Why Is My Circuit Showing Higher Current Than Expected?

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  • Thread starter Thread starter driedupsharpie
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Discussion Overview

The discussion revolves around unexpected current readings in simple DC circuits set up by a college student. Participants explore potential reasons for the higher-than-expected current values based on Ohm's Law, including equipment calibration and measurement accuracy.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Homework-related

Main Points Raised

  • The original poster reports consistently higher current readings than expected based on voltage and resistance values.
  • Some participants suggest that the measurements of voltage, current, or resistance may be incorrect or that there could be a combination of inaccuracies.
  • One participant questions the calibration of the lab equipment and the specifications of the resistors used.
  • Another participant emphasizes the reliability of Ohm's Law and suggests that the unexpected results indicate some inaccuracy in the setup.
  • There is mention of the possibility of using different measuring devices and resistors to verify the results.

Areas of Agreement / Disagreement

Participants generally agree that there is likely some inaccuracy in the measurements or equipment, but no consensus is reached on the specific cause of the higher current readings.

Contextual Notes

Limitations include potential inaccuracies in measurement devices, the condition of the resistors, and the calibration status of the power sources. The discussion does not resolve these uncertainties.

Who May Find This Useful

Students and beginners in electronics who are learning about circuit behavior and measurement techniques may find this discussion relevant.

driedupsharpie
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My first post on the forums, go easy on me...

So I'm getting a feel for the new lab my college has and all of the equipment in it so I thought I'd set up some VERY simple circuits just to get used to some of the DC power sources (there are a few different ones).

No matter what I do though, the current always seems to be slightly HIGHER than the expected value coming from the given voltage and resistance.

For example: I'll set up V = 10v R = 10Ω and get values above the expected (slightly)
I'll hit 1 amp @ 9.8 volts
I hit 1.1 amps @ 10.75 volts
I hit 1.2 amps at 11.7 volts

Any idea what seems to be causing this simulated lower resistance?
 
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driedupsharpie said:
No matter what I do though...

Including measuring the same setup with a different voltmeter and ammeter? And trying different 10 ohm resistors?
 
A 9.8 ohm resistor? Obviously the voltage, current, or resistance measurements are incorrect, or any combination of the three. Not that I'm really telling you anything you don't already know. :) Are there any lab standards, recently calibrated supplies or meters, 1% or 0.1% resistors. Is your lab near the Mystery Spot in Santa Cruz California?
 
driedupsharpie, Welcome to Physics Forums!

Both Nugatory and meBigGuy have offered good suggestions to explain your unexpected readings. My suggestion is this: When just starting out in electronics place your trust...all your trust...in Ohm's Law! It has held true in every single test ever performed with it so far. So, there is some inaccuracy in your setup: either the current reading, the voltage reading, or the resistance value is faulty. One of these is giving you "unexpected results".

Now, once you discover that Ohm's Law is reliable, you may continue onward to more complex circuits knowing that the fundamentals are totally under control. This is the foundation you rest on while ascending the complexity ladder of electronics.

Cheers, Bobbywhy
 

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