.  Applying a force over a distance can increase the
speed of an object or change its potential energy.

                                    KE = 1/2 m v2

Is energy due to motion of an object.  Any object in motion will exhibit KE.  It is a
scalar quantity NOT a vector quantity.

                                     PE = m g h

Is energy due to position above or below a reference height.  PE can be negative if
work must be done on the object to move it to your reference height.

                              Power = Work/Time

This describes how quickly you do the work.  The quicker it is done the more power is required.

Conservation of Energy states that energy can neither be created nor destroyed, it
simply changes states (or types of energy).

Conservation of Mechanical Energy states that a system that is isolated can exhibit
conservation of mechanical energy. That is the total energy of the system comes from the sum of PE and KE and as the system

evolves:

                               KE + PE = Constant.

In-Class Demonstrations and Calculations of W and
Conservation of Mechanical Energy.
 

Examples of Conservation of Energy:

 (1)  A 1 kg pendulum swings from a starting position of 50 cm above equilibrium. What is its speed at the bottom of its
swing?

(2)  The same pendulum swings to 15 cm above equilibrium.  What is its speed there?

CH. 7 Homework
Qs 2,5,8,12,26,27,30,35,36,39,40,49,51,52
Es 1,3,6,9,13,17,19,22,23

Thurs. Feb. 12 & Thurs. Feb. 19th

Main Ideas:

Linear Momentum                                   p = mv

Newton's Second Law                              F = (p_f - p_i) / t

Impulse                                                 F Dt = D(mv)

        In order to change an object's momentum, you must apply a force for a period of
time.  If you increase the time, you can decrease the necessary force.

Conservation of Linear Momentum           p(before) = p(after)

Fermi Lab:  <http://www.fnal.gov:80/> Go see how conservation of momentum and
energy are used in real life!

Angular Momentum                                L = mvr

Conservation of Angular Momentum   L(before) = L(after)
 

        Momentum is a vector quantity defined as   p = mv where p and v are
        vectors.

        Momentum is a conserved quantity when there are no external forces
        acting on a system.

        Elastic Collisions are ones in which both momentum and kinetic energy
        are conserved.

MINI EXPERIMENT

Main Ideas:
Example problems on conservation of momentum -- group work

Experiment:  Momentum Conservation
             2 Carts on Track, Stop watches

Estimate the relative masses of the two cars (individually and with masses on
one).

Draw a picture of the situation.

Estimate the speed of one car through experimentation.

Calculate the speed of 2nd car (or both for inelastic) using conservation of
momentum.

3 cases:

a)  Elastic collision with both cars same mass.
b) Elastic collision with one car has 1 metal bar on it.
c)  Inelastic collision with 2nd car intially at rest with metal bar on it.
 

CH. 6 Homework
Qs 4,7,15,18.20,27,28,33,34,37,39
Es 1,3,5,7,13,14,17,18,20

Tues.  Feb. 3

F = ma                  F = D(mv)/Dt

In  Class Work:
              Define Newton's 3 Laws

              Give examples of each as you would explain them to a friend.

Focus in on Newton's Laws:

1.  First and Second Law:  The NET force is the important quantity.  If there is a NET
force, there is an acceleration.  If there is NO NET force, there is no acceleration; BUT there can still be motion (constant speed in  straight line).

2.  Examples of Places where net force must be considered:

Falling objects and air resistance.
Pushing objects across a surface and friction force.

3.  Third Law:  Action and Reaction Pairs, Which forces need to be largest to get an
object to accelerate in a  particular direction.

Examples of Newton's Laws -- Net force and terminal velocity

Units of Force, Weight, Mass

CH. 3 Homework
Qs 3,5,7,17,19,25,26,29,31,37,40,
44,47,50,52
Es 1a&b,3,6,7,10,14,17,19,24

Tues. Jan. 27 & Thurs. 29

 Terminal Velocity & Graphing

What does each type of graph look like for the following
situations:

        Constant Motion -- the distance increases with time (straight line with some slope, the steepness of the line is related to the speed), the speed stays the same regardless of time (straight horizontal line), the acceleration is zero

        Acceleration -- The distance increases or decreases with time but the slope changes (as you speed up the slope increases, as you slow down the slope of the curve decreases) thus you see a curved line on distance graph, the speed incresases of decreases with time in a linear fashion (straight line with some slope corresponding to acceleration), the acceleration is a constant at all times (straight horizontal line (non-zero, may be positive or negative))

        No Motion -- the distance remains the same regardles of time (straight horizontal liine), all other graphs are at zero (no speed and acceleration)

        Changing Acceleration -- all graphs are more complicated, distance changes with time in a curved fashion and so does speed, accelearation is changing with time (straight line at some angle)
 

Graphing of Scenerios
Ex. Dog runs ambles down street at constant pace, sees a cat and speeds up
to chase it at a full run, cat ducks into doorway and dog must decelerate to
a stop.

Ex.  Hawk sitting in tree, sees a mouse, dives going faster and faster to a high speed,
swoops across the field, grabs for mouse but misses, flies dejectedly at a lower speed
to a fence post, lands on post feeling sorry for itself.

Identify types of motion in scenerio, make 3 qualitative graphs of the
motion (d vs t, v vs t, and a vs t)
 

Graphing Homework:
Handouts available on web
Read Ch. 3

Tues.  Jan 20 , 2004
Intro. to Ch. 2 - Motion 

Equipment:  Meter sticks & stop watches

Using the above tools and the people in your group.  Measure the
following quantities.

a)  Average speed of a person walking at constant pace.

b)  Average acceleration of person starting from stop to a run.

c)  Your response time when dropping a ruler between fingers
 

Experimental Procedure:   Describe below how you would do the
above 3 measurements.

How many trials would you do? Why?

Data:   Record data below and show calculations of speed,
acceleration, and response time.

Analysis:  Are the values you calculated reasonable?  why or why
not?

What are possible sources of error?

Looking back would you change your experiment in any way?
How?

Key Concepts:

Speed -- average and instantaneous

Velocity

Vector Quantities

Acceleration - average and due to gravity

Free fall and Air resistance -- Terminal velocity

Homework Ch. 1
Es 11, 12

Homework Ch. 2

Qs 1,2,4,6,9,15,25,26,40,43,46  
Es 3,5,7,12,14,21,23 
 
 

Tues. & Thurs.  Jan. 13,& 15 2004
Introduction To Phy 101 

 1.  What is physics?

2.  What is technology?

3.  What new scientific discoveries have happened in your lifetime?

4.   What new technological developments have occured?

5.  How have the above two effected our lives?

6.  In what way have we (as members of society) shaped technology
and
science?

Assignment:   Read CH. 1