Laplacian of polar coordinates

In summary, the conversation discusses a problem with calculating the Laplacian in polar coordinates. The attached solution is questioned for including unit vectors and their derivatives, which are not necessary for the scalar operator. The suggested method is to use the chain rule and perform the calculations for x and y separately before adding the results. This method may involve tedious algebra but is necessary to fully understand the concept.
  • #1
davon806
148
1

Homework Statement


I am trying to calculate the laplacian in polar coordinates but I failed.Please see the attached

Homework Equations




The Attempt at a Solution


My solution to this was uploaded in the attached.I was wondering what's wrong with the purple brackets since they shouldn't exist( If you sum A,B,C and D up). Thanks
 

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  • #2
I don't think you should be messing with unit vectors and their derivatives. The Laplacian is a scalar operator. It looks like you are doing it in two dimensions. Start with $$\nabla ^2=\frac{\partial^2}{\partial x^2} + \frac{\partial^2}{\partial y^2}$$
Observe that according to the chain rule
$$\frac{\partial}{\partial x}=\frac{\partial r}{\partial x}\frac{\partial}{\partial r}+\frac{\partial \theta}{\partial x}\frac{\partial}{\partial \theta}$$
and one more time for the second partial derivative. Repeat with y and then add the two results.

This is the "brute force" method and involves tedious algebra. It is the kind of thing that one has to do once in one's life to satisfy oneself that one can do it. :smile:
 
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Related to Laplacian of polar coordinates

What is the Laplacian of polar coordinates?

The Laplacian of polar coordinates is a mathematical operator used in vector calculus to describe the rate of change of a function in terms of its second derivatives with respect to polar coordinates. It is denoted by the symbol ∇² and is also known as the Laplace operator.

How is the Laplacian of polar coordinates calculated?

The Laplacian of polar coordinates is calculated using the following formula: ∇² = (1/r) ∂/∂r (r ∂/∂r) + (1/r²) ∂²/∂θ², where r is the radial coordinate and θ is the angular coordinate. This formula can be derived from the Cartesian form of the Laplacian using the chain rule.

What is the physical interpretation of the Laplacian of polar coordinates?

The Laplacian of polar coordinates can be interpreted as a measure of the curvature of a function in polar coordinates. It describes how the function changes with respect to both the radial distance and the angle at which it is measured.

What are the applications of the Laplacian of polar coordinates?

The Laplacian of polar coordinates has many applications in physics and engineering, such as in the study of electromagnetic fields, fluid dynamics, and heat transfer. It is also used in image processing and computer graphics to enhance and manipulate images.

How does the Laplacian of polar coordinates relate to the Laplace equation?

The Laplacian of polar coordinates is closely related to the Laplace equation, which is a partial differential equation that describes the behavior of a scalar function. In polar coordinates, the Laplacian of a function is equal to zero if the function satisfies the Laplace equation.

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