Electricity: Magnetic and Heating Effects · Lesson 5 of 7
How Electric Cells Produce Electricity
“Look inside a simple electric cell to see how electrodes, an electrolyte and chemical reactions produce current.”
• Explain how chemical reactions inside a Voltaic cell produce electric current. • Identify the roles of electrodes and the electrolyte in an electric cell. • Describe why a cell eventually stops supplying electricity. • Explain how a simple lemon cell can be constructed from two different metals and an electrolyte. • Interpret LED polarity and the use of multiple simple cells in a circuit.
Electricity from Chemical Reactions
Cells and batteries are portable sources of electricity. Inside a simple Voltaic or Galvanic cell, electricity is produced by chemical reactions involving two different metal electrodes and an electrolyte. This allows the cell to supply current to an external circuit.
An electrode is one of the metal rods or strips that takes part in the working of a cell and is partly dipped in the electrolyte.
An electrolyte is the conducting liquid or moist material in a cell that takes part in the chemical process. In a simple Voltaic cell it is usually a weak acid or salt solution.
How a Voltaic Cell Works
The two electrodes are made from different materials and are partly immersed in the electrolyte. Chemical reactions between the electrodes and the electrolyte produce electrical energy. When the external circuit is complete, current flows from the positive terminal through the circuit to the negative terminal.
- Two different metal electrodes are placed in an electrolyte.
- Chemical reactions occur involving the electrodes and electrolyte.
- The cell develops positive and negative terminals.
- When an external circuit is completed, electric current flows through it.
- As the chemicals are gradually used up, the cell becomes unable to supply current.
Why a Cell Becomes 'Dead'
A cell cannot keep supplying electricity forever. As it operates, the chemicals taking part in its reactions are gradually used up or changed. When the cell can no longer supply useful electrical energy, it is commonly described as 'dead'. This does not mean that every material inside it has vanished; it means the cell can no longer perform its electrical job effectively.
Luigi Galvani observed muscular movement when a frog's leg was touched with two different metals. Alessandro Volta argued that the source of electricity was the combination of different metals and a conducting liquid. His experiments led to the first battery.
Making a Simple Lemon Cell
A lemon can provide the electrolyte needed for a simple cell because its juice can conduct as part of the chemical process. A copper wire or strip and an iron nail act as the two metal electrodes. Several lemons can be connected so that the cells work together to power an LED.
An LED allows current through it only in the suitable direction. If it does not glow in the simple cell setup, reversing its connections may correct the polarity. In the chapter's setup, the longer LED lead is connected toward the positive terminal and the shorter lead toward the negative terminal.
The chapter lists several possible electrode pairs for simple Voltaic cells, including zinc/copper, zinc/silver, aluminium/copper, iron/copper, magnesium/copper and lead/copper. Their behaviour depends on the chemical properties of the metals.
Problem
Two metal strips are placed in a lemon and connected to a circuit. Why is the lemon juice important?
- 1.The metal pieces serve as electrodes.
- 2.The lemon juice acts as the electrolyte.
- 3.The chemical interaction involving the electrodes and electrolyte makes it possible for the cell to produce electricity.
Quiz
What produces electricity in a Voltaic cell?
What is the electrolyte in the lemon-cell activity?
Why are two different metal electrodes used in the simple cell?
Why might an LED fail to glow even when the cell arrangement is otherwise working?
Why does a Voltaic cell eventually stop working?
Practice Problems
- Draw or describe a simple Voltaic cell and label its two electrodes and electrolyte.
- Explain the sequence from chemical reaction inside the cell to current in the external circuit.
- Describe how you would build a simple lemon cell using copper and iron.
- An LED does not glow when connected to several lemon cells. What simple change should be tried first, and why?
- Explain what is meant when a single-use cell is described as 'dead'.
Key Takeaways
• A Voltaic cell converts chemical energy into electrical energy through chemical reactions. • Two different electrodes and an electrolyte are essential parts of the simple cell described in the chapter. • Current can flow through an external circuit when the cell is connected correctly. • A lemon can act as the electrolyte in a simple classroom cell. • A cell stops working effectively when the chemicals needed for its reactions are used up or changed.