Math 63Resistor Activity Name: _______________________________Here are some web sites that offer great explanations of what resistors are and how they are used.

1) http://www.youtube.com/watch?feature=player_embedded&v=VPVoY1QROMg

2) http://www.doctronics.co.uk/resistor.htm

3) http://www.youtube.com/watch?v=TZYlPQU9B4M

4) http://www.the12volt.com/resistors/resistors.asp

5) http://www.allaboutcircuits.com/worksheets/resistor.html

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When I viewed this video for the first time, I thought it was kind of geeky and boring, until I got to the cool little experiment at the end on homemade resistors. I now really like this geeky looking guy and think the site is terrific. Click on the link or do a search for MAKE presents: The Resistor.

Lots of really good information here, easy to understand, and it includes some cool links including a color code converter (which is a really nice way to check your “color code math”).

This website was one of if not the best. You could spend hours here. It includes worksheets and ALL levels of detail about electronics. I HIGHLY recommend this. You could spend days/weeks on this.

This site includes a color code calculator! This is great for practicing how to use the color code chart and checking your answers – I used this one a LOT!

This site is not as exciting as others, but it does show how to use the multimeter. It also has a short demo on lighting up an LED and then showing the effects of using a resister.

6) http://www.article19.com/shockwave/oz.htm

7) http://www.youtube.com/watch?v=bF3OyQ3HwfU

PART 1Before we start the “hands on” part of the activity, let’s review some basic information.

A resistor is one of the basic types of electronic components. Resistors have two terminals and a semiconductor, such as carbon, in the middle. A semiconductor is just what it sounds like: something that conducts electricity but not that well. While conductors like copper and gold are used in circuits to let electricity flow freely, a semiconductor is used to provide some resistance to the flow of electricity. That is why a resistor has that name.

When electricity flows through the semiconductor, some of it is turned into heat. The higher the voltage, the higher the energy is.

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I liked this website because it was interactive. It would be great for the student who already has some knowledge of electronics or for the student who has the initiative to learn new things using interactive websites.

http://www.circuitstoday.com/working-of-resistors

http://speakerbug.com.au/shop/index.php?main_page=index&cPath=16_5

http://mf-powerresistor.com/rr_pw.htm

This is a nice little video on how to do the basics on a multimeter. I wish I had watched it before I got going. It is definitely worth 4 minutes and 36 seconds of your time.

In most circuits, this heat is just wasted energy that is cast aside or is blown away with a fan. In some devices, however, the heat produced by the resistor is the main purpose of the circuit. Electric stoves, for example, use large resistors to produce a lot of heat to cook your food.

Electricity is measured in voltage (V) and amperage (A). The voltage can be thought of as the pressure of the electricity, and the amperage as the amount of electricity flowing through the circuit. Voltage, amperage and resistance are related by the equation V = IR (voltage equals amperage times resistance). At a set voltage, amperage gets lower as the resistance gets higher.

If you think of a circuit as pipe carrying water, it's easy to understand why resistance lowers the amperage. If you put in narrower pipes without changing the water pressure (voltage), it will decrease how much water can flow through the pipe at one amperage.

The information above was taken from http://www.ehow.com/how-does_4597224_a-resistor-work.html

Three more things to keep in mind:

1) Ohm’s Law says: Voltage (volts) = Current (amps) * Resistance (ohms)

2) If the voltage goes UP and the resistance stays the SAME, the current must go UP.

3) If the voltage goes DOWN and the resistance stays the SAME, the current must go DOWN.

Our activity is going to begin with a homemade resistor.

Materials you need1. Multimeter with 2 connectors, one going to the negative/black port in the meter (it should say

COM) and one going to positive/red port in the meter (it should have an ohms symbol ).2. Paper3. Pencil (preferably #2)

We should have plenty of meters so you each can work with one. I want you to work together. That means you help each other, but every person does their own thing. Each of you will turn in your own paperwork. Make sure EVERYTHING in the packet is filled in.STEP 1:

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V = I * RDecrease

V = I * RIncrease

Watch the video with the geeky guy. http://www.youtube.com/watch?feature=player_embedded&v=VPVoY1QROMg

We will follow the same instructions shown in the video by doing the following:

STEP 2:In the space below, using your #2 pencil, draw a bar 3 inches long and about ¼ inch wide (mark it at ½ in, 1 in, 2 in, and 3 in. Fill it in with your pencil and make it as dark and shiny as possible.

STEP 3:Take measurements of your homemade resistor as shown in the video by sliding one probe back and forth along the bar while keeping the other in place. See how your results compare to other students. Pay close attention to the units.

Be mindful of the units on the meter.Units on the multimeter may or may not be shown on the readout; they may be indicated by the dial setting.

RECORD YOUR RESULTS IN THIS TABLERecord the multimeter

reading at 3 inches(the connectors are

furthest apart).

Record the multimeter reading at the

2 inch mark(2nd furthest apart).

Record the multimeter reading at the 1 inch

mark.

Record the multimeter reading at the ½ inch

mark.

PART 2Now, you will conduct the resistor test with an LED.

Materials you needYour homemade resistor from PART 12 LEDs (I suggest different colors)1 9-volt battery2 connectors (alligator clips or the pinchers type - don’t pick 2 of the same color) PencilYou will not be using the multimeter!

Select one of the connectors and clamp one end to the positive terminal of the 9 volt battery. Clamp the other end to the positive side of the LED.

Page 4 of 9The Positive (+) side of the battery is the male terminal. The Negative (-) side is the

The positive side of the LED is USUALLY the one with the longer leg. The negative side of the LED is the side that has a flat edge. It can be hard to see, so you have to look carefully.

