Voltage of battery through voltmeter

AI Thread Summary
To determine the reading of a voltmeter across an 85 V battery with an internal resistance of 5.73 ohms and a voltmeter resistance of 482 ohms, the current must be calculated to find the potential drop across the voltmeter. The voltmeter can be treated as a resistor, allowing for the use of Ohm's law to solve for the voltage reading. For the second part, the ratio of internal resistance to voltmeter resistance must be analyzed to ensure the error in the emf reading does not exceed 5%. This involves setting up inequalities based on the potential drop across the voltmeter. The discussion concludes with the user successfully obtaining the correct answers for both parts of the problem.
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Homework Statement



A 85 V battery has an internal resistance of r = 5.73 ohms .

(a) What is the reading of a voltmeter having a resistance of R_v = 482 ohms when placed across the terminals of the battery?
___________ V
(b) What maximum value may the ratio r/R_v have if the error in the reading of the emf of a battery is not to exceed 5.0%?


Homework Equations



V=IR
V=E-Ir
V_v= I_fs ( R_c +R_s)

The Attempt at a Solution



i don't know where to start, the only thing i have tried was drawing the diagram of the circuit. please offer input on where to start thank you in advance
 
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(a) Just treat the voltmeter as a resistor. Then find the current and calculate the potential drop across the voltmeter.

(b) For this let the resistance of the voltmeter be R. Then using the same method above, determine the potential drop across the voltmeter in terms of R, f(R). Then we want 0.95(V)<|f(R)|<1.05(V) where V is the emf of the battery.
 
thank you very much i got both answers correct thank you
 
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