How Much Saltwater Would it Take to Run a Nightlight?

Ions and Electricity

• The process of making a light bulb glow is complicated and involves confusing words such as ions, conductors and currents. Put simply, electric charge follows a current, or path, through a conductor. A conductor is any substance that allows the current to move freely. Conductors receive help from ions, which are atoms with a charge. An ion has either a positive or a negative charge. That electric charge passes from ion to ion inside the conductor and along the current. The most common process is through wires or cords, like those on the computer and plugged into a socket. The charge moves through the cord and into the computer.

Saltwater as a Conductor

• Regular table salt contains two elements, sodium and chloride. Together the elements are neutral, and salt does not contain ions. Add the salt to water, and the water molecules rip the elements apart. When separated, the sodium has a positive charge and the chloride has a negative charge. This creates many ions that float freely and turn the water into a conductor. To harness the power in the saltwater, it is necessary to build a circuit to aid the flow of electricity.

Building a Circuit

• Allow the child to make his own nightlight with adult supervision. Wrap two tongue depressors in aluminum foil and use wires to connect one depressor to the light bulb socket and the second depressor to a 9-volt battery. Attach a final wire from the light bulb socket to the battery. This creates a circuit through which the current travels. The charge passes from the battery through the depressors and then to the bulb, before continuing around the loop again. Press the two depressors together so they touch to see if the light bulb glows. If it does, the circuit works. If not, reattach the wires and try again.

Lighting the Circuit

• The bulb glows only when the two depressors are touching so the charge passes through them. Use saltwater to make the bulb glow without the depressors touching. Fill a cup with distilled water and dissolve 1 teaspoon of salt in the water. Dip the two depressors into the water, so they do not touch, and watch the light bulb shine. The charge passes from one depressor into the ions in the water, through the second depressor and lights the bulb.

Considerations

• The more salt in the water, the stronger the bulb glows. A larger bulb requires more salt than a tiny bulb. Over time, the salt will dissolve in the water and the bulb won't light. Replace the water every night to ensure the nightlight keeps working. It is possible to light a bulb without the battery, but it would take lots of salt and the bulb would not glow but a few moments. Saltwater nightlights can help kids learn to sleep in the dark. Start with plenty of salt in the water for a bright light, and over time lessen the amount of the salt so the light becomes dimmer. Continue using less salt until the child no longer needs a nightlight.