Electronics > Beginners
Some noob questions
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PA4TIM:
Buy the Art of electronics, this is one of the best books about electronics. It goes very deep. If I'm correct it was written for university use. Buy the third edittion. The difference with the 1980's second edition is huge. (I have second and it still is my bible)

A DMM has an input resistance. The bad ones a few Mohm, the very good ones over 10 Gohm. So there is always a small current flow through your meter (and so influencing the circuit  ;) ) . But there are electrometers and that is a different beast. They measures the electric field.

A voltage exist without any current flow, all it needs is one point that is more positive charged as an other point. If you connect those points a current will flow.

Measuring a voltage is not so easy as many people think. You disturb the circuit and for some things the meter is the wrong type. A nice example: If you connect a diode between the battery and a DMM you will measure the voltage of the battery minus the voltdrop of the diode. That is f.i. if you use a normal 10Mohm (or less) . If you measure it with a 10G meter or electrometer  the current is to small to bring the diode in forward conduction and you measure the electric field. 
Here I show some things that can go wrong while measuring a voltage. (i have also a video over pittfalls for small current measurements.)
https://youtu.be/bH5n5iMIqIw
rstofer:

--- Quote from: Mr D on July 21, 2018, 01:53:56 pm ---
Wait, nope, i still don't understand. Is it possible to measure the current without knowing BOTH the voltage and resistance?

Or put another way: to measure either, voltage, current or resistance, you ALWAYS need to know the other two? Or is one ever enough?

--- End quote ---

There are 3 variables for Ohm's Law (E, I, R) and you need to know two to calculate the 3rd.
rstofer:
This might be a worthwhile program but it costs a few bucks (I just signed up, it cost me $15):

https://www.eevblog.com/forum/beginners/beginners-that-are-interested-in-learning-electronics-from-the-ground-up-)/

This program is MASSIVE!  There are 134 lectures totaling 86+ hours!

The author has published quite a few books in addition to this program.  The books are available on Alibris.Com - just search by Author.

Price seems to be flexible.  The landing page says $20 but when I checked out it was $15, probably because I have bought other programs.  So, maybe it costs $20 to a newcomer.  It's a BARGAIN!  I have smoked parts that cost more than that!

Mr D:
@PA4TIM, nice, will check out your videos!

@rstofer, thanks, but that link you posted doesn't go anywhere, could you try again?
rstofer:

--- Quote from: Mr D on July 21, 2018, 05:51:08 pm ---@rstofer, thanks, but that link you posted doesn't go anywhere, could you try again?

--- End quote ---

It's another thread in the Beginner's Forum and I'll be darned if I can link it.  So, here is the Udemy link
https://www.udemy.com/crash-course-electronics-and-pcb-design/

I don't know why I can't link the thread but the title is correct and it's just a few items down this page.
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