The amperage describes the electric current

which is passed through a circuit or appliance. It is measured in A ampere,

or coulombs per second. The electric current is the flow of electric charge in

form of ions or electrons. Voltage and resistance of the circuit alter the

amount of electric current which can flow through the circuit; their correlation

is described in Ohm’s law:

: voltage;

: resistance;

: ampere

Ampere is measured by connecting an ampere

meter in series with a resistor. They are connected in series, so that all of

the current flows through the ampere meter.

If the circuit is closed without a resistor

connected in series to the ampere meter the short-circuit current (I0)

is measured. The short-circuit current is the maximum amount of electric

current which can be produced by the galvanic cell, since no resistor is

connected in series, there is no resistance, except the internal resistance of

the galvanic cell itself and the negligible resistance of the ampere meter

(approximately 15 mV). Therefore, all of the voltage drops at the internal

resistance (except for a negligible amount at the resistance of the ampere

meter) and thus the limiting factor for the amperage is only the reaction rate

and the movement of the ions towards the electrodes.

3.2.3 Resistance

Resistance is like a counter force to

voltage, voltage is the potential difference and resistance is a measure of the

difficulty to pass an electric current through a resistor. If a resistor has a

low resistance, a voltage is able to move a certain amount x/t of electric

charge through the resistor, but if the resistance is increased the same

voltage can only move a lower current through the resistor. The resistance is

determined by two properties, the material and the shape of the resistor.

The internal resistance of a galvanic cell

is defined by two properties, by the surface of the electrodes, the area where

reactions can take place, and the difficulty to move electrons, respectively

ions, from one electrode through the electrolyte to the other. In a closed

circuit there is also voltage drop at the internal resistance, for this reason

galvanic cells are supposed to have a low internal resistance, so that all of

the voltage can be utilized in the circuit.

The internal resistance can be measured

with an ohm meter or calculated by subtracting the measured voltage from the

open-circuit voltage and then multiplying by the measured amperage.

: internal resistance;

: open-circuit voltage;

: voltage;

: amperage