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I am a high school student And we lately started studying rc and rl circuits And my questions are What is the difference between volte meter and the scope? Why we use the ground as reference in the scope but not the volte meter? Which one is the most accurate Thank you in advance

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    \$\begingroup\$ They certainly look different - have you noticed that? \$\endgroup\$ – Andy aka May 8 '15 at 17:26
  • \$\begingroup\$ The ground is the second lead of the scope's voltage-vs-time meter. Beware it may (or may not) be connected to the wall socket ground! \$\endgroup\$ – Chris Stratton May 8 '15 at 18:06
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As Alex mentioned, a 'scope is just a fast, graphical voltmeter. This concept is a bit easier to understand in an old, analog, CRT-based 'scope. They have a timing circuit that moves a single dot across the screen at a certain (adjustable and very precise) rate, while a completely separate circuit uses the input voltage to move the dot vertically. Persistence of vision completes the effect.

As a side-effect of this design, which has equivalent tradeoffs in the digital world also, oscilloscopes tend to be optimized for speed over accuracy. They're usually pretty good, but considering that even a good digital 'scope may only have 256 possible values to display, it's pretty clear that a 3- or 4-digit DMM has a pretty good chance at being more accurate than a 'scope, especially if it's been calibrated recently.

As for the grounding question, the voltmeter does have an equivalent connection. We just call it the negative probe. In a 'scope, the negatives are shared between channels and usually connected to the ground pin of the power plug, so you need to be a bit more careful with it, but it serves the same purpose otherwise.

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  • \$\begingroup\$ Persistence of vision and, persistence of the phosphor. \$\endgroup\$ – Solomon Slow May 8 '15 at 21:20
  • \$\begingroup\$ Yeah, there's that too, which is sometimes prolonged to make an analog storage 'scope, but I think POV lasts longer than unmodified POtP. \$\endgroup\$ – AaronD May 8 '15 at 21:27
  • \$\begingroup\$ radiomuseum.org/forum/tektronix_three_kinds_of_storage.html \$\endgroup\$ – Solomon Slow May 11 '15 at 13:34
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A scope is basically a voltmeter that graphs the measured voltage with respect to time. Both of them have two input leads.

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  • \$\begingroup\$ Wrt = with respect to, so it's not redundant \$\endgroup\$ – alex.forencich May 8 '15 at 17:26
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    \$\begingroup\$ @alex, it would be better to spell it out, just like we ask questions to spell things out rather than write in TXT SPK. \$\endgroup\$ – The Photon May 8 '15 at 17:31

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