Galvanometer (resistance G, full-scale deflection current $I_g$) is converted to: Ammeter (measuring current I): connect shunt resistance S = G*$\frac{I_g}{I - I_g}$ in parallel. The shunt carries most of the current, protecting the galvanometer. An ideal ammeter has zero resistance. Voltmeter (measuring voltage V): connect high resistance $R_s$ = $\frac{V}{I_g}$ - G in series. An ideal voltmeter has infinite resistance. Loading effect: a real ammeter (finite R) reduces the current slightly; a real voltmeter (finite R) draws some current, reducing the measured voltage. JEE may ask for the shunt or series resistance, or for the error introduced by the instrument.