# Homework Help: Current question

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1. Aug 22, 2015

### gruba

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1. The problem statement, all variables and given/known data
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)?

2. Relevant equations
Ohm's law

3. The attempt at a solution
I am getting that I3=18 A. The result should be 20 A.

Could someone check this?

2. Aug 22, 2015

### Staff: Mentor

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.

3. Aug 22, 2015

### Staff: Mentor

What electrical circuit have you sketched to use as a model for the unknown circuit where you are trying to measure current?

4. Aug 23, 2015

### gruba

In the question, circuit is irrelevant.

5. Aug 23, 2015

### Staff: Mentor

6. Aug 23, 2015

### William White

whenever you have a physical problem, unless it is trivial, it is always a good idea to make a sketch.

7. Aug 24, 2015

### CWatters

+1 to that. Not sure I could do it without making a sketch diagram but then I'm old.