Biophysics has many different sources of energy, which involves converting forms of energy into electrical and magnetic energy, or vice versa. The following list covers a few of these common energy sources that are used in our society:

  • Photovoltaic cells: More commonly known as solar cells, they absorb sunlight and produce electricity. The process of a p-n junction semiconductor absorbing photons and creating a current is called the photovoltaic effect, hence the name photovoltaic cell.

    A p-n junction is formed when a p-type semiconductor is brought into contact with an n-type semiconductor. N-type semiconductors have electrons (negative charge carriers) as their conducting charge carriers, whereas p-type semiconductors have holes (positive charge carriers) as their conducting charge carriers. The light (more technically called the photon) absorbed close to the junction creates a conduction hole and conduction electron pair, and the two can then travel off in their respective materials creating a current in the circuit. Semiconductors are critical in almost all electronic devices.

  • Photosynthesis: The photon energy causes an electron to be ejected from a molecule, causing the molecules in the plant to be ionized by the photons. Ultimately, the photon energy is converted to chemical energy through a sequence of interactions. In green leafs the chlorophyll will absorb a photon and release an electron if the light is red or blue-violet. However, if the light is close to green, then it will not absorb the light but just reflect the light, which is why leaves are green.

  • Light-emitting diode (LED): The LED is the reverse process of the photovoltaic effect; a current brings conduction holes and conduction electrons together at the p-n junction. They recombine at the junction and lose energy in the form of light.

  • Fuel cells: They produce electricity through chemical reactions. For example, the fuel is ionized and the electrons flow from one pole through an electrical circuit to the other pole while the ionized fuel interacts with an oxidizing agent such as Oxygen (O2) in the air. The chemical reaction produces an electrical current and excess energy.

  • Batteries: They’re similar to fuel cells in that chemical energy is being converted into electrical energy. However, the chemical reaction continues within the battery even when no current is being produced within the circuit, whereas within fuel cells, the chemical reaction is halted when no fuel is being supplied to the cell. The batteries are usually split into two types:

    • Non-rechargeable: The non-rechargeable batteries have chemical reactions that are usually difficult (or dangerous) to reverse.

    • Rechargeable: An input of energy will easily reverse the chemical reaction within the rechargeable battery.

  • Power stations: They convert mechanical energy into electrical energy. The mechanical energy does work on a generator, which produces electricity via Faraday’s law.

    The source of the mechanical work is varied; the four primary sources are

    • Fossil fuel: The fossil fuel power stations are typically coal burning, oil, and natural gas.

    • Nuclear: The nuclear power stations typically use enriched uranium or uranium with heavy water.

    • Hydro: Hydro dams require damming the rivers, and the water flows down the penstock and then through large turbines.

    • Wind: The wind farms are similar to the hydro dams except air is turning the large blades.