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1.2

Minor Versionm

by Procheta Mallik

Introduction

The Voltaic cell was one of the first batteries to be invented and the principle behind its operation is still used in some modern batteries. A simple 'wet' cell consists of two metal plates separated by a liquid, known as the electrolyte. This liquid serves as a channel for balancing the charge between the electrodes when the cell is being discharged.

Video Overview

    • Scissors have functional sharp edges. Contact may result in injury. Always keep blades away from fingers and body. Handle with care.

    • Magnesium is an active metal, people with sensitive skin should avoid direct skin contact.

    • Metal foil or tape can have sharp edges, handle with care.

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  1. You have two 10 cm strips of  polished magnesium. These will serve as the negative terminals of the finished cells.
    • You have two 10 cm strips of polished magnesium. These will serve as the negative terminals of the finished cells.

    • The two 10 cm lengths of copper ribbon will be the positive terminals of our complete cells.

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    • Take one filter paper and fold it in half .

    • Cut about 0.5-1 cm off the folded circumference.

    • Now unfold the paper and cut along the fold line. These two pieces will form the separators for our cells.

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    • Now place one of the magnesium strips on one of the longer sides of the paper separator.

    • Take care that there is at least 1.5 cm of the strip sticking out from the rectangle; this will serve as a negative contact point later. Also make sure that the separator extends a little beyond the other end of the strip.

    • Roll the strip tightly along the rectangular piece to make a cylindrical shape.

    • Hold the bottom of the cylinder to keep it from unravelling.

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    • Now place the magnesium strip wrapped in the filter paper on top of a copper strip. Make sure there is some space between the copper and magnesium electrode.

    • Now fold the copper ribbon strip around the paper to make a mostly sealed envelope of copper around the magnesium electrode separated by paper.

    • The cell is now almost complete and ready to accept the electrolyte.

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    • Make another identical cell, based on the steps mentioned previously, with the remaining materials

    • Attach the positive (copper) of one cell to the negative (magnesium) terminal of the other. Leaving you with one pair of free terminals to connect the LED to. These will be the positive and negative of the battery.

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    • Now wind the positive of the battery to the positive of the LED (longer leg) and the negative of the battery to the negative of the LED (shorter leg).

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    • Start by taking about 10-20 ml of water in a cup.

    • Add the citric acid crystals to the water and stir till they dissolve. This solution will act as our electrolyte.

    • Our average cell voltage with this cell chemistry is 1.2 - 1.5 volts so we need at least two in series to deliver 2.4 volts, which is comfortably above our red LED's switch-on voltage (2.1 volts). If the LED is blue or white instead of red or green, it may need more cells connected in series as these have a higher turning-on potential.

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    • Now dip the the cells inside the electrolyte.

    • The LED should start glowing almost instantaneously!

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    • If the LED does not glow, it could be caused by either an improper connection between the cells or a short (positive and negative of the same cell are touching) on one of the cells.

    • Erroneously connecting the positive (long) lead of the LED to the magnesium electrode and the negative lead to the copper electrode.

    • Insufficient absorption of the electrolyte by separator.

    • Winding the lead of the LED to copper and magnesium could be a little tricky and not robust enough.

    • Electrolyte not concentrated enough, although typically, a dilute solution is adequate.

    • If the cells start hissing and bubbling in the electrolyte, it is too acidic, try diluting it with water for better results.

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    • How many batteries do you need to connect in series to make a red, blue, green and white LED glow? Are they different?

    • What will happen if only one cell with citric acid as the electrolyte is used? Will the LED glow?

    • What if we replace the magnesium with zinc? Will it give the same result?

    • Can we use a liquid as cathode and anode?

    • Can we use fruits or vegetables as electrolyte?

    • What if the cathode and anode are of the same material? Will that work?

    • The observation tables have been appended at the end of this guide.

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    • In the tactivity, you have made a battery using two 10 cm long pieces of magnesium. What would happen if one 20 cm long cell was made?

    • Will this 20 cm long cell be sufficient to power an LED? What do you think?

    • Let's make one and find out!

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    • Cut out a 20 cm long strip of magnesium ribbon and both halves of a filter paper.

    • Wrap the filter paper (both halves) around the magnesium ribbon, leaving about 1.5 cm of ribbon bare.

    • Wrap a 20 cm long copper strip around the ribbon leaving the bare part as it is and leaving an extra 1.5 cm of copper free at the other end.

    • Now add the electrolyte and check if it can make a red LED glow.

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    • Does the longer cell generate a larger voltage? What did you think?

    • Try using different combinations of lengths of cell, like 5 cm and 10 cm in series etc to see if that makes a difference.

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    • What do you think will happen if an iron nail is used instead of the magnesium ribbon? Will this setup be able to glow an LED?

    • Will it take more or less number of cells to make a single red LED glow?

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    • Cut a circular filter paper in half and and wrap it around the iron nail leaving the a part of the nail near its head uncovered.

    • Take a copper strip of 8-9 cm in length and wrap it around the filter paper. The copper strip should not be in contact with the iron nail at any point in the cell. If the strip is too long, make it shorter so that it fits.

    • Place the cell in the citric acid solution you had made earlier and make sure the filter paper absorbs the solution.

    • Connect the positive end of the LED to the copper strip an the negative end to the iron nail.

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    • Does the LED glow with one cell?

    • Try making 3 more cells with the iron nails. Connect them in series by touching the first cell's copper to the second's iron, the second's copper to the third's iron and the third's copper to the fourth's iron.

    • Now connect the positive terminal of the LED to the copper of the fourth cell and the negative of the LED to the iron of the first cell.

    • Does the LED glow now? How about with 3 or 2 cells in series?

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    • Until now, we have been using citric acid as the electrolyte.

    • What if we use some other solid or liquid as the electrolyte? Will the battery still work?

    • Try creating your own new electrolytes and test them out.

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    • Follow steps 1-7 provided in the guide.

    • After performing step 7, add your electrolyte to the cells instead of citric acid solution.

    • Then connect two of the cells in series as done in step 5 and connect the positive terminal of the LED to the copper and the negative terminal of the LED to the magnesium.

    • Here, we have used copper sulphate as the electrolyte, but you may choose any soluble salt, acid or base as your electrolyte, e.g. common salt (sodium chloride), vinegar (acetic acid), slaked lime (calcium hydroxide), and many other options...

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    • What are the different electrolytes you have tried?

    • Which ones make the LED glow and which don't?

    • Does using no electrolyte also work?

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    • You can also check which variation will make an LED glow for a longer period of time. Fill in the table with your observations.

    • If a multi-meter is available, try to find the voltages produced by the different batteries.

    • There is another activity for you. After making all the variations, connect the batteries to an LED and make it glow. Now record the time each variation makes the LED glow for. Check at various intervals, as noted in the table.

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Finish Line

Attached Documents

Kailash NR

Member since: 05/02/2017

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