PHY 202 - Laboratory LABORATORY 6: RESISTORS resistance = 0.67 ohm R = PL P L A Objectives: Explain the difference between resistance and resistivity. A Predict how geometry and resistivity affect the resistance of a 0.50 0 7.50 resistor. Verify Ohm's Law. Resistance in a Wire PhET. : Materials Required: Computer Computer with Excel and access to Resistance in a Wire and Battery Resistor Circuit simulations: https://phet.colorado.edu/sims/html/resistance-in-a- wire/latest/resistance-in-a-wire_en.html http://phet.colorado.edu/en/simulation/battery-resistor-circuit Software Requirements: Windows Macintosh Linux Microsoft Windows XP/Vista/7/8.1/10, OS X 10.9.5 or later, latest version Latest version of Java latest version of Java of Java Introduction: The resistor is an electrical component to create resistance in the flow of electric current. Resistors are found in almost all electrical networks and electronic circuits. If the resistance is constant over a considerable range of voltage, the behavior of the resistor is dictated by the relationship specified by Ohm's law: V = IR Ohm's law states that the voltage (V) across a resistor is proportional to the current (1), where the constant of proportionality is the resistance (R). The ohm (symbol: 2) is the SI unit of electrical resistance. An ohm is equivalent to a volt per ampere. Length. (2) The electrical resistance of a wire is greater for a longer | Area (4) wire, less for a wire of larger cross-sectional area, and Resistance equals: R depends upon the material out of which the wire is made. Experimentally, the dependence upon these properties is expressed as:The factor in the resistance which takesuintguaccgunt the nature of the material is the resistivity, and it is it is temperature dependent. The electrical resistivity p of a particular conductor material is a measure of how strongly the material opposes the ow of electric current through it. Over sizable ranges of temperature. its temperature dependence can be predicted from a temperature coefcient of resistance. Activity 1: Resistance of a Wire 1. Start the Resistance in a Wire The; simulation and explore it. You will verify the equation I , . . R p Z usmg the m Simulation. Increase the resistivity p of the resistor While keeping L and A constant, to investigate how the resistance of the resistor changes. Record your data in Table 1 below. L : A : Table l: ( 111) () Use Excel to plot a graph of R 173. p (see LUOiExcel le for help). Make sure that your graph is a scatter plot. Customize the graph graph title and label the axes (using the Chart Tools menu). Add the bestt line passing through your data points (use the T rendline 111611th Check the Display Equation on Chart option near the bottom. Insert a copy (screenshot) of your graph in the space below. 4. Does a linear t describe your data? Compare the slope of the graph to the ratio i. 5. Increase the length of the resistor While keeping the resistivity p and A constant. Record your data in Table 2 below. Table 2: (m) (0) 6. Use Excel to plot a graph of R 115.1,. Add the bestt line passing through your data points (use the T rendline menuLand check the Display Equation on Chart option near the bottom. Insert a copy (screenshot) of your graph in the space below. 7. Does a linear t describe your data? Compare the slope of the graph to the ratio 2- 8. Increase the area of the reststor while keeping the reststivrty p and L constant. Record w data in Table 3 below. Table 3: (In) (m'l) () 9. 10. 11. 12. Use Excel to plot a graph of R vs. A\". Add the best-fit line passing through your data points (use the Tremine 1116131le check the Display Equation on Chart option near the bottom. Insert a copy (screenshot) of your graph in the space below. Does a linear fit describe your data? Compare the slope of the graph to the product pL. Does your data prove that R : pi 7 Based on your data, what must happen for the Wire's resistance to be at its greatest? Activity 2: Ohm's Law 13. 14. 15. 16. 17. 18. 19. Start the Battery Resistor Cincian simulation and explore it. Make sure that the Show core box is checked. The simulation allows you to change either the potential difference (voltage) of this circuit or the resistance. Play around with these variables to see what happens when you increase and decrease each one. How does increasing the resistance affect the current passing through the circuit? What must happen to the voltage and resistance for the circuit to get hot? What happens to the current in this scenario? What must happen to the voltage and resistance for the circuit to get cold? What happens to the current in this scenario? Set the voltage to 7.20 V and do not change it, For the resistance values listed in Table 4 below, read the current in the circuit on the arruneter dial in the lower left-hand corner. 11 Table 4: R (m (A) [1 (A71) .20 .40 .60 .80 .93 30. Use Excel to plot a graph of R 173.1\". Add the best-t hue passing through your data points (use the Trendline menuLand check the Display Equation on Chart Option hear the bottom. Insert a copy (screenshot) of your graph in he space below. 21. Does a linear fit describe your data? Compare the slope of the graph to the voltage recorded above, by calculating the diff. %diff : slope 7 recorded voltage x 100 recorded voltage 22. Set the resistance in this circuit to 0.60 (2 and do not change it. Start at 9.0 V and incrementally decrease the voltage for the 6 trials ammeter dial in the Table 5: ower left-hand isted in Table 5 below. Read the current in the circuit on the corner. V 1 (V) (A) 9.0 23. Use Excel to plot a graph of V v5.1. Add the bestt line passing through your data M check the Display Equation on Chart option near the bottom. Insert a copy (screenshot) of your graph in the space below. 24. Does a linear fit describe your data? Compare the slope of the graph to the resistance recorded above, by calculating the % diff. % diff [slope - recorded resistance x 100 recorded resistance 25. Does your data verify Ohm's Law V = I R? References: CC-BY license, PhEI Interactive Simulations, University of Colorado Boulder, http://phet.colorado.edu https://phet.colorado.edu/sims/html/resistance-in-a-wire/latest/resistance-in-a-wire en.html http://phet.colorado.edu/en/simulation/battery-resistor-circuit 6