Hubber and Kirkwood have used the following diagram to outline the way a dry cell functions (Skamp, K (Ed.), 2004, pp 131-135).
According to Hubber and Kirkwood:
- A dry cell has a metal casing which contains chemicals held in a paste.
- The metal casing has two separate parts known as terminals. One terminal is positive (+) and the other is negative (-).
- The positive terminal has a steel disc and a bump on it. It is connected to a carbon rod located in the middle of the battery.
- The negative terminal is a flat steel disc that connects to a zinc casing.
- A manganese dioxide and ammonium chloride paste separates the carbon rod from the zinc casing.
- A complex chemical reaction occurs inside the cell which causes a number of negatively charged electrons from the positive terminal to be deposited on the negative terminal. As a result, the positive terminal is left with a greater number of positively charged protons (ie, a positive charge). The negative terminal which has more negatively charged electrons is left with a negative charge.
- The chemical reaction inside an isolated cell reaches a state of equilibrium which leaves a small charge on each terminal. This occurs because "electrons have the same electric charge and so will repel each other. The chemical reaction can't keep moving electrons to places where an excess number of electrons already exist" (Skamp, K., 2004, p132).
The illustration below was obtained from www.odec.ca/.../2006/glaz6j2/battery_info.htm (accessed 04/09/2009). This is an "experimental" website containing basic battery information and activities. The illustration is more detailed than the diagram above and shows how the carbon rod does not connect to the negative terminal. It also indicates that terminals are also known as electrodes. Furthermore, it identifies a positive electrode as a cathode and a negative electrode as an anode. 
The illustration above also helps to explain how a circuit disturbs the equilibrium in a cell and allows the chemical reaction to continue. In the 3rd edition of Teaching Primary Science Constructively, Hubber and Kirkwood provide a good summary of how this occurs(Skamp, K (Ed.), 2008, pp 127 - 132):
- When a metal wire connects a cathode and anode, an (unbroken) pathway is formed.
- The pathway is called "an electric circuit, or more precisely, a closed circuit".
- If the pathway is broken, it is a “open circuit”.
- Electrons are part of all atoms that make up ALL substances, but generally they are not free to move away from the atoms they are attached to. In some substances, including metal, electrons are free to move (“free electrons”). Such substances are called “conductors”.
- Substances with electrons that are not free to move are called ‘insulators” (eg plastic).
- When a closed circuit is formed, an electric field is created which provides a pathway for the electrons to move from the negative terminal along the wire to the positive terminal. This movement of electrons disturbs the equilibrium and allows the chemical reaction to deposit more electrons on the negative terminal which in turn move along the pathway.
Hubber and Kirkwood provide a good summary of the following terms (Skamp, K (Ed), 2008, pp 130-131):
Voltage - "The voltage of the battery gives a measure of the strength of the electric field which pushes the free electrons around the closed circuit". As such, a 6-volt battery gives four times the push of a 1.5-volt battery on free electrons.
Electric current - the flow of electrons is called the electric current. The greater the voltage in a closed circuit, the greater the electric current.
Energy transformations and transfers in a torch- "The energy in the chemicals of the battery (chemical energy) is transformed into motion energy of the electrons. As they speed around the closed circuit they collide with the atoms in the filament in the globe thus transferring their motion energy to the atoms. This causes the atoms to vibrate. The vibrating atoms transform their motion energy into heat and light energy".
Electric current, resistance and power in the torch - "The size of the current is also affected by the ease with which the free electrons are able to move in the circuit. In the torch circuit, the filament does not provide an easy path for the free electrons as the wire of which it is made is much narrower than the other wires in the circuit".
Power - the term power "relates to the rate at which energy is transformed in the electric circuit. The unit of power is the Watt, where 1 watt represents 1 joule of energy being transformed per second". A 100W light bulb transforms 100 joules of electrical energy into light and heat energy every second the light globe is operating".
Hubber and Kirkwood provide a good summary of how energy, voltage, current, resistance and power are related (Skamp, K (Ed.), 2008, p131). This summary refers to a closed cell in a torch, but equally applies to other circuits. As mentioned they use the term battery for a cell. That said, this summary applies to both cells and batteries:
- The battery voltage determines the amount of energy given to each electron; the higher the voltage the greater the energy.
- The battery voltage and resistance in the circuit determine the size of the electric current; greater currents occur with larger battery voltages and/or less circuit resistances.
- The amount of energy transformed at the globe depends on the amount of resistance the globe has compared to the rest of the circuit. In a torch circuit, most of the free electrons' energy get transformed in the globe as it has most of the circuit resistance.
- The rate at which energy is transformed in the electric circuit is the power.
Hubber, P., & Kirkwood., V. (2008). Shining a light on electricity. In Skamp, K (Ed.), Teaching Primary Science Constructively (3rd Ed., pp125-154), South Melbourne, 2008.
Hubber, P., & Kirkwood., V. (2004). Shining a light on electricity. In Skamp, K (Ed.), Teaching Primary Science Constructively (2nd Ed., pp127-173), South Melbourne, 2004.
