DC Current: RA1, RA2, RA3, I1, I2, I3

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Homework Help Overview

The problem involves measuring direct current using ammeters with different resistances and determining the current when no ammeter is present. The subject area relates to electrical circuits and Ohm's law.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculations leading to the current values and question the validity of the approach used. There are inquiries about the expected results with different ammeter resistances and the relevance of circuit modeling in this context.

Discussion Status

Some participants are seeking clarification on the original poster's calculations and reasoning. There is a suggestion to show work for better understanding, and a few participants emphasize the importance of sketching the circuit for clarity.

Contextual Notes

There are mentions of circuit relevance and the necessity of visual aids in understanding the problem, indicating a potential gap in the original poster's approach to the problem setup.

gruba
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Homework Statement


When direct current is measured with ammeter of resistance RA1=100mΩ, current is I1=12 A. When direct current is measured with ammeter of resistance RA1=50mΩ, current is I2=15 A. What is the value of current if there is no ammeter (RA3=0)?

Homework Equations


Ohm's law

The Attempt at a Solution


I am getting that I3=18 A. The result should be 20 A.

Could someone check this?
 
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How did you get 18 A?
It is hard to find a mistake if you don't show your work, but here is a guess: using your approach, what would you expect for an amperemeter with a resistance of 1 Ohm? Is that result realistic? If not, something is wrong with the approach.
 
gruba said:

Homework Statement


When direct current is measured with ammeter of resistance RA1=100mΩ, current is I1=12 A. When direct current is measured with ammeter of resistance RA1=50mΩ, current is I2=15 A. What is the value of current if there is no ammeter (RA3=0)?

Homework Equations


Ohm's law

The Attempt at a Solution


I am getting that I3=18 A. The result should be 20 A.

Could someone check this?
What electrical circuit have you sketched to use as a model for the unknown circuit where you are trying to measure current?
 
NascentOxygen said:
What electrical circuit have you sketched to use as a model for the unknown circuit where you are trying to measure current?

In the question, circuit is irrelevant.
 
gruba said:
In the question, circuit is irrelevant.
Show how you worked out your answer, then.
 
gruba said:
In the question, circuit is irrelevant.

whenever you have a physical problem, unless it is trivial, it is always a good idea to make a sketch.
 
+1 to that. Not sure I could do it without making a sketch diagram but then I'm old.
 

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