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Interpreting an XY Scatter Graph. Example Ohm’s Law. Data. If we set up a circuit with some resistor and an ammeter (to measure current) in series. And supply voltages 1,2,3,4, and 5 volts respectively, the currents (in milliAmperes) shown were measured. - PowerPoint PPT Presentation
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Data
If we set up a circuit with some resistor and an ammeter (to measure current) in series. And supply voltages 1,2,3,4, and 5 volts respectively, the currents (in milliAmperes) shown were measured.
Current versus Voltage
• In our set up, we controlled voltage. Furthermore we used the convention that the variable we controlled is plotted on the x-axis.
• Now we want to compare the fit line (Trendline) from Excel with the equation from our theory – Ohm’s Law. Excel: y = 0.2807x + 0.0019Theory V=IR
Units of slope
• Slope is “rise over run” so its units are mA/V. • The resistance was the reciprocal of slope, so
its units are V/mA. • The m means milli means 10-3.• A factor of 10-3 in the denominator
corresponds to a factor of 10+3 in the numerator. 10+3 goes with kilo or k.
• A volt/ampere is an ohm. Thus we have units for the resistance in kilo-ohms.
Interpolation
• Our equation y = 0.2812x or I = 0.2812V allows us to guess what the current would be for voltages that we did not measure.
• For instance, we would expect the current corresponding to a voltage of 2.5 to be 0.2812*2.5 = 0.703 mA.
• When we use the Trendline to estimate a new value within our range (here 1-5 volts), this is called Interpolation.
Extrapolation
• We can also use our results to estimate what the current would be for voltages outside the range we measured.
• For instance, we would expect the current corresponding to a voltage of 6 to be 0.2812*6 = 1.6872 mA.
• When we use the Trendline to estimate a new value outside our range (here 1-5 volts), this is called Extrapolation.