# Galvanometer problems

I figured out the capacitor/charging problem that I last posted. Here's my latest cause of worry:
1)The Resistance of the coil of a pivoted-coil galvanometer is 7.92 Ohms and a current of .0194 A causes it to deflect full scale. We want to convert this gavanometer to an ammeter reading 10 A full scale. The only shung available has a resistance of .0436 Ohms. What resistance R must be connected in series with the coil?

I used the equation (Ifs)(Rc)=(Ia-Ifs)Rsh, where Ifs = .0194, Rc=7.92 Ohms, Ia=10 A. I then solved for Rsh and subtracted .0436 (the shunt available) from it. Why do I not get the correct answer?

2) A 150 V voltmeter has a resistance of 15000 Ohms. When connected in series with a large resistance R across a 105 V line, the meter reads 57 V. Find the resistance R.

Any help would be appreciated...Thanks!

## Answers and Replies

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Integral
Staff Emeritus
Gold Member
The addition resistance that you are looking for is in series with the COIL not the shunt. So replace RC in your expression with a resistance equivalent to the one you need to balance the Right hand side. so instead of RC use:
Re=RC+Rs

Where Rs is the additional series resistance.

Integral
Staff Emeritus