Finding current in an electric circuit

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Homework Help Overview

The discussion revolves around calculating the current in an electric circuit using a voltmeter with a specified resistance. The circuit includes a cell with an electromotive force of 5.0 V and a resistor, raising questions about the effects of the voltmeter's internal resistance on the measurements.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the calculation of current using the formula I=V/R and express confusion regarding the voltmeter's internal resistance. There are questions about how to incorporate this resistance into the calculations, and some participants clarify the role of the voltmeter's resistance in circuit measurements.

Discussion Status

The discussion is ongoing, with participants exploring the implications of the voltmeter's internal resistance. Some have offered clarifications regarding the resistance values and their relevance to the problem, while others are still grappling with the initial assumptions made in the calculations.

Contextual Notes

Participants note that the voltmeter's resistance is specified as 50kΩ, which is a point of confusion for some. There is also mention of the design purpose of voltmeters to minimize circuit disturbance, leading to further questions about practical limitations in measurement.

ImpCat
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Homework Statement


A voltmeter of resistance 50kΩ is used to measure the electric potential difference in a circuit, as shown. The cell has an electromotive force (emf) of 5.0 V and negligible internal resistance.

upload_2016-12-1_8-38-49.png


Homework Equations


I=V/R
V=IR

The Attempt at a Solution


I=5/150000 I=3.33E-5
V=50000*3.33E-5=1.7 V

But the answer is 1 V. How?[/B]
 
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You did not account for the internal resistance of the voltmeter.
 
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Doc Al said:
You did not account for the internal resistance of the voltmeter.

How do you account for the internal resistance of a voltmeter though? It's not provided. Plus isn't voltmeters purposefully created with high resistance so as to create as little change in the circuit as possible?
 
ImpCat said:
How do you account for the internal resistance of a voltmeter though? It's not provided. Plus isn't voltmeters purposefully created with high resistance so as to create as little change in the circuit as possible?
You're told it is 50kΩ. (That's separate to the resistor of the same value in the circuit.)

There may be reasons it can't always designed to be near "infinity".
 
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NascentOxygen said:
You're told it is 50kΩ.

There may be reasons it can't always designed to be "infinity".

Ohhhh I see, I thought the 50kΩ is the resistance of the resistor! Maybe I should've read the question more clearly. :woot:
 
See my amended reply.
 
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