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bigplanet401
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Homework Statement
I am taking a class in circuit analysis and am trying to measure the internal resistance of the Radio Shack multimeter. The internal resistance (unknown) is R_x. A battery (with voltage V_s) is available along with a resistor R that has the same order of magnitude of R_x.
Homework Equations
Kirchhoff's voltage law (KVL)
The Attempt at a Solution
I tried using the circuit shown in the attached file and connected it in the way shown below the circuit. Before making any connections, I tried to figure out what the voltages would be.
I think the voltage across R should be V_s because of KVL around the loop containing the battery and the resistor.
By applying KVL around the loop containing the multimeter, I get the following equation:
V_x + V_s = v
(V_x is the voltage across the internal resistance of the meter.)
But when I hook up the circuit, the voltage v is less than V_s, which would mean that V_x is negative, right? This does not make sense to me. It looks like R_x and R are in series, which, if V_x was positive, would mean that I could write something like
[tex]
v \frac{R}{R+R_x} = V_s
[/tex]
which would mean
[tex]
R\left( \frac{v}{V_s} - 1 \right) = R_x
[/tex]
But because v is less than V_s, the parenthesized expression is negative and R_x is negative, which can't be true. Any advice?