Question about potential difference?

AI Thread Summary
The discussion revolves around calculating the linear charge density (λ) of a long wire based on a measured potential difference of 575 V between two points at varying distances from the wire. The equation used is Va-Vb= λ/2∏ε0 * ln(rb/ra), where the user is uncertain about the correct interpretation of the voltmeter reading. It is clarified that the absolute value of the potential difference, |Vb-Va|, is given as 575 V, allowing for the determination of |λ| rather than λ itself. The user is encouraged to proceed with this understanding to solve for the charge density.
ehabmozart
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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!?
 
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ehabmozart said:
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 |Vb-Va| is 575 V. So you can only find|λ|.
 

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