CURRENT VOLTAGE EXPERIMENT 5 DC I CHARACTERISTIC OF OHMIC AND NON OHMIC DEVICES Object To determine the current voltage characteristic curve of a resistor and silicon diode and to determine the resistance of the resistor Prior to lab A particular measurement of current and potential difference can be used to determine a characteristic resistance for an electrical element operating under specific conditions For example a current of 0 250 A through a resistor when a potential difference of 0 815 V is applied yields according to Ohm s Law a specific resistance for those operating conditions Predict the resistance and its measurement uncertainty for the specific current and potential difference stated in the above example Assume the measurement uncertainty is that given for the DMM s used in lab Discussion 1 Definition of terms DC or direct current is a current that is constant in magnitude and direction Voltage is used as another term for electric potential difference I V characteristic curve or current voltage characteristic curve is a graph of the relation between the current through a device and the potential difference across the terminals of the device Resistance is the result of moving charges current colliding with atomic cores in a conductor when a voltage is applied It is defined in terms of Ohm s Law as R A device is considered ohmic if the ratio of voltage to current is constant Polarity is a way of showing the relative magnitude of voltage or the direction of current In terms of voltage the higher value of voltage is relatively more positive and should be connected to the plus terminal of a voltmeter Conventional current is taken as the direction of motion of positive charges The current flows from higher electric potential to lower electric potential refers to the polarity of the connections to a circuit element resistor diode etc Determine how bias may be used to describe the behavior of the circuit elements used in this experiment Bias 1 14 2019 1 Figure 1 The wire wound resistor used in the experiment The value of this resistor is 10 The maximum current capacity of the resistor is 0 45 amp Figure 2 The diode used in the experiment The maximum current capacity of the diode is 1 0 amp Power Supply with Switch A Resistor V Figure 3 A representative arrangement of the apparatus The diode will replace the resistor for the second part of the experiment Figure 4 A wiring schematic for the apparatus shown at the left PROCEDURE 1 Wire the circuit as shown Connect the resistor in the position labeled sample DO NOT PLUG IN POWER SUPPLY OR SWITCH IT ON Do ask your instructor to check your circuit for correctness of wiring Your instructor will adjust the output of the power supply to a maximum of 1 95 volts and set the current limit for 190 mA DO NOT CHANGE THE CURRENT SETTINGS 2 Measure the voltage and current pairs of the resistor for 10 different values Reverse the connections to the resistor and make another 5 measurements Label this second set of readings as negative or reverse bias DO NOT EXCEED 190 mA ON THE AMMETER 1 14 2019 2 3 Remove the resistor and connect the diode Repeat the above instructions HINT In the forward bias orientation of the diode the current changes very rapidly choose very small changes in the voltage DO NOT EXCEED 190 mA ON THE AMMETER ANALYSIS 1 Create a table for your measured values of I and V for the resistor and another table for the diode 2 For the resistor only calculate the resistance for each I V pair you measured Using the definitions in the write up on error determine the mean average resistance and standard deviation for your measurements Use the spreadsheet to quickly do all these calculations Ask your instructor for assistance if necessary 3 For the resistor only graph the V vs I characteristic curve and determine the best average value of R by using a trend line determination with I as the independent variable x axis and V as the dependent variable y axis Does the trend line have a y intercept equal to zero Include the results of the trend line as a graphed line on your V I plot Also be sure the equation of the trend line is shown on the graph 4 For the resistor only determine the maximum instrumental error uncertainty for your set of measurements Report this uncertainty with the value of R determined from the trend line NOTE The calibration and reading error for the DMM on DC amps is 2 of the reading 1 digit 5 For the diode graph the I vs V characteristic curve Plot the V on the x axis REPORT Your report should include a discussion on the nature of the characteristic I V curves for the diode and resistor Compare your value of R from the trend line with the mean value of the set of calculated values of R and with the manufacturer s claimed value Be sure to include the relevant uncertainties with each value of R you report What do you conclude about the nature of your measurements Report any sources of error in the experiment 1 14 2019 3