Voltmeter in series?

Abstract

A recent physics challenge shows a circuit, where a voltmeter is connected in series. Indeed, real voltmeters have finite input resistance, therefore one may think that they can be used as resistors. In addition, voltmeters measure the voltage difference between their terminals, therefore it seems to be possible to calculate the current flowing through them. Is it okay? Does it make the voltmeter more universal? Are there any hidden secrets? How it is related to high-quality physics and STEM education, which are increasingly important in the modern world? Doesn't it approve an improper use that one can never see in any textbook and application? Suggesting and teaching such uncommon solutions doesn't generate undesired attitude? On the other hand, can it make the development of creativity and understanding harder if the students are taught to follow always the application rules? We do think it bears some discussion.

Phonocardiography and Photoplethysmography With Simple Arduino Setups to Support Interdisciplinary STEM Education

“…Students are rarely able to find the reasons of such problems due to the lack of in-depth knowledge and understanding, therefore they often try to find a case with reckless trials when it seems to work. This is one example of the worst attitudes that can be developed [6], [43].…”

“…Even if an improper method produces accurate enough output in certain cases, it does not mean that it is acceptable. High-quality education should always follow the well-established rules of technology [43].…”

Comment on ‘Resistance of a digital voltmeter: teaching creative thinking through an inquiry-based lab’

“…One may say that it is not a serious concern in a school experiment, the readings are accurate enough. It is not a problem if the accuracy is not high, but we do think that students should be taught that any instrument has its specified accuracy what should always be kept in mind [2,4]. They should be able to calculate the error of the measurement.…”

A novel measurement technique for DC voltage and current reducing the DMM loading effects

“…According to the technique proposed herein, when the variable of interest is a current (voltage), instead of connecting an ammeter (voltmeter) in series (parallel), a voltmeter (ammeter) and then an ohmmeter are connected in series (parallel) at the same two terminals conventionally employed. The fact of connecting a voltmeter in series was already suggested in [10], but not with the aim of decreasing the loading effects of instrumentation. The experimental results presented later show that loading effects are reduced by a factor of at least 100 but up to 500 when applying the novel technique.…”