In an experiment with a potentiometer, VB = 10V. R is adjusted to be 50Ω (figure). A student wanting to measure the voltage E1 of a battery (approx. 8V) finds no null point possible. He then diminishes R to 10Ω and is able to locate the null point on the last (4th) segment of the potentiometer. Find the resistance of the potentiometer wire and potential drop per unit length across the wire in the second case.