When using the Vernier microphone to measure sound waves, the result is not always a nice-looking sine curve in Logger Pro.  For example, the graph of the sound wave produced by a 880 Hz tuning fork when data is collected at 10000 samples/second is shown below. This almost looks like a smooth sine curve, but has some sharp edges at the troughs and peaks. Is it possible to get better results?

Will increasing the sampling rate improve the results?  Surprisingly, if the sampling rate is increased, every data point is doubled, producing a graph that appears to have steps in it. Below is the graph of the sound wave produced by the same tuning fork, but with the data collection rate set to 20000 samples/second. According to the data table in Logger Pro, pairs of identical pressure values occur 0.00005 seconds apart.

How can students measure these sound waves and get results that more accurately reflect the nature of the sound wave?

Tip #1: Do not use a sampling rate higher than 10000. Keeping the sampling rate at 10,000 prevents the strange doubling of data points, which is the cause of the steps in the graph.

Tip #2: Remove the lines connecting the data points;  fit a sine curve to the data. Thanks to Vernier support for this suggestion! 

The steps to accomplish this are:

1. Removing the connecting lines: Select the graph, then go to the Graph menu, and select Graph Options. Choose the Graph Options tab, and then de-select “Connect Points,” and click OK. The result at this point should look something like this:

Note: Initially, when you remove the connecting lines, the graph may appear to be a chaotic jumble of data points with no apparent pattern, but by changing the time-axis to a short enough time interval, you will once again be able to see the sine-wave shape of the individual data points.

2. Fitting a sine curve to the data: Click on the “curve fit” button, and select the Sine function. Click “Try Fit” and “OK.” The graph should now look like this:

As I begin to have students work with Arduino circuit boards, it seemed prudent to review the ways these circuit boards can be damaged. I found the article “10 Ways to Destroy an Arduino” by Ruggeduino to be very helpful, as it explains what kinds of connections will damage an Arduino and explains why, complete with circuit diagrams that show the path which current will take.

A Portland General Electric customer asked the company this question, and the company decided to explore the possibility. What do you think? What would be needed to make this possible?

Watch this 2-minute video as PGE’s director of Technology Strategy, Dr Conrad Eustis, explains his findings.

Do all red-green bicolor LEDs have the same internal connections?

In preparation for designing an emergency flashlight this week, my students investigated the direction that charge can flow through various kinds of diodes: an LED that emits white light, a Bicolor LED that emits red or green light depending on the direction that charge travels through it, and a rectifier diode.

Last year for this investigation, we used the Radio Shack Bicolor Red and Green LED (Model# 276-0012), but this year I needed to replenish my supply and found that Radio Shack no longer carries this part. At Oregon Electronics, I found bicolor LEDs and assumed they would have the same internal connections. Wow, was I wrong! Not a big deal now that I know what’s going on, but my erroneous assumption caused me a great amount of confusion and wasted time because I was using the color of the light emitted to deduce the direction of charge flow in an electromagnetic induction application.

The internal connections for two different bicolor LEDs
Inside of a bicolor LED, there are two different-colored LEDs connected in parallel but with opposite polarity.

• When charge flows (conventional current) from the long lead to the short lead of the Radio Shack LED, it will emit GREEN light.
• When charge flows from the long lead to the short lead of the Oregon Electronics bicolor LED, it will emit RED light.  What a surprise!

Lesson learned: Internal connections of bicolor LEDs are not standardized. Always test new bicolor LEDs to discern the internal connections.

A fiber optic cable must have a core that is more optically-dense than the layer surrounding the core (the cladding.)  If the light is traveling inside the core and hits the boundary between the core and the cladding, it can completely reflect from that boundary instead of passing through the boundary and out into the cladding.  When this happens, the light will bounce back and forth inside the core, even traveling around curves! This process is called “total internal reflection.”

Total internal reflection can be observed by making a “fiber optic cable” out of Jello. Jello is more optically dense than air, so the Jello will be the core, and the air surrounding the Jello will be the cladding. By aiming a laser pointer into the end of the Jello fiber optic cable, you can find some angles of incoming light that will produce total internal reflection. (It helps to do this in a darkened room.)

Although a strong beam can only be seen for a few reflections, the fact that the end of the “cable” is so bright indicates that most of the light has stayed inside the cable, traveling all the way to the end by total internal reflection.

Recipe for making a Jello Fiber Optic Cable

Ingredients

• 2 small packets unflavored Gelatin
• 4.5 ounces Lemon Jello (from a 6 oz box)
• 2 cups boiling water

Directions

Mix all ingredients together until powders are completely dissolved. Pour into a 9×13 Pyrex dish and refrigerate until firm.  Cut into strips, about 1 cm wide, avoiding areas where the Jello is curved due to the shape of the Pyrex dish.

Certain materials will emit visible light a short time after absorbing ultraviolet light. This process is called fluorescence.  Ultraviolet light has a shorter wavelength than visible light, and our eyes are not capable of seeing ultraviolet light. We can see the emitted light because it has a longer wavelength and is in the part of the spectrum that our eyes can detect.

Our family recently visited the Rice Northwest Museum of Rocks and Minerals in Hillsboro, Oregon, and I was fascinated with their display of fluorescent minerals!  It is really a sight to see. Had I known what treasures filled this museum, I would have visited years ago. (You can even save on admission by picking up a Cultural Pass at the library.)

