Biophysics For Dummies Cheat Sheet

You, like many students, may come into their first biophysics course with misconceptions. Remember these important points when you take your biophysics course to help you succeed:

• *Biophysics isn’t modular. You may think of biophysics as modular that you can break down into individual segments or parts. However, all of biophysics is connected and related, so when you’re studying a specific topic in biophysics, you should be asking yourself how it’s connected and fits with the biophysics you already know.

• Biophysics requires more than memorization. You may think memorization will help you ace the class. Although some memorization is important, memorizing a collection of formulas won’t get you through the course. Some students try to treat their biophysics as a cookbook with recipes instead of a rulebook. In fact, biophysics provides a set of rules that you can apply to many different situations throughout the life sciences.

• Formulas are finicky. Sometimes students during an examination, in desperation, write down a formula and try to use it without understanding the formula. Mathematical formulas in biophysics are shorthand notation for some physical relationship. Make sure you’re clear in your understanding of what the symbols in a formula mean.

  For example, consider the formula d = v t. In this case, d = v t can mean the distance is equal to the speed times the elapsed time, or it can mean the displacement is equal to the average velocity times the elapsed time. In general, it doesn’t mean the position is equal to velocity times the elapsed time.

• Units are your friends. Units are a set of standards for physical quantities, such as length and time. If someone says something is 1 foot (1 meter) long, then you know how long it is. If someone says something is 1 long, you do not know if it is 1 inch, 1 foot, 1 micron, or 1 meter.

  Always include your units, even within the calculations. Many students ignore the units and then add them at the end, after all the calculations are complete. For example, when working with angles, they’re sometimes in degrees and sometimes they’re in radians. Your calculator doesn’t know which units you’re working with, so you need to keep your units straight and provide the angle with the correct units to the calculator. Always carry your units throughout the calculation and treat them as algebraic quantities.

You can find many biophysics websites on the internet, with many of them focused on specific areas of biophysics. A few websites to visit initially in your search are the following:

• The Biophysical Society: This website has a career section, a job board, and links to the society’s journals and other useful information about biophysics and what biophysics is all about.

• Physics Societies/Associations: Many countries have a physics society or association. These organizations usually have divisions in biophysics, medical physics, and health physics. For example, the American Physical Society has a Division of Biological Physics.

• The Health Physics Society: Health physics deals with radiation safety and protection. This website has a career section, a job section, and links to relevant journals, information about radiation, and other useful news related to health physics and what health physics is all about.

• The International Organization for Medical Physics: This website has a news section, a career section, a job section, and lots of relevant information.

• The American Association of Physicists in Medicine (AAPM): This website has a news section, a career section, a job section, links to relevant journals, and other useful information relevant to medical physics and what medical physics is all about.

  You can find additional links on the AAPM website. This site has links to many international websites for fields related to medical physics.

• The American College of Radiology: This website has a section on medical physics.

• The International Commission on Radiological Protection: This website is helpful for obtaining the current protection standards and guidelines for radiological protection.

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 leaves 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.