In an experiment with a potentiometer `V_B=10 V`, R is adjusted to be `50 Omega` as shown in figure. A student wanting to measure voltage `E_1` of a battery (approx. 8 V) finds no null point possible. He then diminishes R to `10 Omega` and is able to locate the null point on the last (4th) segment of potentiometer.Find the resistance of the potentiometer wire and potential drop per unit length across the wire in the second case.