How to Make a Resistivity Water Tester
You can construct an apparatus to test the resistivity of water to know how well it conducts electricity. You will find that water is a fairly poor conductor of electrical current, but it does so slightly due to impurities. While resistance and resistivity both measure a material's ability to limit current flow, resistivity takes into account the size of the material as well. The higher an object's resistivity (measured in ohm-meters), the harder it is for electricity to flow through the object.
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Things You'll Need
- Rectangular glass dish
- Tape measure
- Calculator
- 9-volt battery
- Electrical wire
- Duct tape
- Digital multimeter
Instructions
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1
Measure the depth, width and length of the glass dish in inches. For example, you might have a dish with a depth 3.0 inches, a width of 12.0 inches and a length of 18.0 inches.
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2
Convert the dimensions of the glass dish to meters by dividing by 39.37, since a meter contains 39.37 inches. Performing this step leads to a depth of 0.076 m, a width of 0.305 m and a length of 0.457 m.
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3
Multiply the depth by the width to obtain the area of the short sides of the glass dish in square meters. Continuing the example, you have 0.076 m times 0.305 m, or an area of 0.023 square meters.
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4
Connect a wire to the positive lead of a 9-volt battery and another wire to the negative lead. Tape the other ends of the wires to the opposing short ends of the glass dish. Make sure the end of the wire faces the bottom of the dish and is about an inch deep into the dish.
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5
Fill the glass dish with water. Make sure to cover the ends of the submerged wires. Turn on the digital multimeter and move the measurement dial to the resistance setting. Resistance is measured in ohms, designated by the capital Greek letter omega (Ω) on some multimeters. Place the red (positive) lead of the multimeter in the water close to, but not touching, the positive wire from the battery. Place the black (negative) lead of the multimeter in the water close to, but not touching, the negative wire from the battery. Record the resistance of the water in ohms. For example, the resistance might be 5.0 megaohms or 5,000,000 ohms.
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6
Multiply the resistance by the area and then divide by the length of the dish. This yields the resistivity of the water in ohm-meters. Continuing the previous example, 5,000,000 ohms times 0.023 square meters and divided by 0.457 meters equals 251,641 ohm-meters.
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Tips & Warnings
Resistivity calculations require metric units for measurements.
A megaohm equals one million ohms.
References
Resources
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