| Farad: | The S.I.unit of capacitance, defined as the capacitance of a capacitor that, if charged to 1 C, has a potential difference of 1 V. |
| Faraday: | The electric charge required to liberate gram equivalent of a substance. 1 Faraday = 96485 coulomb/mole. |
| Fermat's principle: | An electromagnetic wave takes a path that involves the least time when propagating between two points. |
| Fluids: | Matter that has the ability to flow. |
| Focus: | The point to which rays that are initially parallel to the axis of a lens or mirror are converged or from which they appear to diverge. |
| Fraunhoffer lines: | The dark lines in the spectrum of sun. |
| Free fall: | The motion of a body under the effect of gravity alone. |
| Frequency: | The number of oscillations completed in 1 second by an oscillating body. |
| Fundamental frequency: | The lowest frequency at which a system vibrates freely. |
