Section 1: Introduction

The remarkable lemon, is used in a range of todays commercial products from soaps and detergents, flu and cold remedies, added fragrances and even a battery that produces a voltage and current for experimentation purposes !!

Section 2: Electrodes Copper & Zinc

Very conveniently, the tangy juice inside the lemon form the electrolyte and two electrodes namely copper and zinc complete the cell. A small piece of galvanized guttering may be used as the zinc electrode (negative -) and a piece of thicker copper wire with the insulating plastic removed from both ends may be used as the copper electrode (positive +). Add a bit of solder to both ends of the copper wire to keep all the smaller strands of copper wire more rigid and from spreading out and bending in all directions. When inserting the electrodes inside the lemon, take care that the electrodes do not touch inside the lemon.

Figure 1: Lemon Cell Electrodes Copper & Zinc

Section 3: Voltage Measurement

Actually one lemon is only one cell. More than one lemon hooked up in series or parallel may be described as a battery. The SI unit of voltage is the volt. Make use of a multimeter set to DC volt, scale, for example to 20V, this mean that the maximum volt to be measured is 20V. Connect the red probe (positive +) of the multimeter to the copper electrode (positive +) of the lemon cell and the black probe (negative -) of the multimeter to the zinc electrode (negative -) of the lemon cell. The reading will most probably be just below one volt, 1V. The measurement may also be in the millivolt range for example DC volt 2000mV. To convert volt to millivolt, multiply the volt value by a 1000, for example 0.96V x 1000 = 960mV. To convert millivolt to volt, divide the millivolt value by a 1000, for example 960mV / 1000 = 0.96V. The digital multimeter may show a minus sign on the liquid crystal display, indicating that the polarity (plus and minus) on the probes has been swapped. The photo below illustrate the voltage reading procedure.

Figure 2: Lemon Cell Voltage Measurement

Section 4: Current Measurement

The current that the lemon cell produces may also be measured. Please note that on some multimeters one of the probes may need to be physically plugged out of the multimeter and plugged into an adjacent socket, for the multimeter to be able to measure ampere. The SI unit of current is the ampere. Make use of a multimeter set to direct current DC ampere, scale, for example to 200uA, this mean that the maximum ampere to be measured is 200uA. Connect the red probe (positive +) of the multimeter to the copper electrode (positive +) of the lemon cell and the black probe (negative -) of the multimeter to the zinc electrode (negative -) of the lemon cell. The reading will most probably be just below two hundred microampere, 200uA. The measurement may also be in the milliampere range for example direct current DC ampere 20mA. To convert milliampere to microampere, multiply the milliampere value by a 1000, for example 0.19mA x 1000 = 190uA. To convert microampere to milliampere divide the microampere value by a 1000, for example 194.1uA / 1000 = 0.194mA. The digital multimeter may show a minus sign on the liquid crystal display, indicating that the polarity (plus and minus) on the probes has been swapped. Note that the current reading decreases steadily. The photo below illustrate the current reading procedure.

Figure 3: Lemon Cell Current Measurement

Section 5: Lemon Cells in Series

Now we have a lemon battery ! All the lemon cells are connected in series, thus, behave according to the rules of a series circuit. The copper electrode (positive +) of one lemon cell connect to the zinc electrode (negative -) of the next lemon cell and so on, until all the lemon cells are connected together to form a lemon battery. In a series circuit the current everywhere in the circuit is the same. With seven lemons the total current reading on the digital multimeter is 120uA or 0.12mA and the total voltage reading on the digital multimeter was 6.49V or 6490mV. In a series circuit the voltage over each component may be added together to calculate the total voltage of the series circuit. Previously, the measured voltage over one lemon cell is 0.96V. The formula will then be the measured voltage over each lemon cell, times the quantity of lemons connected in series in the circuit. That is 0.96V x 7 = 6.72V, which is close to the measured voltage of 6.49V. The electrical power of the lemon battery does decrease over a period of time. Note, in a series circuit the total voltage measured is equal to the voltage measured over one lemon cell, times the quantity of lemon cells connected in the series circuit and the total current measured is equal to the current measured through one lemon cell.

Figure 4: Lemon Cells in Series Voltage & Current

Figure 5: Lemon Cells in Series Voltage	Figure 6: Lemon Cells in Series Current

Section 6: Lemon Battery Lighting a LED

In a practical experiment, with seven lemon cells connected in series a red 10mm hyper bright light emitting diode was able to light up. The lemon battery provided sufficient forward voltage and sufficient forward current for the light emitting diode to conduct and emit light. The forward voltage of the light emitting diode is less then 2V. Experimenting further the light emitting diode lit up even with only two lemon cells connected in series producing a measured voltage of 1.90V. Amazing, with only two fruit there is light ! For the light emitting diode to conduct and emit light, the anode of the light emitting diode need to connect to the copper electrode (positive +) side of the lemon battery and the cathode of the light emitting diode need to connect to the zinc electrode (negative -) side of the lemon battery.

The following results were obtained with the two lemon cells in series and one light emitting diode. The light emitting diode was lit for a total of nineteen days. On the tenth day one of the lemon cells did not provide any electrical power and was replaced by another lemon cell that was picked from a lemon tree on the same day as all the other lemons. The other lemon cell was not replaced and continued to provide electrical power for the time period of nineteen days. It is important to note that the zinc electrodes (negative -) was replaced a number of times during the time period of nineteen days, demonstrating one of the properties of a primary cell.

Figure 7: Lemon Battery Lighting a LED

Section 7: Lemon Cells in Parallel

Again, we have a lemon battery ! All the lemon cells are connected in parallel, thus, behave according to the rules of a parallel circuit. The copper electrode (positive +) of one lemon cell connect to the copper electrode (positive +) of the next lemon cell and the zinc electrode (negative -) of one lemon cell connect to the zinc electrode (negative -) of the next lemon cell, until all the lemon cells are connected together to form a lemon battery. In a parallel circuit the voltage everywhere in the circuit is the same. With seven lemons the total voltage reading on the digital multimeter is 0.96V or 960mV and the total current reading on the digital multimeter is 973uA or 0.973mA. In a parallel circuit the current through each component may be added together to calculate the total current of the parallel circuit. Previously, the measured current through one lemon cell is 120uA. The formula will then be the measured current through each lemon cell, times the quantity of lemons connected in parallel in the circuit. That is 120uA x 7 = 840uA, which is in proximity of the measured current of 973uA. The current produced by the individual lemon cells differ from each other, producing more an average total current, but, in electrical and electronic engineering the calculations are basically exact. The electrodes and electrolyte inside the lemon need to make good contact, especially as the lemon ages over a time period of hours or days. The electrical power of the lemon battery does decrease over a period of time. Note, in a parallel circuit the total voltage measured is equal to the voltage measured over one lemon cell and the total current measured is equal to the current measured through one lemon cell, times the quantity of lemon cells connected in the parallel circuit.

Figure 8: Lemon Cells in Parallel Voltage	Figure 9: Lemon Cells in Parallel Current

Section 8: Lemon Battery Not Lighting a LED

With seven lemon cells connected in parallel, a red 10mm hyper bright light emitting diode was unable to light up. The lemon cells in parallel, forming a lemon battery, provided only 0.96V to the light emitting diode and are not sufficient for the light emitting diode to conduct and emit light. The forward voltage of the light emitting diode is less then 2V and only 0.96V is available.

Figure 10: Lemon Battery Not Lighting a LED

The last time this page was modified, was: 5:55 pm, 26 Apr 2010

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