Here’s what we’re going to do today:

• agree on what’s going to be on the final
• Quick lesson on percentages
• Resistor Codings
• Review homeworks

First, we will look at percentage problems. Then, we will apply percentages to a common application in the trades: tolerance. When you buy a box of nails that says it has 200 in the box, and it actually has 201 or 199 nails, the tolerance is ±1 nail. For resistors, tolerance is expressed as a percentage.

Calculating a resistor’s tolerance is another 3 step process:

1. Translate the Band Colors into numbers. Use this link to open a resistor band conversion pdf:
   
   Band Colors
   
   Notice that there are 4, 5 and 6 Band resistors. All of the resistors in the above graphic on this page are 4 Band resistors. The first resistor in the pdf is also a 4 Band. In a 4 Band, only the first two colors are the resistance values in ohms. 5 and 6 Band resistors have three numbers for resistance. So the first resistor in the pdf has a Red and Green, or 25.
2. Apply the Multiplier. Now we “move the decimal” just like we did for metric unit conversions. I organize the 3 Steps with a
   
   Worksheet
   
   The next Band is called the Multiplier. Just like a metric prefix (kilo, milli) can move the decimal left or right, so to can a Resistor Band Multiplier. In our 4 Band resistor, the next color is Orange, which means our Multiplier is +3. So our resistance value is now:25 × 10⁺³ ohms. All a positive 3 means is that you are going to move the decimal 3 places to the right, making our resistance value 25,000 ohms.
3. Calculate the Tolerance. Now that we know what the resistance is supposed to be, we can apply the Tolerance value to figure out the + and −, like we did for the extra or missing nail. In our example, the last color is Gold. Notice that White, Gold and Silver colors are outlined in black to distinguish them from the other colors. In an actual resistor, you won’t see black outlines. Gold means a tolerance of 5%. Here’s the calculation we have to do:
   
   5% × 25,000 = 1,250
   
   That means the actual resistance value is between 23,750 ohms and 26,250 ohms.

Let’s practice some more …

Practice Worksheets

Tomorrow (no class) is my next data dump day (after 5PM), so today’s the last full day of instruction for this course. Friday, we will review this week’s homework, and some light instruction and touchups. And next Monday is our last class, when we take the final.

Today, we will explore the following topics:

• Geothermal pump calculations
• Metric and Imperial Units
• Percentages

Breakout Geothermal Pump

Answer Keys

Blueprint Shanty Reports

Heat Transfer (U factor)

A major part of my professional development has come from kicking back at the end of a work day, and reflecting upon what what went well, and more importantly not, and wonder why.

My biggest mistake, yesterday, was not saying thank you, (diolch in my native tongue), to those of you who corrected errors in my answer key. We all learned something yesterday.

Teaching would be an easy career if every day was a Friday. Today, all of the work is on you – here’s the rubric:

• +/– Feet & Inches (8 questions)
• Missing Sides/Perimeter (6 questions)
• Ruler Measurements (8 questions)
• More/Less Than (8 questions)
• Nail/Screw (8 questions)
• Carbon Footprint (8 questions)

46 Questions

1. You’ll look over your assessed homework (except nails & screws)
2. Into the shanties, to practice nails & screws
3. Then we’ll revisit the homework
4. If time permits, we will look at a new topic, that WILL NOT BE on the midterm.

Note: If you want to resubmit a homework NO PROBLEM.

answer key