Expressing A Quantity In Polar Coordinates?

In summary: The Laplacian in polar coordinates is∂2/∂r2 + (1/r) ∂/∂r + (1/r2) ∂2/∂θ2In summary, to express the quantity ∂2/∂x2+∂2/∂y2 in polar coordinates, you need to use the Laplacian operator in polar coordinates, which is ∂2/∂r2 + (1/r) ∂/∂r + (1/r2) ∂2/∂θ2.
  • #1
Xerxesshock2
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Homework Statement


Express the quantity ∂2/∂x2+∂2/∂y2 in polar coordinates.

Homework Equations


x=ρcosφ
y=ρsinφ
ρ=sqrt(x2+y2)

The Attempt at a Solution


This is my first post, so I apologize for any weird looking equations, etc. I know that this is not a difficult problem, but I just cannot figure out exactly how to set it up. I don't know what function to differentiate for x and y... Any guidance would be appreciated. Thank you!
 
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  • #2
Start by determining the first derivatives of x and y with respect to ##\rho## and ##\phi## and then repeat it for the second derivatives of x and y.

and please show your work. We can't help you without you showing your work.

Also try learning latex when entering your symbols for consistency with other posts here at PF.

We quote our expressions with double # front and back: #.#.\rho.#.# (remove the dots to see the rho as a greek letter)

Here's the PF reference:

https://www.physicsforums.com/threads/physics-forums-faq-and-howto.617567/#post-3977517

and here's a more extensive LaTex cheat sheet:

http://users.dickinson.edu/~richesod/latex/latexcheatsheet.pdf
 
Last edited:
  • #3
Xerxesshock2 said:

Homework Statement


Express the quantity ∂2/∂x2+∂2/∂y2 in polar coordinates.

Homework Equations


x=ρcosφ
y=ρsinφ
ρ=sqrt(x2+y2)

The Attempt at a Solution


This is my first post, so I apologize for any weird looking equations, etc. I know that this is not a difficult problem, but I just cannot figure out exactly how to set it up. I don't know what function to differentiate for x and y... Any guidance would be appreciated. Thank you!

2/∂x2+∂2/∂y2 is not a quantity.

It is the Laplacian expressed in cartesian coordinates. (otherwise known as the ∇2 operator)

http://hyperphysics.phy-astr.gsu.edu/hbase/lapl.html
 
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1. What are polar coordinates?

Polar coordinates are a mathematical system used to locate points in a plane. They are represented by a distance from the origin (called the radius) and an angle from a reference line (called the polar axis).

2. How do you convert from Cartesian coordinates to polar coordinates?

To convert from Cartesian coordinates (x,y) to polar coordinates (r,θ), you can use the equations r = √(x² + y²) and θ = tan⁻¹(y/x). This means that the radius is the square root of the sum of the squared x and y coordinates, and the angle is the inverse tangent of the y coordinate divided by the x coordinate.

3. What are the advantages of using polar coordinates?

Polar coordinates are useful for describing circular or symmetric patterns, as well as for simplifying calculations involving complex numbers. They can also be more intuitive and easier to visualize in certain situations.

4. How do you convert from polar coordinates to Cartesian coordinates?

To convert from polar coordinates (r,θ) to Cartesian coordinates (x,y), you can use the equations x = r cos(θ) and y = r sin(θ). This means that the x coordinate is the radius multiplied by the cosine of the angle, and the y coordinate is the radius multiplied by the sine of the angle.

5. What is the difference between polar coordinates and spherical coordinates?

Polar coordinates are a two-dimensional system used to locate points in a plane, while spherical coordinates are a three-dimensional system used to locate points in space. In spherical coordinates, an extra coordinate (called the azimuth) is added to represent the angle in the xy plane, and the angle from the z-axis (called the polar angle) is used instead of the radius.

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