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Minor Versionm

by Kailash NR


Make a conductive paint and use it to create your own resistor.

    • Scissors have functional sharp edges. Contact may result in injury.

    • Always keep blades away from fingers and body. Handle with care.

  1. To make the battery holder please visit this link DIY Battery holder - Foam and Spring.
    • The longer leg is the positive terminal.

    • Connect the wire from the negative terminal of the battery to negative terminal of the LED.

    • Attach another wire to the positive end of the LED. Keep the other end free.

    • Remove insulation from both the ends of the wires before you connect to LED or battery.

    • Keep the wire from the positive end of the battery free.

    • We are going to use the free ends to check the conductivity of different materials.

    • You can also keep a longer wire ready to attach it on the positive end. This is only useful for checking bigger objects.

    • The wires are now your test leads.

    • Use these test leads to test various materials for their conductivity. Never bring the test leads in contact with each other; keep them at least 2-3cm apart on every object that you test.

    • If the LED does not glow, it is an example of a negative result, in this case the material is an insulator.

    • If the LED glows, it is an example of a positive result, in this case the material is a conductor.

    • The connections between the battery and safety pin might be loose, in that case hold the two terminals with your thumb and index finger for a better connection.

    • Make sure all the connections are clean and stable, otherwise the current will not flow.

    • To ensure proper connection, wind the wire several times over the material.

    • Does the brightness of the LED vary among different conductors?

    • Conductivity is directly proportional to brightness of the LED. (True/ False)

    • Are all metals conductors, and all non-metallic substances insulators? (Yes/No)

    • Can an LED be connected in any direction and still work? Can you think of any other use for this property of the LED?

    • Why is it important to connect the batteries as we did here? Are there other ways of connecting multiple batteries?

    • Use the observation table shown alongside to classify the materials into good and bad conductors and insulators.

    • Good conductor - LED glows brightly. Bad conductor - LED glows dimly. Insulators - LED does not glow.

    • Try to check some bigger materials like iron rod, bicycle wheel rim, cricket bat etc.

    • Try to check the conductivity of liquids like milk, curd, lemon juice or any other fruit juice.

    • If you want to check the conductivity of even more materials, please click on this link Electrical Conductivity (Variations).

    • Be mindful of the battery terminals, they can heat up or momentarily spark if an electrical short occurs.

    • Start with about half gram of graphite power in a small saleable container.

    • To this add 2 drops of white (PVA) glue.

    • Use the dropper to measure out 1 ml of water and add it to the mixture.

    • Use the dropper to stir the mixture till it's of an even consistency and is free of lumps.

    • The paint is now ready to use. For long term storage, dilute it with more water and store in an air tight container.

    • You'll need an ice-cream stick and two pieces of copper tape that are 2.5 cm each.

    • Peel the paper cover off the tape to expose the stick side.

    • Stick the tape on one end of the ice-cream stick .

    • Wrap the tape around and stick it back to itself.

    • Repeat the same steps to tape the other end of the stick as well.

    • Measure out 0.5 ml of the paint with the dropper.

    • Carefully draw a line from one copper strip to the other, dispensing most of the paint as you do so.

    • Make sure both ends of the paint line touch the copper strips.

    • Now smear out the paint on the surface of the stick till there is a uniform and uninterrupted trail of paint between the copper strips.

    • Cover about half the width of the tape pieces with paint as well. This will ensure good electrical contact between the copper terminals and the graphite.

    • Now leave the stick undisturbed to dry, this can take upto an hour, depending on the ambient temperature . When its done the graphite layer will be more grey than black in colour and have a slight metallic glint to it.

    • Set up the conductivity probe as shown in this guide. This is a simple circuit consisting of an LED that will help test the conductivity of the strip.

    • Close the circuit with no load connected, just to get a feel for the maximum brightness of the LED.

      • If you are using a Red LED with brand new (unused) batteries, it is recommended that you do not perform this check as the LED may burn out.

    • Connect the two leads of the tester to the copper strips on either end of the stick. The LED should be illuminated, if a little dimly.

    • LED connected directly.

    • LED connected through the graphite stick.

    • The connections between the battery and safety pin might be loose,in that case hold the two terminals with your thumb and index finger for a better connection.

    • Make sure all the connections are clean and stable, otherwise the current will not flow.

    • Ensure proper connection to the copper contacts.

Finish Line

Kailash NR

Member since: 05/02/2017

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