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

[gruba]

Homework Statement

When direct current is measured with ammeter of resistance R_A1=100mΩ, current is I₁=12 A. When direct current is measured with ammeter of resistance R_A1=50mΩ, current is I₂=15 A. What is the value of current if there is no ammeter (R_A3=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?

 

[mfb]

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.

 

[NascentOxygen]

Homework Statement

When direct current is measured with ammeter of resistance R_A1=100mΩ, current is I₁=12 A. When direct current is measured with ammeter of resistance R_A1=50mΩ, current is I₂=15 A. What is the value of current if there is no ammeter (R_A3=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?

 

[gruba]

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.

 

[NascentOxygen]

In the question, circuit is irrelevant.

Show how you worked out your answer, then.

 

[William White]

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.

 

[CWatters]

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