Changes between Version 26 and Version 27 of ElectricalIntroduction

Timestamp:

Aug 26, 2017, 2:34:32 PM (8 years ago)

Author:

David Albert

Comment:

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ElectricalIntroduction

@@ -71 +71 @@
 When electrons are allowed to flow between the positive and negative battery terminals, we have a *circuit* and the battery's chemical reaction proceeds (until the chemical reaction is complete).  The number of electrons flowing between the terminals is called "Current" and is measured in [https://en.wikipedia.org/wiki/Ampere Amperes] aka Amps (named after [https://en.wikipedia.org/wiki/Andr%C3%A9-Marie_Amp%C3%A8re André-Marie Ampère].  The number of electrons flowing depends on how many electrons the battery can supply (how fast the chemical reaction can proceed) and the nature of the path carrying the electrons from one terminal to the other.  
 The electron flow generated by a chemical battery or a solar cell is always from one terminal to the other; this is called ''Direct Current'' or ''DC''.  Electricity can be generated in other ways such as turning an electromagnetic generator (alternator in your car, steam turbines in a power plant, etc.); when generated in this way, electrons are alternately pushed then pulled by the same terminal of the generator which is called ''Alternating Current'' or ''AC''.  The electricity from a wall outlet is alternately pulled/pushed 60-times per second.
+
+The amount of current a battery can supply (it's capacity) is often measured in Amp-Hours.  This is useful because the battery voltage is fixed by its chemistry; the size and construction of the battery determine how much current it can provide and for how long before it is depleted.  For example, the lead acid batteries used on the peanut robots typically are rated for 7 Amp-Hours (often abbreviated Ah).  This mean the battery can supply 1A of current for  7 hours before it is used up and needs to be recharged (or 2A of current for 3.5 hours or 7A of current for 1 hour, etc.).  If you've taken calculus, you'll recognize the power consumed by a battery as the area under the curve formed by current consumed vs. time; the Ah capacity of the battery is the total area under that curve.
 
 You can can measure DC and AC current flow using your multimeter in the next section.