Monday, June 17, 2013

Resistors in parallel, part I

So the next experiment is to place two resistors in parallel.  We start with two resistors of the same strength.

Again, I refer the reader to the HO:ME blog for further discussion of same.  They also refer to some "math" that we will get to in a bit, although probably not at this blog post.

The setup:

This first is just to document the voltage from the single AA battery. 

I then wired the circuit below, and found that as I was wiring the circuit I made a mistake in the way I wired it up.  I had everything connected, below, except for the two dotted lines.  I then had two choices, to connect via path 1 below, or path 2.  I honestly wasn't sure which, so I just did both and measured the resistance:

This is path 1, current of 162 milliAmps:

This is path 2, current of 320 milliAmps:

So right at twice the flow.  Which I thought was wrong.  What happened to the other resistor?  I had two resistors in the circuit, but it seemed that when I ran the path 1 circuit, one of the resistors was effectively cut out.

For comparison, the current just running through a single resistor is 162, same as the path 1 wiring.

So I drew this out with the path 1 section of the circuit tipped over a bit, just to help me visualize, and came up with this funny-looking triangle circuit.   It occurred to me that this triangle loop was a bit deceptive, and what I really have is two resistors in parallel.  One is the actual resistor on the up-and-back part of the triangle, and the other is just a wire.

The resistor itself is 10K ohms.  The wire, 0.4 ohms.  This, in my mind, indicated that there probably is current flowing through the resistor, but it's, oh, 5 or so orders of magnitude lower than that flowing through the wire.  No wonder it looked like I had simply cut that resistor out of the circuit.

This, then, is the diagram for path 2, which is the proper way to hook up the resistors in parallel.

A very simple circuit, which still provided ample opportunity for learning (that is, confusion that required resolution via reading and further experimentation).

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