Monday, May 02, 2016

2.1 Electromotive Force (EMF)

This week starts Module 2 of the Navy Basic Electricity and Electronics series. Last week I finished summarizing:

Module 1: Electrical Current

The second module begins with Electromotive Force (EMF) produced by chemical action. This book was written in the early 1970s so it's fun to see how out of date the batteries it has in mind are. Of course the way chemistry works hasn't changed. Here are the bullet points from the first section of this Module:
  • Electromotive force (EMF) is the force that moves electrons through a circuit, created by some source like a battery.
  • Voltage is related but slightly different. EMF is a force. Voltage is the difference of potential between the positive and negative poles of the battery or source of EMF.
  • The module references "dry cell" batteries. The figures are funny because they go back to when both the positive and negative posts of a battery were on the top, the positive in the center and a negative terminal on the outer rim of the top.
  • In that scheme, there was a center rod in a battery that was made out of something like carbon. 
  • Then the outer "electrode" on the inside of the container might be made out of something like zinc. 
  • Then a chemical paste in the middle was an "electrolyte" that facilitated an accumulation of electrons on the zinc electrode, leaving a positive charge on the carbon rod.
  • Today, of course, the most common batteries are lithium batteries.
  • So within the battery, there is the potential for an electron flow from the positive to the negative terminals of the battery.
  • Outside the battery, there is the potential for an electron flow from the negative terminal around a circuit and back to the positive terminal.
  • A "volt" is the unit of measurement for potential difference. The same metric prefix applies for volts as for amps (milli-, micro-, kilo-, mega-)
  • Batteries can be connected together in series to add up the total amount of voltage (negative to positive, negative to positive, etc).
  • When not connected properly (in series opposition as opposed to series aiding), they cancel each other out.
  • When connected in parallel, the life of the battery is increased (often done in subs, at least in days gone by).
Next Week: 2.2 Magnetism

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