An ammeter is obtained by shunting a 30 Ω galvanometer with a 30 Ωresistance. What additional shunt should be connected across it to double the range ?

For ammeterS=igi−ig×G∴ SG=igi−ig or GS=iig−1or 3030=iig−1  or  i=2igNew range is doubled i.e., 4igNow shunt requiredS=ig4ig−ig30=10ΩThis can be obtained by shunting the earlier shunt of 30 Ωith a new shunt of 15Ω