UlC Physics Department Physics 142 Laboratory Manual Part 2: Resistivity Voltage vs Length From Eq. (2) it follows that if the cross-sectional area of a wire is constant, then the wire's resistance R changes linearly with its length. Let's use the wire #1 to verify how resistance does vary with its length. To do that, Table 3 2.1. Check that Voltage Sensor's black plug is inserted to wire's black #1 connector. 2.2. Click \"Record" button in "Control\" menu and gently adjust the output voltage until the power supply's voltmeter shows 3.0 V. 2.3. Slide the Voltage Sensor's red plug along wire #1 and record the Voltage readings at the positions listed in Table 3. 2.4. Connect Voltage Sensor's red plug to wire's red #1 connector and record Current reading below. 1=(A) Then, click "Stop" button. Calculate W] for each L and record its values in Table 3. 2.5. Plot Rvs L graph (in LibreOffice Calc). Use LINESTQ function to find the slope, intercept and its uncertainties. Record its values and the coefficient of determination, R2, below. Wire #1: slope#1 = i Q/m Interceptjj1 = i Q R2 = Voltage vs Cross-sectional Area From Eq. (2) it also follows that if the length of a wire is constant, then resistance R is inversely proportional to its cross-sectional area A. Table 4 2.6. You already found the cross- sectional areas of the wires #1, #2 and #3, so just copy its values from Table 1 to Table 4. We can increase the number of data points by combining these three wires with each other. For instance, the wire "1 8; 2\" listed in Table 4 (the third row in the first column) means that the wires #1 and #2 are connected in parallel. Therefore, this "wire" has area A = A\" + A\" and it can be "made" by using jumper cables connecting #1 black plug with #2 black plug and #1 red plug with #2 red plug, respectively. Resistance and Resistivity Page 4- ot'6 UlC Physics Department Physics 142 Laboratory Manual 2.7. Calculate the cross-sectional areas of the rest of the wire combinations and record their values in Table 4. 2.8. Check that the power supply's voltmeter shows 3.0 V. If not, gently adjust Voltage (either coarse or ne) knob to get 3.0 V, then click "Record" button. 2.9. Record the Voltage sensor and Current sensor readings for each of wires and its combinations in Table 4. 2.10. When done, turn both Voltage knobs all the way counterclockwise (Voltage sensor reading should be 0.0 V). click \"Stop\" button to stop running Capstone. close the program and turn Power Supply OFF. 2.11. Plot R/L vs 1/A graph (in LibreOffice Calc). Use LINESTO function to find the slope (p), intercept and its uncertainties. Record these values and the coefficient of determination, R2, below. p = i Q - mmZ/m Intercept = i Q/m R2 = 2.12. Use Table 5 to identify from which material the potentiometer's wires are made Use Table bl 5 Ta e Wire s material . Resistivity Material 2 2.13. Does the wire's resistance you have measured 9 ' mm m obey Ohm's law? In answering this question, consider Constantan CuNi allo the graph and best fit you have made in the first part Kanthal A-l (FeCrAl alloy) 1.4 of the lab. Remember that linear behavior of Vvs I is Nichrome 60 NiCr allo 1.1 the proof of ohmic behavior. Stainless Steel 316L Tun_sten 0.056 2.14. Do your results in the second part of the lab support that the resistance of a conducting wire is proportional to its length and inversely proportional to the cross-sectional area of the wire? Explain your reasoning. 2.15. What is the precision of your measurements of the resistivity of the materials the wires are made from? Determine the aCCuracy of your measurements of the resistivity. Resistance and Resistivity Page 5 of6