A moving coil galvanometer is a sensitive device which can be used as a detector to check if a curretn is flowing in a circuit. A galvanometer works on the principle that a current carrying coil placed in a radial magnetic field experiences a deflecting torque whose magnitudes is directly proportional to the electric current passing through it. The deflection `phi` is indicated by a pointer and is give as `phi = (NAB)/k cdot I`.
A galvonometer can be used to measure electric current flowing througha circuit direcly in ampere and its submultiples. For this purpose we join a small resistance `'r_s'` in parallel to the galvonometer. Such a shunted galvonometer is called an ammeter. If a galvanomter, having a resistance `R_G`, givens full scale deflection for a current `I_g` and we want to measure a current ranging from `0 - I_g A`, then the value of shunt resistance will be
`r_s = (R_G cdot I_g)/(I - I_g)`

If you want to measure a current ranging 0 - 1.5 A using the above galvonometer. What shunt resistance should be joined with it ? Resistance of galvanometer coil is `300 Omega`.

Explanation

Shunt resistance `r_s = (R_G.I_g)/(I - I_g) = (300 xx (600 xx 10^(-6)))/(1.5 - (600 xx 10^(-6))) = 0.12 Omega`