# Homework Help: Work done moving charge near a line of charge

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1. Mar 12, 2016

### Teameister

1. The problem statement, all variables and given/known data
How much work (in J) is required to bring a charge of 2 microC from the point {2*6.8,-7,2*1.1}cm via the point {10,20,1}cm to the point {-3*6.8,3.4,-3*1.1}cm, in a medium with relative permittivity of 3.7, near a line charge along x=6.8 cm, z=1.1 cm, with charge density +329 microC/m? (Hint: what is the sign of the answer? Note that * simply means scalar multiplication)

2. Relevant equations
V= integral (E.dl) yields V=(charge/length)ln(R)/(2pi(relative permittivity)
W=Q(deltaV)

3. The attempt at a solution
I've tried to calculate the voltage at the first point but get a huge number assuming the line of point charges is acting as a cylindrical charge at the first point then same for middle point and last then using W=Q(deltaV).

No success.

Could someone please point me in the right direction.

Do I even need to consider the middle point?

Thank you.

2. Mar 12, 2016

### drvrm

you have three points and a charge to be carried -the possible way is to calculate the potential due to line of charge(a finite distribution)
the way is to break the line distribution in 'small elements' and calculate the resultant field by adding and/ integrating along the full line so that all charges are accounted for and then proceed further.
i do not understand how you write the expression for potential and what is R?

3. Mar 13, 2016

### vela

Staff Emeritus