2. Often the goal of an experiment is to find the relationship between two variables. As one variable changes, so does the other. Graphing is a useful way to visualize and describe these relationships. Because the use of graphs is so common in the sciences, it is important that you know how to construct and interpret graphs.

3. 1. Determine which variable is the independent variable (selected values) and which variable is the dependent variable (measured values). Independent variable - voltage Dependent variable - current

4. 2.Always give your graph a relevant title: The relationship between (dependent variable) and (independent variable). The Relationship between Current and Voltage (Potential Difference)

5. The Relationship between Current and Voltage

6. 3.The x-axis of a graph is your independent variable and the y-axis is the dependent variable (unless your teacher tells you otherwise). In this case, your teacher tells you to:  make the x-axis the dependent variable – current  make the y-axis the independent variable – voltage (potential difference)

7. The Relationship between Current and Voltage Current V o l t a g e

8. 4.Determine the limits (maximum and minimum values) for each axis and divide each axis into equal intervals. The axes should be scaled so that the graph takes up as much of the paper as possible. Make sure your graph is as large as possible in the space you've been given. Voltage Resistance Current 5 V10 Ω 0.50 A 10 V10 Ω 1.00 A 15 V10 Ω 1.50 A 20 V10 Ω 2.00 A 25 V10 Ω 2.50 A 30 V10 Ω 3.00 A 35 V10 Ω 3.50 A 40 V10 Ω 4.00 A 45 V10 Ω 4.50 A 50 V10 Ω 4.99 A y-axisx-axis

9. The Relationship between Current and Voltage Current Voltage 10 0 20 30 40 50 12345

10. 5.Always label the x and y axes (a label on the axis describes what those numbers are). Include units if the variable has units (ie. m, cm, s, m/s).

11. The Relationship between Current and Voltage Current Voltage 10 0 20 30 40 50 12345 (A) (V)

12. 6. All data points should be plotted with a dot. To make these dots more visible, place a circle around the dot. Your points should look like this; 

13. The Relationship between Current and Voltage Current Voltage 10 0 20 30 40 50 12345 (A) (V)          

14. 7. Never connect the dots on your graph! When you do an experiment, there are always errors that you can’t control. As a result, experimental data never makes a nice straight line. Instead, it makes a bunch of dots which kind of wiggle around a graph. This is normal.

15. 8.Make a line (or curve) which seems to follow the data as well as possible (line of best fit), without actually connecting the dots. The line should pass as close as possible to each of the points but should not be connected point-to-point. Doing this shows the trend that the data suggests. If the data points seem to show a linear (straight line) pattern, draw a straight line (with a ruler) that passes through the points. If the data points seem to show a curved pattern, draw a smooth curve that passes through the points.

16. The Relationship between Current and Voltage Current Voltage 10 0 20 30 40 50 12345 (A) (V)          

17. 9. If your graph is a straight line, you may determine the slope of the graph. a)Select two distant points on the line. b)Determine the rise (change in voltage). c)Determine the run (change in current). d)slope = rise/run

18. The Relationship between Current and Voltage Current Voltage 10 0 20 30 40 50 12345 (A) (V)           rise run = change in voltage = 40 V – 10 V = 30 V = change in current = 4 A – 1 A = 3 A

19. slope = rise run slope = change in voltage change in current slope = 30 V 3 A slope = 10 V/A How does the slope of this graph compare to the resistance of the resistor used in this activity?

20. Therefore, resistance = voltage current R = V I Ohm’s Law

21. With conductors and some types of loads, the current, voltage, and resistance are related. If the voltage across one of these loads increases, the current through the load also increases. The graph of voltage vs current looks like a straight line. The slope of the graph is the resistance of the load. This straight-line relationship is written as

22. Ex 1) A load has 1.2 A of current flowing through it. The voltage across the load is 6.0 V. Calculate the resistance of the load.

23. Ex 2) A 110 Ω resistor is connected to a power supply set at 12 V. Calculate the current going through the resistor.