In an experiment with a potentiometer, R is adjusted to be (Figure). A student wanting to measure voltage E1 of a battery (approx. 8V) finds no null point possible. He then diminishes R to 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.
Req=50+R
Veq=10V
The potential difference across the potentiometer
V'<8
R'<200
R'>40
At balance point:
R'>-160
As R’ can only be positive, R'>160
k>2 V/m
As balance, point isn’t at 3m