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Ohm's Law: Procedure

Procedure

As you move through the following steps, observe what is happening inside the gel box!

Record your data on the Activity Sheet that follows.
  1. With the power supply OFF, connect the empty gel box to the power supply.

  2. Set the lo/hi switch (if present on your power supply) to LO, turn the power supply ON, and select a potential of about 100V (volts). Record (on your Activity Sheet in Table 1) the current (measured in milliamps) generated in the empty gel box and any other observations (bubbles, color changes, temperature). Does current flow through air? Does that mean there is a high amount or low amount of resistance?

  3. Turn the power supply OFF.

  4. Open the gel box, and add about 300 mL of distilled water. Turn the power supply ON. With a potential of 100V, record (in Table 1 AND Table 3) any observations and the level of current in the box. Does current flow through distilled water? Does that mean there is a high amount or low amount of resistance?

  5. Turn the power supply OFF.

  6. Add 1 mL of the sodium chloride solution to the distilled water in the box. Carefully "slosh" the box to mix the salt and water. Turn the power supply ON . Set the voltage to 100V. Record (in Table 1 AND Table 2 AND Table 3) the current and other observations. Does current flow through distilled water that contains ions (Na+Cl-)?

  7. Choose 7 additional voltages (both lower and higher than 100 volts) and record (in Table 2) the current and other observations at each voltage. Turn the power supply OFF.

  8. Add another 1 mL of the sodium chloride solution to the distilled water in the box. Carefully "slosh" the box to mix the salt and water. Turn the power supply ON . Set the voltage to 100V. Record (in Table 1 AND Table 3 the current and other observations.

  9. Add 1 mL of the sodium chloride six more times, each time "sloshing," then recording the resulting current in Table 3. DO NOT FORGET TO TURN OFF THE POWER SUPPLY EACH TIME BEFORE YOU OPEN THE GEL BOX.

  10. Clean up: Turn the voltage to 0 volts, set the HI/LO switch to LO and turn off the power supply. Open the gel box, disconnect the lid and pour out the buffer. Rinse the box twice with tap water and put it upside down on a paper towel to dry. DO NOT ATTEMPT TO DRY OUT THE INSIDE OF THE GEL BOX. You might break the expensive electrode wires!

Upon completion of this lab

  • Dispose of designated materials in the appropriate places.
  • Leave equipment as you found it.
  • Check that your work station is in order.
  • Wash your hands.


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