Liquid Resistors

Project Number: 34

Description: Build the circuit, set the meter (M6) to the 0.5mA setting, and set the slide switch (S5) to position B. Add about 1/4 of an inch of water to a cup or a bowl. Connect the jumper wires to the circuit as shown and place the loose ends in the water, and make sure the metal parts aren't touching each other. Measure the current through the water. Add salt to the water and stir to dissolve it. The current should be higher now, since salt water has less resistance than plain water. If the current is too high to measure on the 0.5mA scale, then switch to the 50mA scale. Now add more water to the cup and watch the current. If you have some distilled water, then place the jumper wires in it and measure the current. You should measure close to zero, since distilled (pure) water has very high resistance. Normal water has impurities, which lower its resistance. Now add salt to the distilled water and watch the current increase as the salt dissolves! You can also measure the current through other liquids. Don't drink any water or liquids used here.

Snappy: Pure water has very high resistance because its electrons are tightly held in place. Impurities (such as dissolved dirt, minerals, or salt) decrease the resistance because they have loose electrons, which disrupt the structure and makes it easier for other electrons to move through.