Chapter 3.3

The Battery - Chemical Properties:

This is the schematic symbol for a battery. Take a moment and follow this link to check out The Battery

For many years the low cost acidic battery of choice for radios and electronics has been the zinc carbon battery. In recent years it has loosing ground to its competition, the alkaline battery.

Battery Types

Common commercial Dry-Cell batteries on the market today?

Zinc-Carbon Cell - Voltage 1.5 volts

When looking at the zinc-carbon battery, over the life of the cell the voltage level will start to drop off a bit. This might cause a flashlight, for example, to not be very bright after it has been used for a while. The Zinc-Carbon cell is not re-chargeable. This means the chemical reaction can not be reversed within the cell by using electricity.

The construction of the zinc-carbon cell uses an zinc outer shell material in the shape of a storage can, and is the anode of the battery. Recall that the anode is the negatively charge side of the cell. The center post, the cathode, is a type of carbon called graphite. The cathode represents the positively side of the cell. The electrolyte is an acidic type of paste which is a combination of ammonium chloride (NH4Cl) and manganese dioxide (MnO2).

       
 Chemically an oxidation reduction reaction takes place.
 Half Reaction
       2 NH4  +  2 MnO2  +  2e-  - - - >  Mn2O3  +  2  NH3  +  H2O
 Half Reaction
       Zn (s)  - - - >  Zn2+  +  2e-
 Full Reaction
       Zn + 2 NH4Cl + 2 MnO2  - - - >  ZnCl + Mn2O3 + 2 NH3 + H2O + 2e-

What this means in unscientific terms is that the battery has potential energy (2e-). It is waiting to give up this energy in trade for a chemical reaction. So when the user uses electricity, a chemical reaction takes place, moving electrons (2e-) from one plate, through the circuit and ending up with the 2e- on the other plate. That is the flow of electricity. The battery can do this until it has depleted its ability to produce this chemical reaction. This battery is then considered dead, and needs to be properly recycled.

These cells that use a zinc casing generally have a short life span due the zinc can become porous and the zinc is converted to zinc chloride. The substances within the battery are very corrosive to metals. If (and when) the substances in this type of cell start to leak out, the electrolyte can damage or destroy electronic equipment.

Check out the Alkaline Dry Cell - Voltage 1.5 volts
Check out the Nickel-Cadmium Cell - Voltage 1.2 volts
Check out the Silver-Oxide Cell: Voltage 1.6 volts

The Generator - Electromagnetic Properties:

One process of creating electricity is by generating electromagnetic electricity. In its simplest form, this is when a wire (or wire segment) and a magnetic field pass by one another. Generally the magnetic field is stationary and the wire portion of the generator moves, but this is not always the case. Many small gasoline engines have the magnet attached to the flywheel and a coil of wire is stationary.

Regardless of which part moves and which is stationary, this action is described as having a wire segment cutting the magnetic field.

To expand this process in more detail we will review the Left Hand Rule. Using ones left hand, place the hand out with the thumb pointing up (y axis) and index finger pointing straight out (x axis) at a right angle with the thumb. Now open the middle finger (z axis) to be at right angles with the index finger. The index finger represents the direction of the magnetic energy coming out of the north pole of the magnet. The thumb indicates the direction, the conductor (wire) is moving along the face of the magnetic field. The middle finger represents both the conductor and points in the direction the electrons are flowing along the conductor.

A single wire crossing a magnetic field produces such a small amount of electricity that it would be hard to measure or use in our daily activities. If we had a conductor with 5 loops of wire in a coil the result would produce 5 times more voltage than is produced in the single loop example. A 300-loop coil would produce about 300 times the voltage.

Now, if we were to put coils of wire on a shaft and mounted the shaft so it could continuously rotate inside a magnetic field we will continuously get electricity. This is exactly what happens inside a generator. Many coils of wire are wrapped around an armature (center metal component) of the generator. The north and south poles are part of the stationary or stator section of the generator.

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