Snell and Ohm

Physics participated in a lab today that examined Snell's Law. As was seen from the results, when light travels from a medium with a lower index of refraction to one with a higher index of refraction, there is a slowing down of the light that results in a new path of travel at an angle closer to the normal line than for the first medium. The reverse is true when light travels from a more dense to a less dense medium: light is bent away from the normal line. By measuring angles, you were able to calculate the index of refraction of the acrylic blocks and, further, to determine the speed of light through the block. Nor surprisingly, light slowed down when traveling through the acrylic. Tomorrow, we'll discuss this lab and examine refraction and Snell's Law more closely.

Honors Physics concluded their discussion of of lenses with a contrasting of convex and concave lenses and an examination of how object distance affects image properties for these lenses. Tomorrow, we'll look into total internal reflection, which will allow a review of Snell's Law, and dispersion. Friday - lab on lenses and image formation.

Physical Science spent time preparing for tomorrow's lab and reviewing/practicing working with Ohm's Law. Tomorrow's lab will have you experimentally explore Ohm's law and contrast ohmic and non-ohmic materials. At the start of lab tomorrow, we'll spend a bit of time making sure all groups understand how to wire their circuits and checking the circuits before data collection begins, but you should be able to puzzle things out fairly well after today's lab introduction. We'll explore circuits in more depth in the next section and examine more schematic symbols used to describe electrical circuits. There are many and may vary a bit with country and specific electronic fields, but here is fair sampling of the ones that are in common use. Note: you do not have to memorize this diagram. I'll point out which ones you should be familiar with for the MCAS exam.

Lots of Tru' Dat Out There Today

The Future

The Three R's

Reflection, refraction and resistance...those were the topics of discussion today. Physics completed their unit on reflection with a study of color and polarization. Tomorrow's lab will focus on Snell's Law and begin our study of refraction. Remember to read over the lab protocol and section 15.1 of the textbook to prepare for the lab investigation. Honors Physics was introduce to refraction and the basic properties of lenses. We will continue on with discussing the properties of specific types of lenses tomorrow and go over the lens calculations that you worked on today for classwork/homework.

Physical Science spent time exploring the property of materials to impede the flow of current - electrical resistance. The definition of resistance was examined, Ohm's Law was studied and factors affecting electrical resistance were described. Tomorrow, we will go over last night's homework and you will have time to further practice your math skills for Ohm's Law calculations. Thursday's lab will have students graphically and mathematically investigate ohmic and non-ohmic materials. To prove that I'm not making stuff up when I lecture, here is a table from an wire manufacturer website which lists resistance values for bare copper wire. Note that the resistance is listed per foot and at a specific temperature (resistance increases with length and temperature) and that it decreases sharply with increasing wire diameter. No, I don't know why wire with a higher gauge number has a smaller diameter. It is just one of those mysteries of life...Take time too, to browse around the site and look at resistance values for other types of metal wire. Note that the overall pattern for resistance variation holds for the different metals and alloys, but the individual values for resistance are different for each type of metal. There is other interesting information there, also. Tidbits about thermal conductivity, specific heat, density...all concepts that we have explored and that will make make a return appearance on the MCAS and class final exams.

BTW: a note for all sections. Although I encourage scientific thinking for all endeavors, as we all move towards and through the electricity studies, please make prudent decisions:

School: The Return

Surprisingly, most folks were actually awake and aware today! Physics completed their discussion of mirrors and will, tomorrow, take on color and polarization. Then, it is on to refraction with a lab exploring how the nature of the medium affects the degree of refraction. Snell's Law will be investigated and tested for acrylic blocks.

Honors Physics completed their polarization lab data analysis and went over the final discussion questions for the reflection chapter. Tomorrow finds us engaged with an introduction to refraction, the refractive index and Snell's Law. The next lab activity will center on concave/convex lenses and image formation.

