A potentiometer wire PQ of 1m length is connected to a standard cell $$E_1$$. Another cell $$E_2$$ of emf 1.02 V is connected with a resistance 'r' and switch S (as shown in figure). With switch S open, the null position is obtained at a distance of 49 cm from Q. The potential gradient in the potentiometer wire is:

A

0.02 V/cm

B

0.01 V/cm

C

0.03 V/cm

D

0.04 V/cm