Test Preparation on Current Electricity-III-Physics Test Series IIT JEE-2020

A potentiometer wire is 100 cm long and a constant
potential difference is maintained across it. Two cells are
connected in series first to support one another and then in
opposite direction. The balance points are obtained at 50
cm and 10 cm from the positive end of the wire in the two
cases. The ratio of emf’s is

A galvanometer of resistance 50W is connected to a battery
of 3V along with a resistance of 2950W in series. A full scale
deflection of 30 divisions is obtained in the galvanometer. In
order to reduce this deflection to 20 divisions, the resistance
in series should be