Physical Science conducted a lab investigation on the structure and function of batteries. By testing various electrode combinations, students found that (a)swapping the positive and negative connections for the same electrode pair kept the same magnitude of voltage but changed the sign of the voltage and (2) the combination of carbon and zinc gave the highest and most stable voltage reading. In class today, some groups said that their best electrode combination was iron and zinc, but looking over your data, it was clear that carbon/zinc was the winner. We'll discuss this bit of information in class tomorrow prior to our exploration of resistance and Ohm's Law.

Vacation

See you tomorrow...

More Zombie Fun

The folks over at PopCap games have another promo for their upcoming Plants vs. Zombies game:

Zombie Maker

This is my first zombie:



I think I'll name him Clive...Plus, I am sure you want the .mp3 of that wonderful zombie jingle. Get the download here:

Zombies on Your Lawn

Note: right-click on the link and Choose "Save Target As." That will directly start the file download (make sure your browser is set to download files). Simply clicking on the link won't work.

Woe Be Unto Me

A very long day at the car dealership netted me a fixed car and an empty bank account. Here is a picture of what they had to replace (minus the steering column)...



...and here is a good link that explains how car steering works and what that pesky power-steering rack does that I can't live without:

HowStuffWorks - How Car Steering Works

Stuff to Do

It is vacation week. While I get the oil leak in my car fixed and have the burst pipe in my wall tended to, you guys do something interesting. Here are some options:

• The Museum of Science


• New England Aquarium


• MIT Museum


• MassAudubon Spring Vacation Week Activities

Read, watch some good television, do a bit of gaming...relax and come back ready to hit the books with a vengeance. The end is near!

Au Revoir...for a Week

April vacation is upon us and we greeted it with a deluge of lab work. 3 classes worked on polarization of light and 1 class worked with mirrors. Physical Science was the only class to endure a non-lab period, but they did receive their lab sheet for the lemon-battery lab that they will conduct the Monday we return. Our discussion centered on the nature of potential difference and how batteries maintain a potential difference to promote charge flow. We examined different types of batteries and described how a battery uses its stored chemical energy to increase the electrical potential energy of chages and move them to the high potential energy battery pole. We will review this after the lemon lab and continue on with our unit on electricity. Physics and Honors Physics will finish up with light by studying refraction and then jump, themselves, into the electricity unit. Hope everyone has a great vacation!

How Shocking!

Physical Science debriefed yesterday's static electricity experiment and further discussed the concept of electric discharge. Attention then turned to the idea of electric fields, electric potential energy and potential difference. Good time to drag out the ol' Tesla Coil for a demonstration. One day, I'll have to put together a set of photos of the puppy in action, but I doubt they'd come out as nice as this time-lapse image of a larger Tesla coil in action. Also, it lives in my classroom all year long - I should think about modifying it for a practical use, like these guys:



Physics discussed both plane and concave mirrors and were introduced to the techniques of ray diagrams and the mirror formula for analyzing situations involving reflection. Tomorrow, A block will conduct a lab activity on polarization and E block will get the opportunity to conduct their mirror experiment. The polarization lab will be conducted when we return from vacation, for E block.

Honors Physics finally got the chance to explore mirrors and image formation. Data was pretty good. The law of reflection held up well, with θI = θR in most cases (or at least close enough for government work). The distance required to read the eye chart in a mirror was 1/2 the distance required to read the same eye chart without a mirror, confirming that an image is the same distance behind a mirror as an object is in front of a mirror. If you could read a line at 2 meters without the mirror, you only had to stand one meter from the mirror to read the same line. 1 meter in front of the mirror + 1 meter behind the meter for the image equals 2 meters! The curved mirrors demonstrated the variety of images that can be formed through reflection by choosing the proper mirror and correctly positioning the object. Tomorrow - light polarization.

Happy Birthday Leonardo!

Today is Leonardo da Vinci's birthday. Now, there is someone who left his stamp on the world...here are some links to explore and learn more about his science, art and writings...

• MOS - Leonardo da Vinci


• National Museum of Science and Technology - Leonardo da Vinci


• The Leonardo Notebook

Physics completed their discussion of the properties of light and began to examine the phenomenon of reflection. We will conclude this discussion tomorrow and conduct a lab investigation on reflection on Friday.

