Measuring voltages question

dk345 · 24 Apr 2011 at 18:52

My brother has asked me to help him with his electronics work. But I have no idea really. There must be someone in OcUK's massive pool of knowledge that knows the answer, because now it's starting to annoy me.

Say I have this circuit:

http://img717.imageshack.us/i/circuit.png/

Where R1 and R2 are resistors rated at 1000 Ohms and the voltmeter is an ammeter rated at 10mA, I need to work out the voltage at point P. But how do I do it? Is it some application of Kirchoff's Law, or is it just plain Ohms law, or is it something entirely different?

Any input, please?

Nix · 24 Apr 2011 at 18:55

Lick your finger and touch it.

p4radox · 24 Apr 2011 at 18:56

It's just a potential divider. You can derive this from Kirchoff and Ohm but the simplest thing to remember is that the voltage is shared between the resistors like:

V = Vs x R/(R+R)

So V = Vs/2

Or in words: the resistors are equal, so half the supply voltage is dropped across each of them.

dk345 · 24 Apr 2011 at 19:06

Nix said:
Lick your finger and touch it.

He said he'd already tried that in the lab practical, it didn't work

p4radox said:
It's just a potential divider. You can derive this from Kirchoff and Ohm but the simplest thing to remember is that the voltage is shared between the resistors like:

V = Vs x R/(R+R)

So V = Vs/2

Or in words: the resistors are equal, so half the supply voltage is dropped across each of them.

Thank you very much, that makes sense to me so I'm sure it'll make sense to him. Much simpler than I was thinking actually. Cheers.