Param Himalaya - परम हिमालय

Voltmeter : A voltmeter is an instrument used to measure the potential difference across the two ends of a circuit element.  Conversion of galvanometer into voltmeter :  A galvanometer can be converted into a voltmeter by connecting a large resistance in series to the galvanometer. Let G and R be the resistance of a Galvanometer and a conductor connected in series with it respectively. Let V volt be the potential difference to be measured by the voltmeter.Let $I_{g}$ be the current flowing in the circuit . Now potential difference between points A and B is given by : $$V = I_{g}R + I_{g}G$$ $$V = I_{g}(R+G)$$ $$\therefore \ R + G = \frac{V}{I_{g}}$$ $$R = \frac{V}{I_{g}}-G$$ Effective Resistance of the voltmeter :  Effective value of resistance of the galvanometer is given by : $$R^{'} = (R+G)$$ Which is very High Thus , voltmeter is a high resistance device , Resistance of an ideal voltmeter is infinite. Note : a voltmeter is always connected in parallel to the circuit c...

An ammeter is an instrument used to measure electric current in an electric circuit. A ammeter is a modified form of a galvanometer for measuring current in the circuit we require a device of a very low or practically zero resistance. Conversion of Galvanometer into Ammeter : "A Galvanometer can be converted into an ammeter by connecting a low resistance ( called shunt) parallel to the galvanometer."  A small resistance S (shunt resistance) connected in parallel to galvanometer (G) is shown in figure.  Let G and S be the resistance of a galvanometer and shunt respectively. Let I be the total current to be measured by an ammeter in the circuit.  Let $I_{g}$ be the current flowing through the galvanometer. The remaining current $(I-I_{g})$ flows through the shunt resistance.  Since G and S are parallel, the potential difference across them is same.  $$(I-I_{g}) S=I_{g} G$$ $$S = \left (\frac{I_{g} }{I-I_{g} } \right )G$$ This is the required value of shunt resist...