Honors Physics discussed color and polarization. Color addition and color subtraction were contrasted methods to polarize light were described. Tomorrow, reflection lab. Friday, polarization lab.

Physical Science explored static electricity in today's lab activity. Charges were generated and the subsequent forces were used to influence the motion of matter. Tissue and aluminum foil flew, hair stood on end, balloons stuck to the ceiling...crazy stuff. Your lab questions bring up the concept of static discharge. The lightning and doorknob shock reference should give you a big hint about that concept, but do a bit of research if necessary. Tomorrow, we will further discuss static electricity, view a demonstration of static discharge and begin to move into the arena of electric current.

All Charged Up

Physical Science began its walk through electromagnetism today with the introduction of the concept of charge and the methods of generating charges on neutral objects. The ability of charge to produce electric forces was introduced and the use of Coulomb's Law to calculate the magnitude of electric force between two charged objects was discussed. You will get practice working with Coulomb's Law problems in class, so don't be worried if we seemed to move through the formula and concept rather quickly. Tomorrow in class, you will conduct a lab investigation that will focus on charge generation, the effect of electric forces on matter and the function of an electroscope.

A block Physics conducted a lab investigation on plane and curved mirrors. The basic properties of each mirror was examined and the law of reflection was quantitatively documented for a plane mirror. Tomorrow's lecture will continue through the properties of light and begin to look more closely at reflection and mirror types. E block lost its lab today due to an assembly. If there is time, we'll try and make up the lab at a later date, but time is growing short...

Honors Physics discussed the finer points of spherical mirrors and reviewed the use of the mirror and magnification formulas for evaluating mirrors. We didn't delve too deeply into ray diagrams, as we will spend more time with them when we discuss lenses, but you should be able to draw a basic ray diagram for a converging mirror forming a real image. Parabolic mirrors are not emphasized in this chapter, as their use in optics is rather limited, but where they come into their glory is with radiotelescopes (an EM wave is an EM wave) and for concentrating sunlight into a valuable and powerful source of energy. Here are a couple a videos on the use of parabolic mirrors for heating water. May seem minor, but consider that solar panels are extensively used to power household hot water heaters, and boiling water (steam) is the juice behind steam engines...

ACHOO!

Nasty, nasty cold has laid me low since Saturday but I am going to do my level best to finish off the week with vim and vigor. Word to the wise, though, don't get in sneezing range of me lest your April vacation be ruined by sickness. Writing my plans at the crack of dawn this morning, I think I got the day of rotation slightly mixed up and had the substitute pass out the lab sheets for Physical Science out today, even though your long block is not until Wednesday. My guess is that you guys figured it out, but just a note that we are not doing that lab tomorrow. Honors Physics - you'll do your lab during your next long block and we'll try to squeeze the light polarization lab in during a short block. Physics - you'll be working on the mirror lab tomorrow. I mixed up the day of rotation, so you didn't get your lab sheets today, but the lab is simple to execute and doesn't require signficant advanced reading.

Wrapping Up the Week

Since tomorrow is a half day, I'll consider the week 95% over and make myself happy...

Honors Physics discussed the properties of plane and concave mirrors and the utility of the mirror formula. C Block will continue this discussion tomorrow and add convex mirrors to the mix. G Block does not meet tomorrow, so will rejoin the unit with the lab activity on mirrors scheduled for Monday.

Physics conducted the light intensity lab and, again, witnessed a very good inverse-square relationship between distance and brightness. Adding sunglasses did not alter the inverse-square relationship - it only dropped the values of the curve. Again, all sunglasses tested today demonstrated UV resistance in the presence of sunlight. A block will discuss the wavelet theory of light tomorrow and E block will have to wait until Monday for that bit of information.

Physical Science reviewed for tomorrow's exam. Tomorrow, I will collect the homework we went over, so have it ready to turn in. Some folks were having a spot of bother with harmonics; here are some links to harmonics resources:

• Strings, Standing Waves and Harmonics


• Fundamental Frequency and Harmonics


• Harmonic Series


• Standing Waves Applet - this applet shows the resultant wave pattern in a string, pipe closed on one end and pipe open at both ends. The relative intensities of each harmonic can be varied to see the effect on the resultant wave pattern.

