The potential difference between the terminals of a dry cell is about 1.5 volts (abbreviated V), regardless of the size of the cell. The potential difference depends only on the chemicals used in making the cell. The size affects only the length of time required for discharge.
Dry Cell Size
The larger the volume of a dry cell, the longer its life for a given ad. The lie is longer because the cell has a greater capacity for chemicals. Increasing the volume of chemicals provides more time before the chemicals are used up. You can see the comparison of sizes of 1.5 V 6V and 9V dry cells.
Higher potential differences can be achieved by connecting two or more dry cells in series. A typical flashlight, for example, may need a potential difference of 3 V cross he filament of the bulb. The potential difference is obtained by connecting two 1.5V dry cells in series. To obtain 6 V, you need four 1.5V cells. A 9 V transistor radio battery” has six cells side, each of which produces 1.5 V.
Although both the AAA and No. 6 dry cells are 1.5 V, there is a considerable difference in the amount of current and the length of service each provide. The difference in life is due to the difference volume, Smaller cells deliver less current because they have a higher internal resistance.
You may have noticed that the light from a flashlight is quite bright when you first switch it on. But the light becomes dimmer after a while. If you the flashlight off, let the cells “rest” for half an hour or so, and then turn it on again, the light again seems to be as bright as when you first turned it on.
The reason for this behavior is that the cell becomes polarized by hydrogen and ammonia gases during operation. The gases interfere with the movement of ions in the electrolyte and slow down the electrochemical action.
The polarization is reduced by manganese dioxide in the electrolyte. But the gases collect faster than the depolarizer can remove or absorb them.
However, when you turn the flashlight off, the depolarizer continues to remove the gases from the carbon electrode until polarization is no longer a problem when you turn it back on.
Dry Cell Life
The life of a dry cell depends to a great extent on the rate of discharge. Most dry cell applications require only small amounts of current for short periods of time. If the cell is required to furnish current for a long time, its life will be shortened considerably-even if the current is quite low.
Temperature effects on dry cell
The temperature of a dry cell affects its performance. Most dry cells are designed to operate best at a temperature of about 20°C (about 70°F)
- A higher temperature increases the cell’s current capacity, but it shortens the life of the cell because the electrolyte dries out faster.
- A lower temperature reduces the cell’s current capacity, because the ions in the electrolyte cannot move as rapidly from one electrode to the other.