Working out the shunt resistance for a galvanometer circuit

[Bolter]

Homework Statement

Find shunt resistance

Relevant Equations

Ohm's law

Here is the problem

I have tried to draw the set up for both cases which the question had described above, and came to these 2 equations. But I can't see how it would help me to work out the resistance of the shunt?

Any help would be really great! Thanks

 

[kuruman]

The shunt should be in parallel with the galvanometer, not in series. See here.

 

[Bolter]

The shunt should be in parallel with the galvanometer, not in series. See here.

Ok I have made the changes to set up 1 and get these equations now

 

[kuruman]

How are $I$ and/or $I_g$ in part 1 related to $I$ in part 2?

 

[Bolter]

How are $I$ and/or $I_g$ in part 1 related to $I$ in part 2?

Sorry I believe the I value in part 1 to be different to the I value in part 2?

To go about this question, I know that the voltage of the cell stays fixed in both cases. So could I find an expression for V in both part 1 and 2. Then equate them and solve for R_sh (the shunt resistance). I don't think this would be right as I would have more than 1 unknown there

 

[kuruman]

Sorry I believe the I value in part 1 to be different to the I value in part 2?

To go about this question, I know that the voltage of the cell stays fixed in both cases. So could I find an expression for V in both part 1 and 2. Then equate them and solve for R_sh (the shunt resistance). I don't think this would be right as I would have more than 1 unknown there

It's not the voltages that you should set equal. Reread the sentence that starts with "When the shunt is removed ..."

 

[Bolter]

It's not the voltages that you should set equal. Reread the sentence that starts with "When the shunt is removed ..."

OK I have had the time to rethink about this problem again. And I have redrawn the circuits again. This time I made use of Kirchhoff's 2nd law to help me

I got a shunt resistance of 20 ohms here?

 

[kuruman]

That's what I got.