Electrolytes, conductivity, and resistance
Conductivity is the ability for materials to allow the flow of electrons, ions, or both. This movement of charged species is generally known as current, and the prevention or inhibition of current is known as resistance. Even when there are ions in solution, resistance still exists, and there are limitations to the amount of current that can flow. This resistance causes the charged species to separate over some distance and creates a potential (also known as voltage). Increasing the concentration of ions reduces resistance. Conductive metals such as silver, copper, and gold have negligible resistance to the flow of electrons; therefore, resistors are always included in circuits to control the voltage and the relationship among these can be specified as
V=IR
where V represents voltage (in volts, V
), I represents current (in amperes, A
), and R represents resistance (in ohms, \Omega
).
Batteries are constructed to have an internal resistance that produces a known potential, which is why consumer batteries are rated at 1.5 V
, 9 V
, 12 V
, etc. The following describes what happens when a circuit is shorted: A lower resistance pathway is introduced to a designed circuit, and electric current would flow through that new pathway instead since electrons and ions always travel the path of least resistance, and both the resistance and voltage would be considerably reduced (and they can even approach values of zero).
Part D
In the PhET simulation, click the Macro menu in the top left corner of the screen. Notice the circuit available in the Conductivity tab on the right side of the screen. This circuit contains a negative electrode (green bar), a positive electrode (red bar), a battery, and a light bulb. Drag this circuit to the beaker. Notice that you can change the length of the wire for both the electrodes by dragging them up or down (providing images with wire lengths changed). Sort the following submersion scenarios according to whether they will result in a short circuit, a completed circuit that conducts electricity, or an incomplete circuit that does not conduct electricity.
Drag the appropriate items into the respective bins.