Electrostatics and integration

Find V A V B \displaystyle{V_{A}-V_{B}} in volts.

Where V P V_{P} is electric potential at point P. If A = ( 0 , 0 , 0 ) A=(0,0,0) and B = ( 2 , 2 , 2 ) B=(2,2,2) and electric field E = 6 x y i ^ + 3 ( x 2 y 2 ) j ^ \overrightarrow { E } =6xy \hat { i } +3(x^2-y^2)\hat { j }

Also see my set


The answer is 16.

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4 solutions

Jafar Badour
Mar 23, 2015

we multiply by (idx+jdy+kdz) then we partial integrate from 0 to 2 on x axis and from 0 to 2 on y axis

Deepanshu Gupta
Mar 21, 2015

Too easy: [trick required is]

6 x y d x + 3 x 2 d y = 3 d ( x 2 y ) \displaystyle{6xydx+3x^2dy=3d(x^2y)}

@Tanishq Varshney Please do not use text in the latex code , and don't randomly use Huge words . It looks ugly and difficult to read. I have edited several of your questions . It will be better and helpful for us if you take care it in future.
Thanks .

next time for sure i will take care. i do so , becoz the question will occupy more space on the questions area and it would'nt go unnoticed . for example this problem occupy less space so it is unnoticed to many.

Tanishq Varshney - 6 years, 2 months ago

i believe that there is no need of doing 6 x y d x + 3 x 2 d y = 3 d ( x 2 y ) \displaystyle{6xydx+3x^2dy=3d(x^2y)} there's a more easy way to do it!! just integrate E with (idx+jdy+kdz) to get 6 x y d x + 3 ( x 2 y 2 ) d y ) \displaystyle{6xydx+3(x^2-y^2)dy)} and put x=y to get 6 x 2 d x ) \displaystyle{6x^2dx)} and integrate with limits from 0 to 2!!

This question can be solved without a complex integral of the sorts given below.

Just think about the journey from ( 0 , 0 , 0 ) (0,0,0) to ( 2 , 2 , 2 ) (2,2,2) in three steps:

  • Moving along X a x i s X-axis from ( 0 , 0 , 0 ) (0,0,0) to ( 2 , 0 , 0 ) (2,0,0) .

  • Moving from ( 2 , 0 , 0 ) (2,0,0) to ( 2 , 2 , 0 ) (2,2,0) along the X Y X-Y plane.

  • Moving from ( 2 , 2 , 0 ) (2,2,0) to ( 2 , 2 , 2 ) (2,2,2) through space.

Now, for the first step, the work will be done only but the force along X a x i s X-axis , but since force along this axis is given by 6 x y 6xy and y = 0 y=0 for the X a x i s X-axis , hence the force is zero, or in other words, no work is done.

For the second step, the work is done only by the force in the upward direction, i.e. 3 ( x 2 y 2 ) 3({x}^{2}-{y}^{2}) . Since, for this step, the X-coordinate is fixed at x = 2 x=2 , the work is done by the force 12 3 y 2 12-3{y}^{2} , which can be written as

0 2 ( 12 3 y 2 ) d y \int _{ 0 }^{ 2 }{ (12-3{ y }^{ 2 }) } dy

which when simplified gives 16 V 16 V of potential difference.

For the third step, there is again no force acting along the Z a x i s Z-axis and hence no work is done yet again.

Therefore, total potential developed is only due to the second step i.e. 16 J 16J

Note

You can choose any path. Since, potential difference is a state function, choosing the path I suggested simplifies the scenario.

Upvoted! Thanks for not forgetting to check if the field is conservative :)

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