Minerals in normal lighting

Minerals emitting visible light after absorbing ultraviolet light

The lighting on the minerals automatically alternates between normal room lighting, long wave ultraviolet light, and short wave ultraviolet light, so it is easy to compare the appearance of the minerals in each type of light.

This excellent photo showing a variety of colors being emitted is from Wikipedia.

I recently received a free SpillNot through a promotion at Arbor Scientific. This really is a cool tool!  With this device, you can carry a beverage or even swing it around in circles without spilling!  It’s a great illustration of the effects of horizontal vs perpendicular acceleration on a cup of liquid and the physics of circular motion. Click on the link to see a video of the SpillNot in action and read an explanation of the physics behind it.  My children were fascinated with this cool tool, though I have to admit that we did have a spill!

I think it must be a uniquely human experience to contemplate and be awed by the vastness of the range of sizes of things in our universe. The two excellent resources mentioned in this post provide an opportunity to get a sense for this range. As I view them, I alternate between feeling very, very small when zoomed out to the scale of galaxies and feeling very, very large when zoomed in to the scale of atoms.

Powers of Ten is a classic film. As stated on the opening screen, “It is a film about the relative size of things in the universe and the effect of adding another zero.” The film begins by focusing on the scene of a picnic in Chicago, showing the size of a 1-meter by 1-meter square. Then every ten seconds, the view zooms out to show an area that is ten times larger than before. After zooming out past the Virgo cluster of galaxies, you are returned to the scene of the picnic where now you zoom in every ten seconds to see an area that is 10 times smaller than before until finally reaching the nucleus of a carbon atom.

The Scale of the Universe 2 is an interactive interface that allows you to explore the sizes of things on your own. You can zoom in and out to see things of different sizes, and if you click on an object a little information box pops up. How do Pluto and the United states compare in size? What is Gomez’s Hamburger, and how big is it? What is thinner – a piece of paper or a human hair? If you read the information boxes, you’ll find that the authors have a sense of humor –for an example check out the water molecule. There is truly a wealth of interesting information and comparisons to be discovered here. Enjoy!

When children are taught how to do science inquiry, the process usually begins with an inquiry question followed by having the student make a prediction about what is going to happen.  This approach often continues through high school lab science courses, even though in these inquiry situations students often do not have very much prior knowledge to base their prediction upon.

Having students make a prediction before doing the experiment certainly increases student engagement because they want to find out if they were “right,” but there are some drawbacks to this approach. One is that students who make a prediction that turns out to be “wrong” can feel a sense of failure. If a student repeatedly makes wrong predictions, she may develop a belief that she is not smart enough to do science or that she is not good at science.  Students often do not have any real background knowledge of the phenomena being investigated, and so their sense of success or failure hinges on how lucky they were at correctly guessing the outcome of the experiment.  A second drawback to having students make a prediction before carrying out an experiment is that it can skew their observations; what they expect to see can affect what they actually do see.

Investigative Science Learning Environments (ISLE) uses a different process to avoid these problems.  The ISLE process starts with an observational experiment in which students make observations or collect data without a prior expectation about what will happen. From these observations and data, students look for patterns and come up one or more possible explanations, or hypotheses, that answer the questions “why” or “how”. These explanations need to be experimentally testable. The next step in the process is designing an experiment to test each explanation.  Only at this point do the students make a prediction, which is based upon the explanation.  Because the prediction is based directly on the explanation, it is the explanation that will be found to be right or wrong, not the student. In this case,  the correctness of the prediction now reflects upon the correctness of the explanation, not the on the student personally.  The experiment becomes a judge of how well the explanation fits the real world, not of how smart the student is.  A prediction that turns out to be wrong can actually be exciting because it means that the there is something more to discover.

I really liked this approach, but thought there still was some value in having students give some initial thought to what would happen in an experiment, even when they don’t have very much to base it upon.

This month, at the Oregon AAPT meeting, Bradford Hill gave a presentation entited “Engaging Students through a Patterns approach to Physics.”  His approach is to call the initial prediction a “wild guess.”  The wild guess prediction is followed by inquiry to collect data, find a pattern, and then making a “Data-informed prediction” for a situation.  This draws the students’ attention to the fact that our confidence about a prediction can vary, and that the the quantity and quality of data used to determine the pattern impacts the confidence that can be placed in the prediction that is based on the data.   Calling the first prediction a “wild guess” frees the student from feeling that its correctness is a reflection of their intelligence or ability to do science.

The game “Operation” utilizes a simple electrical circuit to create an entertaining and challenging game. If the tweezers touch the metal surrounding the cavity holding the body part to be removed, a loud buzzer sounds the the little man’s nose lights up.  Students can use their understanding of direct current circuits to figure out the circuit components and draw a schematic diagram showing their connections.

Hyperdash controller and target disks

Another game that has some interesting switching to figure out is HyperDash.  This game consists of a hand-held controller and five target disks. When the game begins, the controller calls out a color or number, and the player has to find the target and press the controller down onto the target. Somehow the controller “knows” whether you hit the right target or not.  How can it tell?

View of the bottom of the controller

On the bottom of the controller, there are three “buttons” that can be compressed.  How could three buttons be enough to identify five targets?  Are all the target shapes the same? What do you notice about the placement of the buttons on the controller?