# Working out the shunt resistance for a galvanometer circuit

## 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

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kuruman
Homework Helper
Gold Member
The shunt should be in parallel with the galvanometer, not in series. See here.

etotheipi
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
Homework Helper
Gold Member
How are ##I## and/or ##I_g## in part 1 related to ##I## in part 2?

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
Homework Helper
Gold Member
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 ..."

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