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Nonideal voltmeters

by evilempire
Tags: nonideal, voltmeters
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evilempire
#1
Feb1-05, 08:38 PM
P: 24
Here is the question, for reference:


A voltmeter with resistance R_V is connected across the terminals of a battery of emf E and internal resistance r. Find the potential difference Vmeter measured by the voltmeter.
Express your answer in terms of R_V, r, and E.
I have two equations but am having trouble solving them for V, clearly by eliminating I

E-(I*r)-(I*R_V)=0
V_ab=E-(I*R)

Any help would be appreciated, thanks.
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evilempire
#2
Feb1-05, 09:12 PM
P: 24
Nevermind, I got it, but the next problem is giving me a bit of trouble:

If E = 7.5 volts and r = .45 ohms, find the minimum value of the voltmeter resistance R_V for which the voltmeter reading is within 1.0% of the emf of the battery.

I am given the following equation to work with:

E(1-(r/(r+R_V))
evilempire
#3
Feb1-05, 09:18 PM
P: 24
Nevermind, got that too. Disregard this thread, heh.


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