Here is a nice series of videos detailing harmonics and harmonic series:

While I Toil ...

...my dogs are partying away. Doesn't quite seem fair. Here is some footage of them today at their beloved Bitti's daycare with their canine companions:

Sunglasses at Night

Honors Physics investigated the inverse-square nature of wave intensity/source distance to very good result. Added on was a study of how well sunglasses reduce light intensity. It was quickly apparent that some types of sunglasses do a much better job at reducing the amount of sunlight that reaches the eye. This experiment did not include a side dish of polarization; we will conduct a separate lab investigation on polarization at the end of the chapter. G block added an extra component to the lab that targeted sunglasses ability to block UV rays. An apology to C block, who did not conduct this part of the lab as I had forgotten that I had gotten a free sample of UV-sensitive beads thrown in with a purchase until I ran across them at lunchtime. Today, UV protection is standard for sunglasses and all the tested pairs blocked the UV rays from the test beads. Older sunglasses might likely not block the UV, however, so take care when purchasing vintage sunglasses that you actually plan to wear outdoors.

Physics discusses the nature and models of light. Tomorrow, you will conduct the intensity lab and are reminded to bring a pair of sunglasses with you to class tomorrow. We went deeper into the particle model of light than does your textbook in this chapter and don't forget this when test time comes around.

Physical Science completed their discussion of sound and light with an overview of lenses and the phenomenon of dispersion. We will review the last of the homework problems tomorrow before engaging in a general review of the chapter. The test of Friday will be longer than normal due to the fewer number of math problems. The only formulas we worked with in this chapter were the wave speed formula, the intensity formula and the lensmaker's equation (from the lab. The law of reflection does not really count as a formula, so I'll won't put it on the list. There is a lot of material in this chapter, so I hope that no one leaves their studying until the last minute. Monday - we begin our unit on electricity.

Today's discussion of rainbows brought up the concept of moonbows:



Here is another interesting formation- the double rainbow. Note the color order of each member of the pair:

Bill Nye on Light

Here's a bit of Bill Nye on light and optics:

Red Sox Season Opener

This will be quick as the game is consuming my attention. Physics took their sound exam and will begin their investigation of light tomorrow. Honors Physics was introduced to light today and tomorrow's lab will center around the inverse-square relationship associted with light intensity and source proximity. Physical Science conducted an investigation on image formation for convex lenses. The lensmaker's formula was examined and used to make meaning of the lab data. The concept of magnification was introduced by having students measure image and object heights and compare their ratio when object/image distance was varied. Tomorrow - a continuation of refraction. Sound and light exam on Friday. Ciao!

Moving Into the Light

Honors Physics took their Sound exam today and will begin discussing the fundamental properties of light tomorrow. The first section of this chapter should be something of a review, as we touched on a lot of the information during our general overview of waves. The next section will center on mirrors, where we undertake to dissect the refelction process and how plane and curved mirrors form images.

Physical Science began a discussion on refraction today. Light is not the only wave that undergoes refraction, but it is the most prominent wave type whose refractive properties are put to good use. Tomorrow's lab will center on one use - lenses. You will investigate how a double-convex (converging) lens forms images and how proximity of lens to object influences image formation. When we finish this chapter, you will have more MCAS practice. You'll get to work through electromagnetic radiation and waves questions from prevous MCAS exams, as you have for previous topics. Remember, June is coming...although we'll do a brief review before the MCAS, you should not put off preparing for the exam until the last minute. We will be covering new information almost to the day of the test, so start independently reviewing the material and getting extra help as needed.