As shown in the video, you may want to loop the LED leads so it doesn’t twirl in the clamp. You may also want to loop the negative side of the LED so it can rest on the “homemade resistor” more easily.

Now, take the 2nd connector and clamp one end to the negative terminal of the battery and lay the other end on the homemade resistor.

Slide the connector along your homemade resistor while the LED wire is resting on the bar. Having the lights off will help you see if the LED is lighting up or not. If the LED does not light, you may have the positive and connections backwards. It must be positive to positive and negative to negative. TRY NOT TO TOUCH THE LED WIRE TO THE connector – IT MAY BURN UP/OUT.

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Record your findings and observations.1) What color resistors (LEDs) did you use?

2) Were the results different? If so, how were they different? Explain in detail.

3) Did you burn up any? If so, explain in detail what happened.

4) Provide comments on this part of the activity. What would you change? What worked? What didn’t work?

5) Before this activity, how well did you understand resistors? How did you learn about them and what was the application.

The Positive (+) side of the battery is the male terminal. The Negative (-) side is the

PART 3Now that you know understand what resistors do, you will practice determining their values.

As shown previously, resistors come in many different shapes and sizes. We are going to concentrate on the type depicted in the image on the upper right. Notice the colored bands. Sometimes the color is duplicated and sometimes not. Each band color in a specific location represents a certain value. By reading and combining all of the bands, we can determine the value of the resistor. Resistors are measured in ohms named after the German physicist Georg Simon Ohm. The symbol that represents ohms is the Greek letter omega ( ).

When resistors are manufactured, they are done so with certain applications in mind. Therefore, the manufacturer makes the resistor to meet specific values. Living in a real world means making a resistor EXACTLY the same value as designed is likely NOT to happen. So the manufacturer/designer allows a variance or tolerance. That means they can go over or under the design value by a certain amount. This variance is given in the form of plus/minus a percent.

Example: A manufacturer is asked to make resistors with a design value of 480kΩ and a variance (or tolerance) of 5%. This means, as shown in the table below, that the lowest value acceptable is 456kΩ and the highest value acceptable is 504kΩ.

Design Value Variance

Acceptable RangeLow High

480kΩ ±5 %whichmeans±0.05 ∙480 kΩ=±24k Ω 480 kΩ−24k Ω

¿456 kΩ480 kΩ+24k Ω

¿504 kΩ

Before reading the bands on resistors, you need to be familiar with numerical prefixes often used. These are shown in the following table. We will only be using a few of these prefixes in this activity.

Using this table of prefixes,

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Table of Common Metric PrefixesMetric Prefix Symbol Power of

10Factor

Tera T 1012 1,000,000,000,000Giga G 109 1,000,000,000

Mega M 106 1,000,000kilo k 103 1,000milli m 10-3 .001

micro μ 10-6 .000001nano n 10-9 .000000001pico p 10-12 .000000000001

This color code chart on the right is what we will be following to “read and interpret” the bands on the resistors. A color copy of this chart will be provided for your use as part of the activity.

Example: Inspect the resistor shown on the right. The bands (from left to right) are orange, white, yellow and silver. The color code table was used to determine the design value of the resistor. This is shown in the table below.

Resistor Number

Color On Bands

Design Value (DV)

Range1st Band 2nd Band 3rd Band

Multiplier4th Band

Tolerance

Low High

Example

Orange White Yellow Silver

Value Of Each Band

3 9 104 ±10% 390,000=390kΩ

390 -0.10*390=351kΩ

390 + 0.10*390=429kΩ

Measured Value From Multimeter(MV) 376KΩ Does the % Error of the

Measured Value Fall Within the Allowed

Tolerance? Yes or No

Yes, because 3.6% is within ±10%

% Error of MV = (DV – MV)/DV(ignore the sign of your answer)* (390-376)/390 = 3.6%

*To get the percent of error, subtract the multimeter value from the design value. Divide that answer by the design value. Ignore the sign of the answer. You will get a decimal. Change that to a percent, then compare it to the +/- tolerance.

Select two different resistors (they should have different sequences of color) and fill in the tables below. You will first determine the value of each resistor based on the colors and then actually measure each resistor on the multimeter. Then compare how the design value compares to the measured. If the resistor you choose has 5 values you can ignore the extra band; we will be working with only 4 bands. Remember, the last band you are reading should be either silver or gold.

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Resistor Number

Color On Bands

Design Value (DV)

Range1st Band 2nd Band 3rd Band

Multiplier4th Band

Tolerance

Low High

1 Value Of Each Band

Measured Value From Multimeter(MV) Does the % Error of the

Measured Value Fall Within the Allowed

Tolerance? Yes or No

% Error of MV = (DV – MV)/DV(ignore the sign of your answer)

Resistor Number

Color On Bands

Design Value (DV)

Range1st Band 2nd Band 3rd Band

Multiplier4th Band

Tolerance

Low High

2 Value Of Each Band

Measured Value From Multimeter(MV) Does the % Error of the

Measured Value Fall Within the Allowed

Tolerance? Yes or No

% Error of MV = (DV – MV)/DV(ignore the sign of your answer)

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COMMENTS ON PART 3 -Give two observations or findings you made about the resistors you calculated and then measured. (EXAMPLE: Were you able to get measurements? Did any of them fall outside the design range? Were the measurements difficult to determine? What settings did you use on the multimeter? Did you have to change the settings when going from one resistor to another? Did you choose the settings and then measure or measure and then adjust the settings? Were the resistors difficult to read? Why? Were the resistors difficult to calculate? Why?

Give two positive comments about this activity.

Give two suggested changes to this activity to make it better.