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| [https://wiki.iac.isu.edu/index.php/Electronics_Lab_Reports_RS Go Back to All Lab Reports]
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| =Kirchoff's Law (50 pnts)=
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| == Smokey Circuits==
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| When doing these labs it is important to determine the limitations of your electrical components in order to avoid damaging them.
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| This lab uses resistors. Resistors are vulnerable to melting if you push too much current through them.
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| Resistors have power ratings ranging from 1/8 Watt up to several Watts. The common resistors are rated at 1/4 Watt. Let's assume this rating for the resistors in this lab.
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| Determine the maximum voltage of the DC power supply you will use. (ie, 30 Volts)
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| ;<math> P =I^2R = V^2/R \Rightarrow R = \frac{V^2}{P} > \frac{\left (30 V \right)^2}{1/4 \mbox{Watt}} > 3600 \Omega</math>
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| :By keeping your resistance values above 3600 <math>\Omega</math> you should be able to avoid burning up 1/4 Watt resistors when your max voltage is 30 Volts.
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| The next objective is to use resistors which allow currents that you can measure with your voltmeter.
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| ;Since <math>V=IR \Rightarrow I = V/R = 30 \mbox{Volts}/3600 \Omega = 8\mbox{mA}</math>
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| Determine the range of currents which the voltmeter can measure. (ie 1 mA)
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| To get measurable currents you need low resistance BUT the lower resistances will need to have a high power rating. These two competing properties limit the range of resistances you can use.
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| Select the three resistors you should use for this experiment.
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| ==Construct the circuit below==
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| [[File:TF_EIM_Lab1.png | 400 px]]
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| ==Enter the values of the DC voltage and Resisters that you used.==
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| Use a voltmeter to measure the potential difference and resistances.
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| {| border="3" cellpadding="20" cellspacing="0"
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| |Variable ||Measured Value
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| | <math>V_A </math> || 1.570 V
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| | <math>R_1</math> || 99.4 <math>\Omega</math>
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| | <math>R_2</math> || 990 <math>\Omega</math>
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| | <math>R_3</math> || 9.79 <math>k\Omega</math>
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| |}
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| ==Enter the measured and predicted quantities in the table below==
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| Given <math>V_A</math> and the values of all resistors, use Kirchoff's laws to predict
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| a.) Predict the value of <math>V_B</math>
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| b.) Predict the values of the three currents.
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| c.) compare your predictions and measurements by filling in the table below.
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| {| border="3" cellpadding="20" cellspacing="0"
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| |Variable ||Measured Value|| Predicted Value|| % Difference
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| | <math>V_B</math> || || ||
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| | <math>I_1</math> || || ||
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| | <math>I_2</math> || || ||
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| | <math>I_3</math> || || ||
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| |}
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| = Internal resistance (30 pnts)=
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| Measure the internal resistance of a "D" cell battery by graphing the current on the x-axis and the measured voltage on the y-axis for several values of the resistance <math>R_L</math> shown in the circuit below. Begin with <math>R_L = 1k\Omega</math> and then decrease it by a factor of 5 for each subsequent measurement. You can use a volt meter to measure the current and potential difference.
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| [[File:TF_EIM_Lab1a_fig.png | 200px]]
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| {| border="3" cellpadding="20" cellspacing="0"
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| | R_{Load} (<math>\Omega</math>) || V (Volts)|| I (mA)
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| | 0.5|| ||
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| | 10|| ||
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| | 47|| ||
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| | 93|| ||
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| |990 || ||
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| |}
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| =Questions (20 pnts)=
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| #What conservation law is involved in Kirchoff's Loop Theorem?
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| #What does the slope in the internal resistance plot above represent?
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| [[Forest_Electronic_Instrumentation_and_Measurement]]
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| [https://wiki.iac.isu.edu/index.php/Electronics_Lab_Reports_RS Go Back to All Lab Reports]
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