# basic voltage query

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#### Albert Symes

Joined Oct 22, 2015
41
got a question i cant find the answer to,can anybody help.cheers

a 12v dc supply is connected to 2 100k resistors in series.a voltmeter has sensitivity of 10,000 per volt is swithed to its 10v range,

2) the percentage error of meter reading in part (1)

#### StayatHomeElectronics

Joined Sep 25, 2008
1,073

#### Albert Symes

Joined Oct 22, 2015
41
got a question i cant find the answer to,can anybody help.cheers

a 12v dc supply is connected to 2 100k resistors in series.a voltmeter has sensitivity of 10,000 per volt is swithed to its 10v range,

2) the percentage error of meter reading in part (1)

#### WBahn

Joined Mar 31, 2012
29,533
10,000 what per volt? Cats? Geraniums?

Since this is homework, you need to show YOUR best attempt to solve YOUR homework problem. It doesn't have to extensive or correct, but you need to give us something to start from. We aren't going to just work your homework for you.

#### Albert Symes

Joined Oct 22, 2015
41
12 x 10,000 ohm =120,000 /10 = 12000 v

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#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
It's not a well-formed question.
e.g. The voltage across the 12 V source is 12 V/

They probably want the voltage across one resistor. You also have to assume that the the voltage source is ideal. You can only measure one resistor at a time.

So find the voltage across the resistor with no meter.

Use the ohms/V relation to figure out what the meter's resistance would be at that voltage.
ohm/V * Volts = ohms(meter)

Calculate it again with the calculated resistance in parallel with 100K.

#### WBahn

Joined Mar 31, 2012
29,533
12 x 10,000 ohm =12,000 /10 = 1200 v
12 x 10,000 ohm = 120,000 ohm, it most certainly does not equal 1200 V.

#### Albert Symes

Joined Oct 22, 2015
41
your right,i humbly apologise for that mistake

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#### WBahn

Joined Mar 31, 2012
29,533
your right,i humbly apologies for that mistake
Not a problem -- take another shot at it.

Hint: Be sure to get the correct units for the meter sensitivity and then track the units through your work -- most mistakes can be caught that way.

#### Albert Symes

Joined Oct 22, 2015
41
12v x 10,000 ohm =120,000 /10 = 12000 v

#### WBahn

Joined Mar 31, 2012
29,533
12v x 10,000 ohm =120,000 /10 = 12000 v
Again,

12 V x 10,000 ohm = 120,000 ohm

It does NOT equal 120,000/10.

Even if it did, 120,000/10 = 12,000 and NOT 12,000 V.

And what is this 12000 V supposed to be? The reading on the voltmeter? Does that make any sense whatsoever?

You haven't yet indicated how the voltmeter is connected to the circuit. Don't make us guess.

What is the definition of the sensitivity for a voltmeter? What are the proper units for it?

Don't guess -- look it up.

#### Albert Symes

Joined Oct 22, 2015
41
voltmeter has sensitivity of 10,000ohm per volt

#### WBahn

Joined Mar 31, 2012
29,533
Okay. So the sensitivity of your voltmeter is 10,000 Ω/V.

Now, what does this mean? What IS voltmeter sensitivity? What does it tell you?

#### JoeJester

Joined Apr 26, 2005
4,390
Here is your problem:

This happens to be a favorite question of mine.

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#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
I pretty much gave you how to do it. I just didn't do it for you.

#### Albert Symes

Joined Oct 22, 2015
41
100,000

#### Albert Symes

Joined Oct 22, 2015
41
thanks for the drawing,thats pretty handy

#### JoeJester

Joined Apr 26, 2005
4,390
So ... What are the answers.

You could have done the same drawing.

#### Albert Symes

Joined Oct 22, 2015
41
100,000 ohms

and 10%

I think

#### WBahn

Joined Mar 31, 2012
29,533
100,000 ohms

and 10%

I think
Don't just "think" up an answer. Analyze the circuit and determine the answer!

And SHOW YOUR WORK!

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