Hi,
On 30/03/18 11:00, Alessandro Selli wrote:
Il giorno Fri, 30 Mar 2018 09:32:13 +0200
Edward Bartolo<edb...@gmail.com> ha scritto:
On 29/03/2018, Simon Hobson<li...@thehobsons.co.uk> wrote:
Edward Bartolo<edb...@gmail.com> wrote:
What you wrote reminded me of a dangerous filter that consists of two
high voltage series-connected capacitors connected in parallel with
the mains with their middle point earthed. Since these capacitors are
almost certainly the same value they will devide the mains voltage by
two. This fact can be verified with a high impedance voltmeter
connected with the disconnected earth connector and one terminal of
the mains supply.
Yes. Doesn't need to be that high an impedance meter either, a while ago
(as part of a discussion in another forum) I just did a quick check with
a basic digital multimeter and measured about 95V on my Macbook Pro. And
as I mentioned, there's enough current there to be able to feel it.
When I was studying Physics for my A Levels and at university, all my
professors insisted upon using high impedance voltmeters. A cheap
digital voltmeter/multimeter can easily have an impedance of a few
megaohms which is quite high.
I remember, once I had a practical Physics experiment that involved
getting the characteristics for a transistor. My fellow students used
old moving coil voltmeters and got terrible results. I asked to be
granted permission to use a digital voltmeter for the experiment and
got excellent results for all three characteristics. After, that the
university physics lab was equipped with new digital voltmeters.
When I was doing the same kind of studies and lab sessions we were
purposely given analog voltmeters and our task was to:
1) rate the voltmeter's internal impedance;
2) measure resistors' impedance;
3) apply the necessary corrections to the mearurements in (2) to get much
better than "terrible" results.
The point was that on students more emphasis was put in learning the right
procedures and to discern and correct the various factors that affect lab
equipment correctness rather than getting the best results in the shortest
and easiest possible way, which is what professionals are expected to do when
they carry out their duties.
Alessandro
I also learned physics through an open university, but i never did such
experiment.
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