Lab notes

How does the object location affect the formation of images, in terms of:

-          Whether or not an image forms

-          Whether the image is “real” or “virtual”

-          Whether the image is larger, smaller, or the same size as the object

-          Whether the image is upside-down or right-side up

-          Where the image is located

First, find an approximate “focal length” (f), using the technique described in class – focusing on a bright object outside, bringing an image onto a screen.

Then, data collection begins.  Do the convex lens first.

In this lab, move the object (candle) around methodically.  Note the following in a table:

do           object distance from lens

di            image distance from lens

U/D        up or down

R/V        real or virtual

Size        size change

Repeat for a concave lens.

Pre-Lab

As you saw in class, convex and concave lenses behave in different ways.  In our new formal lab, you will determine exactly how this happens.

Prior to this, research this question - what exactly is a focal point, and how is it different for a convex lens vs. a concave lens.

In the lab, you will be moving an object (candle) and seeing how images form (if indeed they do) - are they larger/smaller/same, real/virtual (look this up, too), upside-down or right-side up.

HW

E -- do as earlier listed

A -- Problems to try:

Light passes from air to a block of new stuff, with the angle going from 60 degrees outside the block to 35 degrees inside the block.  The angles are measured with respect to a normal (perpendicular) line.

a.  Draw this.
b.  Calculate the index of refraction of the stuff.

c.  Find the critical angle of this stuff.

Applet to play with / HW

http://stwww.weizmann.ac.il/lasers/laserweb/java/twoangles2.htm

Also (E block) -- calculate the index of refraction from today's experiment.  Look up the value of n for water (or salt water).

Play with the applet, too.

And if you're really, really bored:

http://www.slate.com/articles/arts/culturebox/2013/11/where_s_waldo_a_new_strategy_for_locating_the_missing_man_in_martin_hanford.html

Doctor Whoooooooo?

http://geekdad.com/2013/11/doctor-timeline-fifty-years-glance/

Purely for Doctor Who fans.  For the rest of you - sorry.

HW

E block - When last we met, we were chatting about total internal reflection.  Use Snell's law to derive an expression for the critical angle of a material.  Assume that light comes from inside the material (say, water, though you can just call it n1) and goes to air (n2 = 1).  This will be a simple expression.

E and A:

Read about fiber optics and see how is is related to total internal reflection.

Find out how you get your phone/cable/internet service in your home (if you get it).

Problems:

1.  What is the critical angle of a material with index of refraction 1.6?

2.  Can you make a general expression for critical angle, one that represents light traveling between any two mediums?  That is, assume that the new medium is NOT air, but rather some stuff with index n2.

Snell's Law homework

1. Review the derivation.

2. Solve these problems:

A. What is the index of refraction for a material in which light is slowed to half its speed in a vacuum?

B. Water has an index of refraction of 1.33. What is the speed of light in water? (Water you waiting for?)

C. Light passes from air to a piece of plastic, with an initial angle of 50 degrees and refracted angle of 30 degrees. What is the index of refraction of this plastic?

D, A material has an index of refraction of 1.7. Light is refracted at an angle of 44 degrees inside the material. What was the original angle outside the material?

HW

Look up two things:

index of refraction
Snell's law (of refraction)

Both will have equations associated with the definitions.  Figure out what you can.

If you're feeling ambitious, look for a derivation of Snell's law.  You may not be able to follow it, and that's quite ok; however, if it's the geometry version, which we'll cover next class, you may want a heads-up on it.

Doppler applets from class

http://falstad.com/ripple/

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

practice pre-test problems.

Remember:  Proper prior preparation prevents poor performance.

1.  B is 466.1 Hz, approximately.  Find the following frequencies:

a.  the next 2 octaves
b.  the 2 octaves below
c.  the C above (one semi-tone)
d.  the D above (3 semi-tones)

2.  Write your own Doppler effect problem and solve it - be sure to have a few different conditions.

3.  Consider a tube open on both ends, 0.4-m in length.  Find the relevant stuff for the first 3 harmonics:  wavelengths, frequencies, shapes.  Repeat for the same tube open on one end only.

4.  Graph the following:  y = 3cos(2x) - 5sin(3x).  Find the y value at x = 75 degrees.

5.  Review the speed of sound lab in your notes.