0
$\begingroup$

I saw a definition of a parallel circuit as a circuit with more than one path for current to flow. Is that the definition that's accepted? It seems like a good definition to me, but does that mean this circuit:
resistor with voltage probe in circuit with cell
is series because the current doesn't flow through the voltmeter (in theory)?

The definition is quite good because this circuit:
same circuit with voltmeter removed, just showing break in circuit
I would say is a series circuit and the definition works for that, but I don't see much of a difference between the two circuits, so if the second one is a series circuit is the first one also series?

Edit, for clarity - The question:
What is the definition of a parallel circuit and does that make the first circuit (with the voltmeter) a series or parallel circuit?

$\endgroup$
  • $\begingroup$ Current doesn't flow through an ideal Volt meter. $\endgroup$ – Solomon Slow Oct 13 '15 at 17:14
  • $\begingroup$ @jameslarge thanks for your comment. I'm actually wanting to know if the first circuit is a series or parallel circuit, not about the resistance of the voltmeter. Thanks for your help. $\endgroup$ – Jamie Twells Oct 13 '15 at 17:17
  • 1
    $\begingroup$ I would not describe a circuit as either "series" or "parallel". Two or more two-terminal components are arranged in serial if the current that flows through one has no other path but to flow through the next (and, the next and, the next,...) Two or more two-terminal components are wired in parallel if they are wired (like all of the components in your first example) such that they must all see the same voltage across their terminals. But like Sharan Kumar said (below), when you're talking about a complete circuit, the labels "series" and "parallel" don't always fit. $\endgroup$ – Solomon Slow Oct 13 '15 at 18:39
  • $\begingroup$ @jameslarge hmm yes neither would I but unfortunately I have to teach it to high school students so I wanted to know what the real definition was. $\endgroup$ – Jamie Twells Oct 13 '15 at 22:21
1
$\begingroup$

Assuming that you are asking about the first circuit without the voltmeter is Series or Parallel -- it can actually fit both definitions. With only two elements in a circuit like that, you cannot distinguish between parallel and series.

For example, one way to find multiple element parallel circuits is that the potential difference across the parallel circuits is the same. In a series circuit, the potential difference across each element depends on the resistance (in this case as a DC circuit) of each element.

About voltmeters. Almost all (maybe all) DVM meters today are high impedance for measuring voltage. High may mean a million or multiple million ohms. My Fluke Model 189 DVM has a voltage measure impedance of 10 megohms. If the branch impedance of the element you are measuring with such DVMs is much smaller than the DVM impedance then the current flow through the meter is negligible.

Back before DVMs, the typical high impedance meter used was the VTVM or Vacuum Tube Volt Meter which is essentially a vacuum tube version of the solid state used in today's DVM.

But, other meters, such as a Triplett Analog meter back in the 1960s had an impedance measured as 20,000 ohms per volt. This told you the amount of current that was flowing through the meter of the circuit you measured and from this you could calculate the error caused by the meter's placement measuring the voltage. Cheap (back in that day) analog meters would have a impedance as low as 5000 ohms per volt (or, maybe smaller).

$\endgroup$
  • $\begingroup$ Thanks for your answer, yes I'm asking about the first circuit, with the voltmeter. $\endgroup$ – Jamie Twells Oct 13 '15 at 17:31
  • $\begingroup$ All voltmeters operate in parallel to the element voltage they are measuring. All current meters operate in series to the element they are measuring. $\endgroup$ – K7PEH Oct 13 '15 at 17:34
1
$\begingroup$

A circuit can't always be classified as series or parallel. The concept simply does not apply in general. In the first circuit, it can be said that voltmeter is parallel to the load.

$\endgroup$
  • $\begingroup$ Two good examples (though you can convert between them) are: Delta and Wye circuits. Delta & Wye circuits are not calculated using the standard series or parallel circuit formulas. Typically, you solve the Y-circuit by converting a Delta to a Wye (aka Y-circuit). Other combinations that are not solvable by direct application of series and parallel circuit formulas are Wheatstone Bridge problem, cube of resistors problem. Usually, application of symmetry, Kirchhoff's Laws, and Series/Parallel circuit formulas are needed. $\endgroup$ – K7PEH Oct 13 '15 at 19:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.