Recast a given vector field F in cylindrical coordinates

In summary: I got (2rcos2(θ)eθ+ 2rsin2(θ)er) as my final answer.In summary, the conversation discusses the calculation of F(x,y,z) = xzi and its curl in both Cartesian and cylindrical coordinates. The unit vector ## \hat{i} ## is also converted to cylindrical coordinates and used in the calculation. The final answer, accounting for a mistake in the original response, is found to be (2rcos2(θ)eθ+ 2rsin2(θ)er).
  • #1
Bestphysics112
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Homework Statement


F(x,y,z) = xzi

Homework Equations


N/A

The Attempt at a Solution


I just said that x = rcos(θ) so F(r,θ,z) = rcos(θ)z. Is this correct? Beaucse I am also asked to find curl of F in Cartesian coordinates and compare to curl of F in cylindrical coordinates. For Curl of F in cylindrical coordinates I obtained rcos(θ)eθ+sin(θ)zez. This doesn't look anything like the curl found in Cartesian coordinates. Where am i going wrong?
 
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The unit vector ## \hat{i} ## also needs to be put in cylindrical coordinates. ## \hat{i}=cos(\theta) \hat{a}_r -sin(\theta) \hat{a}_{\theta} ## if I computed it correctly. Once you do that, you should get agreement when you do the curl operation in cylindrical coordinates. ## \\ ## Editing: Yes, I computed it, and got agreement. I'd be happy to check the answer for you that you get.
 
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  • #3
Charles Link said:
The unit vector ## \hat{i} ## also needs to be put in cylindrical coordinates. ## \hat{i}=cos(\theta) \hat{a}_r -sin(\theta) \hat{a}_{\theta} ## if I computed it correctly. Once you do that, you should get agreement when you do the curl operation in cylindrical coordinates. ## \\ ## Editing: Yes, I computed it, and got agreement. I'd be happy to check the answer for you that you get.
Hello! Sorry I just saw this reply. As an answer, I got (rcos(θ)sin(θ)er +rcos2(θ)eθ +(2cos(θ)sin(θ)z+ 2sin(θ)cos(θ)z)ez

Is this answer correct?

Edit- Yes! I figured out my mistake and I got an equivalent answer. Thank you for the help Charles
 
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  • #4
Bestphysics112 said:
Hello! Sorry I just saw this reply. As an answer, I got (rcos(θ)sin(θ)er +rcos2(θ)eθ +(2cos(θ)sin(θ)z+ 2sin(θ)cos(θ)z)ez

Is this answer correct?

Edit- Yes! I figured out my mistake and I got an equivalent answer. Thank you for the help Charles
Please check your ## e_z ## term. The first term gets a minus sign so that the ## e_z ## term is zero. Also what did you get in Cartesian coordinates for the curl? The two should agree and I think they do if the ## e_z ## term is zero.
 
  • #5
Charles Link said:
Please check your ## e_z ## term. The first term gets a minus sign so that the ## e_z ## term is zero. Also what did you get in Cartesian coordinates for the curl? The two should agree and I think they do if the ## e_z ## term is zero.
I don't have my homework with me, but I forgot to edit my post with the answer I got. The ez terms canceled
 
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1. What is the purpose of recasting a vector field in cylindrical coordinates?

Recasting a vector field in cylindrical coordinates allows for a more intuitive understanding and visualization of the field. It also simplifies calculations and makes it easier to solve certain problems.

2. How do you convert a vector field from Cartesian coordinates to cylindrical coordinates?

To convert a vector field from Cartesian coordinates to cylindrical coordinates, you need to use the following equations:
r = √(x2 + y2)
θ = tan-1(y/x)
z = z
Once you have these values, you can rewrite the vector field in terms of r, θ, and z.

3. What are the advantages of using cylindrical coordinates over Cartesian coordinates?

Cylindrical coordinates are especially useful when dealing with cylindrical objects or problems with cylindrical symmetry. They allow for simpler and more efficient calculations and can often provide a more intuitive understanding of the vector field.

4. Can any vector field be recast in cylindrical coordinates?

Yes, any vector field can be recast in cylindrical coordinates as long as the equations and transformations are applied correctly. However, it may not always be the most practical or useful approach depending on the problem at hand.

5. Are there any limitations to using cylindrical coordinates for vector fields?

One limitation of using cylindrical coordinates is that they are not suitable for all types of vector fields. For example, if the field has a lot of z-component variation, it may be better to keep it in Cartesian coordinates. Additionally, the equations and transformations for cylindrical coordinates can become more complex for higher dimensions, making it more difficult to recast the vector field.

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