How Does a Voltmeter's Resistance Affect Voltage Measurement Accuracy?

[rey242]

Homework Statement

A voltmeter will be used to measure the voltage vA in the circuit below. Assume that the voltmeter has a resistance of 100[ohms] and a full-scale voltage of 20[V].

a) What will the voltmeter read?
b) What is the percentage error in making this reading?

Homework Equations

Several equations
(i.e KVL, KCL, Ohm's law, Voltage Divider, Current Divider, etc.)

The Attempt at a Solution

I have a general idea on how to do this but I'm not sure if about a few concepts...
I'm pretty sure that there is no current through the 7 volt source.
I think you can figure Vb can be figured out through KVL but I am not sure.
If I cant, then I have to use one part of the circuit to find vb.

Can you check to see if these concepts are correct?

 

[phinds]

You MUST show some work (calculations). We can't help if we don't know exactly where you are stuck and forum rules prohibit our just giving you an answer.

 

[Babadag]

In my opinion you have to find a relationship between 3Vb and Vb.

Also, you have to know how to compare the voltmeter readings with the actual voltage which you have to find.

 

[DaveE]

When you are making a voltage measurement, the voltmeter becomes part of the circuit. So, draw it in on the schematic to include its effect.

 

[phinds]

Since the OP hasn't been here in 10 years I doubt we are going to get an updated drawing. I made my post as part of a general cleanup we are doing on old posts and to alert new members who find this post via a Google search that we require some work.

 

[Babadag]