Hypothesizing for the next lab

E block - please try to have this prepared for Tuesday (December 2).  Don't worry if you are still confused.  I just want us to have somewhere to start our conversation.


Upon our return to class after Thanksgiving, we will begin a new formal lab.  This lab is all about convex and concave lenses and mirrors.  You have played with lenses and mirrors a bit in class.  For our next class, please write a formal hypothesis for this experiment.  The hypothesis should address the following:

How will the distance between object and lens affect whether or not an image is formed, how (relatively) large the image is (bigger/smaller) and whether or not the image is right-side up or upside-down?  Also, address what types of optics (concave or convex lenses and mirrors) will produce images (real or virtual).

FYI - a "real" image can be projected onto a screen (think of setting fire with a magnifying glass), whereas "virtual" images are only seen "inside" lenses or mirrors (think of looking at yourself in a bathroom mirror).

Answers may be something like:

- I believe that all images will form at the focal point, and I think that all images will be real.
- I believe that images will only form if the object is very close, but that these images will be virtual.
- I believe that images will be formed only when the object is between the theoretical focal point and twice the theoretical focal point, and that these real images will always be smaller than the object.
- etc.

Be sure to type out your hypothesis and keep a copy for your formal lab report - I will be checking these at the beginning of class.

What to expect on the quiz

1.  Doppler effect
- use of the formula (be sure to understand 't a t a')
- understanding what it means
- red shift, blue shift

2.  Use of trig - Be sure that you can solve for things like:
- sin 20
- finding angle when you know the sine - for example, what is theta when sin(theta) = 0.75

3.  Snell's law and refraction

n = c/v

v = frequency x wavelength

n1 sin (theta 1) = n2 sin (theta 2)

There are two other versions of Snell's law, but you don't actually have to use them - in fact, if you are confused by all the formulas, just forget that those exist and use only the 3 above.

4.  Being able to draw the refracted path when light goes from one medium to another.

SAMPLE PROBLEM:

Light (wavelength 585 nm) goes from air to a new material.  Angle of incidence is 40 degrees and the angle inside the material is 20 degrees.  Both angles are measured with respect to the normal/perpendicular line.  Find the following:

a.  index of refraction of material
b.  speed of light inside material
c.  frequency of light
d.  wavelength of light inside material

Summary

HW (for F Weds, A Thursday)

Note:  We will have a quiz on Friday (F) and Monday (A).

Review the variations of the Snell's law equations and create/solve a problem which asks for:

- refracted ray angle
- refracted ray wavelength, speed, and frequency

Consider an equilateral triangular prism of glass (n = 1.5).  A light ray hits it on the left side such that the ray refracted inside the glass runs parallel to the bottom of the prism.  Find the initial angle of incidence (theta 1) on the left side.  Find also the exiting angle on the right side of the prism.

A (also):  Finish informal lab calculations.  Look up the index of refraction of salt water.  Are you close?  Does it change a lot from regular water?

HW for Tuesday A block and Wednesday F

HW due Friday for A, and Monday for F

Look up these terms and write down definitions and/or equations:

index of refraction

Snell's law

A picture may be useful for one or both of these.

HW (due Weds A, Thurs F)

Review your notes from the ripple tank lab.

Next, find some definitions for:

reflection
refraction
diffraction
interference

Consider these in light of your experiment notes/drawings - how do these definitions match what you saw?  What was happening in your experiment.

Please write down answers - I will be checking these in our next class.

Problems to try for F block - A block, read up on the Doppler effect

A police car traveling at 30 m/s has a siren that normally blasts a 1000 Hz tone.  Find the frequency you hear when:

A.  The car approaches you

B.  the car drives past you

C.  The car approaches you while you run toward it at 5 m/s

D.  The car has past you while you are running away from it at 5 m/s

Doppler Effect and more!

http://www.lon-capa.org/~mmp/applist/doppler/d.htm

http://falstad.com/mathphysics.html

Run the Ripple tank applet -

http://falstad.com/ripple/

The key in the Doppler effect is that motion makes the "detected" or "perceived" frequencies higher or lower.

If the source is moving toward you, you detect/measure a higher frequency - this is called a BLUE SHIFT.

If the source is moving away from you, you detect/measure a lower frequency - this is called a RED SHIFT. Distant galaxies in the universe are moving away from us, as determined by their red shifts. This indicates that the universe is indeed expanding (first shown by E. Hubble). The 2011 Nobel Prize in Physics went to local physicist Adam Riess (and 2 others) for the discovery of the accelerating expansion of the universe. Awesome stuff!

http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/

It's worth noting that the effect also works in reverse. If you (the detector) move toward a sound-emitter, you'll detect a higher frequency. If you move away from a detector move away from a sound-emitter, you'll detect a lower frequency.

Mind you, these Doppler effects only happen WHILE there is relative motion between source and detector (you).

And they also work for light. In fact, the terms red shift and blue shift refer mainly to light (or other electromagnetic) phenomena.

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More music-related sites, FYI:

http://www.youtube.com/watch?v=XKRj-T4l-e8

http://www.youtube.com/watch?v=cPALfz-6pnQ

https://www.youtube.com/watch?v=aWAjLOwOHU0

http://www.acs.psu.edu/drussell/Demos/TuningFork/fork-modes.html

HW

Read up about the Doppler effect for our next class.  Take notes.