Cylinderical reigon and potential difference

[fight_club_alum]

Homework Statement

The charge of density 3.0 μC/m fills a long cylindrical region having a 2.0-cm radius. If point A is 1.0 cm from the symmetry-axis and point B is 2.0 cm from the symmetry-axis, what is the potential difference VA – VB?
a . –25 mV

b. +42 mV

c. –42 mV

d. +25 mV

e. +20 mV <- answer

Homework Equations

- integral( E . dr) = delta V

The Attempt at a Solution

EA = Q/eo
E(2*pi*r*h) = lambda * h / eo
E = (lambda) /( eo * 2 * pi * r)
-integral(lambda/eo* 2 * r * pi) dr from 0.01 ro 0.02 <--- gives me the wrong answer

 

[BvU]

yes. did you notice A is 'inside' the charge ?