Question
A given galvanometer is to be converted into (i) an ammeter (ii) a milliammeter (iii) a voltmeter. In which case will the required resistance be (i) least (ii) highest and why?
✓
Answer
The required resistance has least value in the case of an ammeter and maximum value in the case of a voltmeter.
This is due to the reason that the shunt resistance required to convert a galvanometer into ammeter or milliammeter has the value.
$\text{S}=\frac{\text{I}_g}{\text{I}-\text{I}_\text{g}}\times\text{R}_\text{g}$
Thus, the shunt required in the case of milliammeter has higher value.
Similarly, since the voltmeter should have a high resistance, the value of required resistance should be highest in the case of a voltmeter. This is connected in series with the coil of the galvanometer.
This is due to the reason that the shunt resistance required to convert a galvanometer into ammeter or milliammeter has the value.
$\text{S}=\frac{\text{I}_g}{\text{I}-\text{I}_\text{g}}\times\text{R}_\text{g}$
Thus, the shunt required in the case of milliammeter has higher value.
Similarly, since the voltmeter should have a high resistance, the value of required resistance should be highest in the case of a voltmeter. This is connected in series with the coil of the galvanometer.
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