Potential difference from a charged wire with voltmeter

[ehabmozart]

Question about potential difference??

Homework Statement

A very long wire carries a uniform linear charge density λ
Using a voltmeter to measure potential difference, you find that
when one probe of the meter is placed 2.5 cm from the wire and
the other probe is 1cm farther from the wire, the meter reads 575 V
(a) What is λ?

Homework Equations

Va-Vb= λ/2∏ε0 * ln(rb/ra)

The Attempt at a Solution

My first question is what does the voltmeter read? Va-Vb or Vb-Va? ... In this case I assume it is Vb-Va.. So in our attempt it should be -575= λ/2∏ε0 * ln(3.5/2.5) .. But this doesn't yield to the answer... Any thoughts!?

 

[Sunil Simha]

My first question is what does the voltmeter read? Va-Vb or Vb-Va? ... In this case I assume it is Vb-Va.. So in our attempt it should be -575= λ/2∏ε0 * ln(3.5/2.5) .. But this doesn't yield to the answer... Any thoughts!?

The question only says that |V_b-V_a| is 575 V. So you can only find|λ|.