Physics conducted a lab on sound waves and the formation of beats. It was a good lab to review the basic features and properties of sound waves (in preparation for tomorrow's exam) and to illustrate beats and beat frequency. It was also nice to, again, see how a general equation (sine function) contributes to the understanding of real physical phenomena. That the various parameters of the function have a real-world meaning are sometimes lost unless you get to actually use the equation in lab. Data for the lab was quite good for all groups. Calculated beat frequency matched the beat frequency established by the choice of test tones; the individual tones produced well-formed sine curves that accurately predicted the frequency, period and amplitude of the wave; the physical appearance of the beats closely matched the diagrams discussed in lecture. Be ready for tomorrow - your last bite at the sound apple. Then, it is on to light...

PopCap Games

I am a big fan of PopCap games. They are cheap, give you a license for 6 computers and the games are addictive. Peggle, Peggle Nights, Bejeweled 2, Bejeweled Twist, Bookworm Adventures...these and others are always on my computer. They have a new game coming out soon and produced a music video for it. Thought you'd like to give it a look-see:

There's Nothing Worse Than a Sick Dog...

...unless its TWO sick dogs. Although anything serious was ruled out by the canine medical professionals, that did not alter the fact that my pooches were miserable from well before dawn until, well, now. They got some quality medication for their upset tummies and to kick-start their desire to nap, but it has not been a fun day.

Perkunas just gazes balefully at me:



Rodney is keeping his distance until he is sure there are no more vet visits in his future:



It is a lot of work taking care of a sick kid, even one of a different species, so make a point to do something nice for your caregivers tonight. Just think about all the stuff they've had to clean up since you were born...

Harmonics

Physical Science engaged in a lab investigation on mirrors and image formation today. It was easily seen how different mirrors produce different images - both in type and magnification. One section of the investigation had students confirm the law of reflection for various viewing angles with a plane mirror. Sure enough, no matter the viewing angle, the incident angle and reflected angle were the same. Tomorrow, we'll discuss reflection and color and go over the homework. Starting Monday, attention turns to refraction. Expect your exam towards the end of next week.

Physics spent their time discussing the nature and production of harmonics by musical instruments and the voice. Inharmonic and harmonic overtones were contrasted and the importance of harmonics to music was emphasized. Attention then turned to the nature of beats and how they could be used to determine how well an instrument was in tune. Honors Physics had this discussion yesterday and will do a lab on this material tomorrow. Today was set aside for them to review for Monday's exam. Physics will have their review tomorrow and conduct their lab investigation on Monday. Here is a nice video about guitar harmonics that includes how they can be intentionally and preferentially formed:



Here's another about how guitar strings are made:



Harmonics for a piano:

April Fool's Day!

Physics conducted their tones/overtones lab today and the results were very good. Tomorrow's discussion of harmonics will give more context to the overtone idea and classify harmonics as a subset of overtones. We'll discuss why different instruments have characteristic sounds and also examine the concept of beats. Beats and beat frequency will be the focus of Monday's lab. Friday - review day. Tuesday - Exam.

Honors Physics ended their sound unit with an overview of harmonics and their role in determining sound quality and uniqueness of sound. We review tomorrow, conduct the beat/beat frequency lab on Friday, exam on Monday.

Physical Science had a discussion of reflection and color today, with a solid overview of types of mirrors and the images they form. Plane mirrors: virtual images, same size/distance and orientation as object. Diverging mirrors: virtual images and can magnify objects. Converging mirrors: real and virtual images (depending on object distance from mirror surface) with varying degrees of magnification. Students will explore these mirror types and their reflective properties in tomorrow's lab. Remember though - all mirrors are bound by the law of reflection (θ_I = θ_R). We also discussed color and contrasted color addition and color subtraction. Both work to give us the variety of colors we see, but accomplish it through different methods. After reflection, we'll sally forth into refraction and dispersion before ending our unit on light.

As today is April Fool's Day, here's a link to the best April Fool's hoaxes ever perpetrated:

Top 100 Hoaxes

The #1 hoax - The Swiss Spaghetti Harvest - is a classic. First broadcast by the BBC on April 1, 1957, the result was the same as for the the War of the Worlds hoax on October 30, 1938 - people actually believed it! Here's some footage- it is still used today to highlight the properties of "documentaries" that contribute to their believability and how those properties can be turned to less honorable purposes...