Voltmeter is a device used to measure pd between two points in a circuit. Voltmeter is connected in parallel between the points whose pd is to be measured. The introduction of voltmeter should not alter the pd or current in the circuit. Ideally voltmeter should not draw current from the circuit. Hence an ideal voltmeter should have infinite resistance.
A galvanometer can be converted into a voltmeter by connecting a high resistance in series with it. Let maximum safe current through a galvanometer of resistance G be Ig and the voltage to be measured is V. Then the series resistance required is calculated as follows:
pd across voltmeter = max. Voltage
ie Ig(G+R)=V
or R= V/Ig -G
Thus a galvanometer of resistance G and safe current Ig can be converted into a voltmeter to read a maximum voltage of V by connecting a series resistance of value R=V/Ig -G
A galvanometer can be converted into a voltmeter by connecting a high resistance in series with it. Let maximum safe current through a galvanometer of resistance G be Ig and the voltage to be measured is V. Then the series resistance required is calculated as follows:
pd across voltmeter = max. Voltage
ie Ig(G+R)=V
or R= V/Ig -G
Thus a galvanometer of resistance G and safe current Ig can be converted into a voltmeter to read a maximum voltage of V by connecting a series resistance of value R=V/Ig -G
nice
ReplyDelete