All Resources

Conducting Currents

A circuit is a continuous path through which electricity travels. We usually think of this path as a wire, but believe it or not, it can also be a liquid!

To conduct electricity a substance needs charged particles that are free to move.

It might surprise you to hear that water is a poor conductor, since you've been told never to use an electrical appliance near water because of the danger of electrocution.

Absolutely pure water wouldn't let charge move through it, although it's particles are always moving, they are not charged, so it wouldn't conduct poor conductor of electric current. Everyday water around our houses or in nature always has other substances dissolved in it, and those dissolved substances may allow charge to move.

Salt is poor conductor, as its solid molecules are locked in place and cannot move.

Salt molecules are made of charged sodium ions and chlorine ions. When you put salt in water, the salt dissolved into solution. Water molecules pull the sodium and chlorine ions apart so they are floating freely. These ions are what carry electricity through water, as these charged particles can freely move.

In this demonstration, students will see how a solution can complete a circuit.

Fun Fact!
A substance may be an insulator if the voltage is low, but may conduct current if the voltage is higher. The mini-light in this circuit won't glow if there's a gap between the wires – air doesn't conduct current at this low voltage. With the higher voltages in a thunderstorm, the air molecules are ripped apart into ions and will conduct current quite well – that's why you see lightning!


Objectives

  • Describe the components required to complete an electric circuit.

Materials

  • Per Group or Student:
    3 insulated wires (about 20 cm long each)
    wire cutters
    wire strippers ( would be a good idea to have the wires cut and stripped before hand)
    1 Christmas tree mini light bulb with wire attached
    tape
    2 D-cell batteries
    bowl
    water
    salt
    teaspoon

Key Questions

  • What happens to the light bulb when we fill the bowl with water? How about salt water? How do you know?
  • What happens to the light bulb as the salt dissolves?
  • Why do you think this is happening?
  • What changes as you add more salt?
  • Why doesn’t the light bulb come on when the wire ends are in the plain water?
  • Is water a good conductor of electrical current? How do you know?
  • Is solid, undissolved salt a good conductor of electrical current? How do you know?
  • Is salt water a good conductor of electrical current? How do you know?

What To Do

Preparation:

  1. Strip both ends of the three wires as well as those attached to the mini light bulb.
  2. Twist the first wire with one of the wires of the light bulb.
  3. Twist the second wire with the second wire of the light bulb. Tape the free end of the long wire to the positive end of the battery.
  4. Place the second battery so that its positive end is touching the first battery’s negative end, and tape the batteries together.
  5. Tape one end of the third wire to the negative end of the second battery.

Demonstration:

  1. Demonstrate that the circuit is working by touching the two free ends of the wires together. The bulb should light.
  2. Place two free ends into a bag of salt, making sure that they are not touching each other. Observe that the light bulb does not come on.
  3. Bend the two free ends of the wires over the bowl and tape them in place, making sure that they are not touching each other.
  4. Fill the bowl with water, submerging the free ends of the wires. Observe that the light bulb does not come on.
  5. Add some salt to the water, one teaspoon at a time, and stir.
  6. Watch the light as the salt dissolves.

Extensions

  • Replace the bulb with an ammeter to measure how the current changes with increasing amounts of salt.
  • Investigate the particles that make up ionic substances like salt and molecular substances like water.