A galvanometer of resistance 100  gives full scale deflection at 10 mA current. What should be the value of shunt so that it can measure a current of 100 mA?

Answer 1

I assume that is 100 ohms.
so with the shunt, the original galvanometer will have 10mA and the shunt 90 mA at full scale. So the shunt resistance must be 1/9 the galvanometer to carry 9 times the current.
Resistance shunt=100/9=11.1 ohms

check:
original meter full scale has 10mA, or 1 volt (IR=.01*100=1volt)
Now at 1volts, with the shunt, total current is V*conductance=
=1*(.01+.09)= 100ma, and the amount going thru the meter is 10mA, a full scale reading.