Finding the Internal Resistance of a lemon when used as a Power Supply?

Hi There,



Right I recently did an experiment in Physics to find out the internal resistance of a lemon when used as a power supply.



We connected the lemon to a voltmeter, ammeter and variable resistor, changed the resistance on the variable resistance and measured the voltage and current against each other.



So i have a table of voltage against current.



I have drawn a graph of voltage against current, voltage on y axis, and current on the x axis. And drawn a line of best fit. Voltage is in milli volts, 10^-3 and current is in micro volts 10^-6



How would i go about finding the EMF and eventually the Internal resistance of the lemon when used as a power supply.



Also how would i go about finding the intercept of the graph if the line of best fit does not go through the y axis on the scale i have used.



Anything to help would be fantastic



Thank you in advance.Finding the Internal Resistance of a lemon when used as a Power Supply?
The lemon's internal resistance will be the (negative of the) slope of line of best fit and your EMF will be the point at which the current = 0, i.e., your y intercept. To find the slope of your line, pick two convenient points on it, for best precision as far apart on the line as possible. The slope will be the difference in voltage divided by the difference in current.



To find the EMF, the procedure will be much the same as you used in algebra to convert a linear equation from point-slope form to slope-intercept form. You now have your slope. If (Io, Vo) is one of the points on your line, you can now construct an equation of the form



V - Vo = m(I - Io) The y intercept will be the value of y (alias V) when x (alias I) becomes zero. Substitute zero for I and solve for V. The result will be your EMF.Finding the Internal Resistance of a lemon when used as a Power Supply?
Internal resistances of lemon, potatoes etc increase with increase in current in a highly nonlinear manner. The internal resistance and its variation depend on the origin of these lemons and potatoes. Canadian lemons and French lemons do not show much of a similarity in their behaviour as well as in their useful duration.

And the results are not reproducible. This is not a discouraging note but only points out that there are many unknown elements in this field.