Ohm's Law: Overview and Objectives
Background
Before learning about Ohm's Law, it helps to become familiar with the power supply
and gel box. The electrode at which electrons enter the gel box from the power supply
(along the black wire) is called the cathode, and is negative (-). The electrode at which electrons leave the box and re-enter
the power supply (along the red wire) is called the
anode
and carries a positive charge (+). The flow of electrons sets up a potential energy
difference between the electrodes. This is known as
electrical potential, and is measured in volts. It establishes an electric field through which the ions in the gel box fluid migrate.
The migration of ions in the fluid creates electrical
current
which is measured in milliamperes (milliamps) which measures the rate of flow of electrons.
Resistance, measured in ohms, indicates how easily the current can flow through the gel box
fluid. The higher the resistance, the harder it is for the ions to migrate across
the box.
Ohm's Law describes the relationship between voltage, current, and resistance, named
after Georg Ohm, a German physicist born in the 18th century. Using a gel box and
power supply, it is possible to determine Ohm's Law. This can be done by keeping
the resistance constant while varying the voltage, and measuring the resulting current.
The data from that process can be plotted on a graph and then compared with other
graphs to find the equation which corresponds. The same process can also be used
by keeping the voltage constant while varying the resistance and measuring the resulting current.
Purpose
This laboratory explores the concept of Ohm's Law and teaches analytical skills by
having students derive Ohm's Law from their observations.
Materials per team
| |
power supply |
sodium chloride solution [1M] |
rack for NaCl, if needed |
| |
gel box |
300 mL distilled water |
beaker for used tips |
| |
p1000 micropipet/tips |
beaker for measuring water |
paper towels/Kimwipes |
- You can substitute other measuring instruments (droppers, pasteur pipets, regular
pipets). Volumes are approximate.
CAUTION
- Study the gel box. It is designed so that when the box is opened, the electrodes
are disconnected.
- Slide the lid of the gel box off by using the small finger hold "mounds" on the
top of the lid.
DO NOT, repeat, DO NOT PULL ON THE WIRE LEADS TO REMOVE THE TOP!!!
- Since any wet surface can
become conductive, it is advisable
NOT
to
touch
any part of the apparatus (gel box, wires) while the power supply is on. This is
especially important if the outside of the box is wet, or if your hands are wet.
Procedure
Activity Sheet
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