Example

Dress Rehearsal

You are in your electronics class, and your instructor has just introduced “Ohm’s Law.” The first time you ever heard that word was when your out-there English teacher wanted to meditate during eighth hour. Later, you heard it in a conversation about college basketball…the legendary Katie Ohm from the University of Minnesota.

But this is something entirely different. Your textbook notes that Ohm’s Law describes the relationships among electric current, voltage, and resistance. Ohm’s Law states that current flow in an electrical circuit is proportional to voltage and inversely proportional to resistance. What does this mean? Your text explains that that the amount of current flow in a circuit depends on how much voltage or resistance there is in the circuit.

Still, unless you understand certain words in these sentences, your understanding of what you’ve read is limited. These are called “domain-specific” words. Here, they are specifically used for concepts involving electricity. Let’s deconstruct the sentence. You know that current, or flow of charged particles, electrons and neutrons, is responsible for the production of electricity. Now add these key terms: voltage is the push or pressure that moves the current; resistance is what slows the current.

Did you catch that? Here’s more…

Next, your text establishes certain rules about the law. There are two general rules. Rule number one states that, if the resistance remains the same, as voltage increases, current increases, and as voltage decreases, current decreases. The second rule is that, if the voltage remains the same, as the resistance increases, current decreases and as resistance decreases, current increases.

Why don’t they just say so?

All of this can be symbolized by an algebraic equation in which “E” stands for the electromotive force of voltage. “I” stands for intensity, or amperage. And, “R” stands for resistance, or ohms. These terms are defined in the text. They are, again, domain-specific. The equation looks like this: V = IR.

Your instructor advises you that if you know two parts of the Ohm’s Law equation, you can easily calculate the third. He means that to determine volts, multiply amps times ohms. To determine amps, divide volts by ohms. To determine ohms, divide volts by amps. That process looks like this:

Understanding basic concepts is much easier when you understand the vocabulary and symbols used by authors. And that results in mastery of the material, better grades, and higher scores on state tests. Ohm-my-gosh!

Source:

Electrical/Electronic Stage 1. Michigan: North American Operations, 1998.

Freeman, Ashley. “Ohm’s Law.” The Science Learning Community. 2011. Tritec. Inc. 11 May 2012. http://www.tritec-inc.org/science-units/physics2011-electricity/lesson-freeman.html.

Drill

Read and use the information in the following passage to fill out the chart. Use context clues whenever you can and a dictionary when needed.

Astronomical tables dating to the golden age of Maya civilization have unexpectedly come to light on the walls of a roughly 1,200-year-old room in Guatemala.

Hieroglyphs and numbers painted on the stucco walls of a structure built during the Classic Maya civilization record cycles of the moon and possibly Mars, Venus, and Mercury, according to Boston University archaeologist William Saturno and his colleagues. Excavations in 2010 and 2011 at Xultun, a Maya site first described in 1915, revealed that painted murals once covered three of the room’s inside walls and its vaulted ceiling.

The researchers report that until now, Maya astronomical tables were known from bark-paper books — known as the Dresden Codex — created 400 years or more after the ancient civilization’s demise around 900.

“The Xultun finds provide the first direct evidence of astronomical information from the summit of Maya glyphic literacy, the Classic period,” remarks archaeologist Stephen Houston of Brown University. He calls the recording of astronomical tables on walls rather than in a book “baffling, even astonishing.”

One Xultun wall section contains bar-and-dot numbers in columns that resemble astronomical tables in the Dresden Codex. Moon hieroglyphs appear atop at least five columns. These tables record lunar months, in six-month sets, over roughly 13 years. The number 13 held special significance for organizing the Maya calendar.

“It’s as though someone today took a university textbook and painted it on a wall,” says archaeologist Charles Golden of Brandeis University in Waltham, Mass.

Similar numerical records at Xultun and in the Dresden Codex suggest that the Maya passed on and revised astronomical information over many generations after the Classic collapse, Saturno says.

A table of solar and lunar eclipses in the Dresden Codex starts in the mid-8th century, indicating that the document was based on information from at least 50 years before the Xultun finds, anthropologists Harvey Bricker and Victoria Bricker, both of Tulane University in New Orleans, wrote in a joint email.

Referring to Dresden Codex calculations of a starting time for astronomical tables, the Brickers say that corresponding numbers at Xultun record a period of almost exactly 198 eclipse seasons. Each 37-day eclipse season contains at least one solar and one lunar eclipse.

“Ritual specialists at Xultun, like the authors of the Dresden Codex, were concerned not only with the moon’s monthly cycle but with the much longer cycle of solar and lunar eclipses,” the Brickers conclude. So the Xultun Maya used walls as scratch pads to construct astronomical records, the Brickers suggest.

A plaster bench in the Xultun room, resembling benches Maya rulers used at royal court meetings, sits in front of a painting of a king talking to a kneeling attendant, says archaeologist David Freidel of Washington University in St. Louis. Classic Maya vases show similar court scenes, sometimes with humans and gods writing on tablets, Freidel says. No pottery depictions of anyone writing on walls have been found.

Source:
Bower, Bruce. “Maya Wall Calendar Discovered.” Science News. 10 May 2012. Society for Science and the Public. 10 May 2012. http://www.sciencenews.org/view/generic/id/340589/title/Maya_wall_calendar_discovered.

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