Question

The voltage drop (V) across a resister is proportional to the current (I) through the resister. Ohm's Law: V = IR. Wednesday's laboratory expernnent attempts to verify Ohm's Law and measure the resistance (R) of a resister Ammeters and voltmeters potentially have offsets, resulting in a constant added to the equation: V = IR + VO If voltage satisfying this equation is plotted against current, the result is a line. With voltage on the y-axis and current on the r-axis, the slope is the resistance. Follow this procedure when plotting a line and obtaining a slope 1. Plot the data points 2. With a straight-edge, draw a line following the points. Measurement errors mearn that the actual points scatter. The points wll be above and below the line, with an occasional point intersecting it 3. Finally, measure the slope of the line These are some of the common errors: Connecting the dots. This is a useless exercise. Forcing the line through the origin. The origin should be ignored. One may choose to take a zero-current measurement; that should be treated as a data point reasonable slope The effect of the inherent uncertainty in reading the points is thereby minimized Using the data points for the slope. However, using the endpoints usually gives a . Using points close together on the lne for the slope. Points should be picked far apart Absent among the list off errors above is plotting I on the y-axis, and V on the r-axis. If this happens, hopefully the student can figure how the connection between the slope and the resistance is revised. If units are followed, they indicate the alteration.) A table of voltage-current entries begins on the next page. Use them to estimate the resistance Voltage (Volts)(mA) Current 7.3 8.1 9.6 10.4 13.2 16.9 90.2 101.3 115.6 136.2 170.2 223.3 Graph paper is provided on the third page. Cross out the numbers on the axes and provide your own. Specify the units, of course 1. Plot the data, draw the line, and measure its slope, giving us the resistance. 2. What would the measurement be if you used the two endpoints? 3. What would the measurement be if you used the third and fourth points? . If you wish, you may use a computer to fit a line to the data. It would produce an uncertainty to the fit as well

Answer 1

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