A chemical cell converts chemical energy into electrical energy, whereas a solar cell converts energy from electromagnetic radiation into electrical energy. Both act as sources of electromotive force (emf) in a circuit and usually produce direct current.
This is part of IB Physics B.5 Current and circuits and applies to both SL and HL.
How Each Cell Works
A cell's emf is the energy transferred by the source per unit charge:
An emf of , for example, means that the source transfers of energy per coulomb of charge passing through it.
| Feature | Chemical cell | Solar cell |
|---|---|---|
| Initial energy source | Chemical energy stored in reactants | Energy carried by incident electromagnetic radiation |
| Energy conversion | Chemical energy to electrical energy | Radiation energy to electrical energy |
| Mechanism | Chemical reactions separate charge and establish a potential difference | Absorbed photons transfer energy within the material, allowing charge carriers to be separated |
| Operating condition | Operates while suitable chemical reactants remain | Produces electrical output while sufficiently illuminated |
| Typical output | Direct current | Direct current |
In both cases, charge is already present in the conducting circuit. The cell establishes a potential difference, causing mobile charge carriers to move when the circuit is complete.
A common misconception is that a cell continuously creates charge. It does not: electric charge is conserved. The cell transfers energy to existing charge carriers. Another misconception is that a solar cell stores sunlight; it normally converts incoming radiation directly, although its output can be stored separately in a rechargeable chemical battery.
Exam Technique
For an IB explain question, identify the original energy store and state the energy conversion for each cell. Do not merely say that both “make electricity”; use emf, energy transferred per unit charge, and conservation of charge where relevant.