Finding a function in conservative field

In summary, the conversation discusses finding a non-zero function h(x) that makes a given field conservative. The approach involves using the curlF=0 equation and the product rule to find the derivatives and eventually solving for h(x). The final solution is that h(x) must be equal to its derivative, making it a constant function.
  • #1
greenfrog
3
0

Homework Statement



Find the non-zero function h(x) for which:

field F(x,y) = h(x) [xsiny + ycosy] i + h(x) [xcosy - ysiny] j

is conservative.

The Attempt at a Solution



curlF=0
d/dx [h(x) [xcosy - ysiny] ] - d/dy [h(x) [xsiny + y cos y] ] = 0

xcosy = ysiny ?

I have no idea!
 
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  • #2
greenfrog said:
curlF=0
d/dx [h(x) [xcosy - ysiny] ] - d/dy [h(x) [xsiny + y cos y] ] = 0

That is only the z-component of curlF...all 3 components will have to be zero.

You will need to use the product rule when computing the derivatives...
 
  • #3
Thanks for the reply but I'm not sure I understand... do u mean this? ...

curlF= {d/dy[0]-d/dz[ h(x)[xcosy - ysiny]]} - {d/dx[0]-d/dz[ h(x)[xsiny + ysiny]]} + {d/dx[ h(x)[xcosy - ysiny]] - d/dy[ h(x)[xsiny + ycosy]]}

= 0 - 0 + d/dx[ h(x)[xcosy - ysiny]] - d/dy[ h(x)[xsiny + ycosy]]}

= [ h`(x)xcosy + h(x)cosy - h`(x)ysiny] - [ h(x)xcosy - h(x)ysiny + h(x)cosy ]

= h`(x)xcosy + h(x)cosy - h`(x)ysiny - h(x)xcosy + h(x)ysiny - h(x)cosy

= h`(x)xcosy - h`(x)ysiny - h(x)xcosy + h(x)ysiny

= xcosy [h`(x) - h(x)] + ysiny [h(x) - h`(x)]

= xcosy [h`(x) - h(x)] - ysiny [h`(x) - h(x)]

= [h`(x) - h(x)] [xcosy - ysiny] = 0

as h(x) is a non-zero vector then xcosy - ysiny = 0

xcosy = ysiny


And the no matter what I do I can't seem to get h(x).
 
  • #4
greenfrog said:
= [h`(x) - h(x)] [xcosy - ysiny] = 0

as h(x) is a non-zero vector then xcosy - ysiny = 0

xcosy = ysiny

No, you can't pick and choose x and y values such that xcosy = ysin y , you are looking to choose an h(x) that makes [h`(x) - h(x)] [xcosy - ysiny] = 0 for all x and y...The only way that can happen is if
[h`(x) - h(x)]=0...right? What kind of non-trivial function accomplishes that?:wink:
 
  • #5
thanks! i got it.
 

Related to Finding a function in conservative field

1. What is a conservative field?

A conservative field is a type of vector field in which the path taken by a particle from one point to another does not affect the work done by the field on the particle. This means that the total energy of the particle remains constant regardless of the path taken.

2. How do you determine if a field is conservative?

One way to determine if a field is conservative is by checking if it satisfies the curl condition. If the curl of the field is equal to zero, then the field is conservative. Another method is by checking if the field is derived from a scalar potential function.

3. What is a scalar potential function?

A scalar potential function is a mathematical function that is used to describe a conservative field. It assigns a scalar value to each point in the field, which represents the potential energy of a particle at that point. The gradient of this function gives the field's vector at any given point.

4. Why is it important to find a function in a conservative field?

Finding a function in a conservative field can help in understanding the behavior of the field and predicting the motion of particles within it. It also allows for the calculation of work and potential energy in the field, which can have practical applications in fields such as physics and engineering.

5. What are some real-life examples of conservative fields?

Some common examples of conservative fields include gravitational fields, electric fields, and magnetic fields. These fields exhibit conservative behavior, where the work done on a particle depends only on the initial and final positions, and not on the path taken. Other examples include fluid flow, stress and strain fields, and temperature fields.

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