UMass Amherst PHYSICS 132 - COMPL Phys 132 Lab 5 - DC Circuits (11 pages)

Physics 132 Lab Lab 5 DC Circuits Experimental Design and Modeling Connect the red wire from the PASCO 550 power supply to the red post of the 100 ohm resistor Connect the black wire from the PASCO 550 power supply to the black post of the 100 ohm resistor now you have a circuit The power supply measures the amount of current through the circuit Connect the red and black wires from channel A of the PASCO 550 to the red and black posts of the 100 ohm resistor respectively Channel A will measure the voltage applied across the resistor Use the PASCO Capstone software to measure the voltage and current for the resistor 1 Record about 10 measurements of voltage and current for the the resistor Your measurements should range from 5V to 5V Record measurements in spreadsheet provided Resistor 1 Current A Voltage V 0 05168 4 975 0 04133 3 979 0 03097 2 984 0 02064 1 989 0 01028 0 993 0 01042 0 997 0 02077 1 991 0 03111 2 986 0 04146 3 982 0 05182 4 976 Now that you have taken a set of measurements of voltage and current for the resistor let s try to figure something about the resistor Is there a pattern between the voltage across and current through a resistor How can we understand what the pattern is The pattern is that as voltage increases so does the current This means the two have a direct relationship We can understand what the pattern is by graphing the values we recorded and seeing their relationship 2 Make a graph of voltage vs current for the resistor Make sure the voltage is plotted on the y axis vertical and current is plotted on the x axis horizontal 3 Describe the relationship between voltage and current for the resistor Explain a mathematical model for the relationship What are the parameters in the model you would use and how do the parameters relate to properties of the resistor For the resistor there is a positive linear relationship between the current and voltage This means that as the current increases the voltage also increases The parameters are slope 96 1 and y intercept 0 00534 In relationship to the resistor the slope is equivalent to the resistance of the resistor in ohms The y intercept would be equal to the voltage when current is equal to zero Now connect the red and black wires from channel A to the red and black post of the second resistor 4 Record about 10 measurements of voltage and current for the second resistor Your measurements should range from 5V to 5V Record measurements in spreadsheet provided Resistor 2 Current A Voltage V 0 05159 4 975 0 04128 3 979 0 03093 2 984 0 02062 1 989 0 01027 0 993 0 01042 0 996 0 02076 1 991 0 03107 2 986 0 04141 3 982 0 05175 4 976 5 Make a graph of voltage vs current for the second resistor Make sure the voltage is plotted on the y axis vertical and current is plotted on the x axis horizontal 6 Describe the relationship between voltage and current for the second resistor Explain a mathematical model for the relationship What are the parameters in the model you would use and how do the parameters relate to properties of the second resistors There is a positive linear relationship between the current and the voltage for the second resistor so as the voltage increases so does the current The mathematical relationship between voltage and current can be seen in the formula V RI where V voltage R proportionality constant and I current In the model we used the parameters are slope 96 3 and y intercept 0 00583 The slope is equivalent to the resistance of the resistor measured in ohms the y intercept is equivalent to the voltage when the current is 0 Series and Parallel Circuits One device in a circuit is not very interesting or useful Let s consider what happens when more than on device is connected in a circuit Devices can be connected two ways in series and in parallel First connect the two 100 ohm resistors in series shown below The red wire from the power supply is connected to the red post of the first resistor The black wire from the power supply is connected to the black post of the second resistor Connect a red wire from the black post of the first resistor to the red post of the second resistor You now have a series circuit The red wire between the two resistors means there is only one path between the resistors that current can flow That means the current through one resistor will always be the same as the current through the other Let s see what happens as we varies the voltage across the series circuit Connect the red wire from channel A to the red post of the first resistor and connect the black wire from channel A to the black post of the second resistor 7 Record about 10 measurements of voltage and current for the two series resistors Your measurements should range from 5V to 5V Record measurements in spreadsheet provided Series Circuit Resistor 1 and 2 Current A Voltage V 0 02599 4 978 0 02081 3 982 0 01559 2 986 0 01037 1 99 0 00516 0 994 0 00524 0 997 0 01048 1 993 0 01566 2 988 0 02089 3 985 0 02612 4 98 8 Make a graph of voltage vs current for the two series resistors Make sure the voltage is plotted on the y axis vertical and current is plotted on the x axis horizontal 9 Describe the relationship between voltage and current for the two series resistors Explain a mathematical model for the relationship What are the parameters in the model you would use and how do the parameters relate to properties of the two resistors This two series resistor model shows a positive correlation between current and voltage This mathematical relationship can be explained by the formula V RI where V voltage R proportionality constant and I current In the model we used the parameters are slope 191 and y intercept 0 00768 The slope is equivalent to the resistance of the resistor measured in ohms the y intercept is equivalent to the voltage when the current is 0 Another way to connect two resistors is in parallel This is easily done by connect a wire to the two red posts of the resistors and connecting a second wire to the two black posts of the resistors There are now more than one path that current can flow between the two resistors Let s measure the voltage and current for the parallel circuit Connect the red wire from channel A to the red post of the first resistor and connect the black wire from channel A to the black post of the second resistor 10 Record about 10 measurements of voltage and current for the two parallel resistors Your measurements should range from 5V to 5V …