Finding limits of integral in spherical coordinates

In summary, the conversation discusses converting an integral to spherical coordinates and determining the limits for the integration. The shape being integrated is a spherical or elliptical shape, with limits for r going from 0 to 2, theta going from 0 to pi/2, and phi going from 0 to pi. The conversation also includes a discussion on the shape's minimum and maximum values for x, y, and z.
  • #1
uzman1243
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Homework Statement


The question asks me to convert the following integral to spherical coordinates and to solve it
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Homework Equations

The Attempt at a Solution


just the notations θ = theta and ∅= phi

dx dy dz = r2 sinθ dr dθ d∅
r2 sinθ being the jacobian

and eventually solving gets me
∫ ∫ ∫ r4 *sin2θ * sin∅ dr dθ d∅

How do I find the limits now?
 

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  • #2
Use the limits in the Cartesian system to figure out the enclosed shape. What is the minimum and maximum value of z? Those of y and x?
 
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  • #3
ehild said:
Use the limits in the Cartesian system to figure out the enclosed shape. What is the minimum and maximum value of z? Those of y and x?

x goes from -2 to 2
y goes from 0 to √4-x2 circle with radius 2
z from 0 to √4-x2-y2 sphere with with radius 2

so I am guessing
r goes from 0 to 2
∅ and θ from 0 to 2π
 
  • #4
Are you sure in 2pi?
 
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  • #5
ehild said:
Are you sure in 2pi?
ok so ∅ goes from 0 to 2pi as it is some sort of sphere/ elipse. correct?
 
  • #6
See picture. Yes, the shape is spherical, but you have to integrate with respect to y from zero to some positive value, goes it round a whole circle?

intshape.JPG
 
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  • #7
ehild said:
See picture. Yes, the shape is spherical, but you have to integrate with respect to y from zero to some positive value, goes it round a whole circle?

View attachment 82540
ahhh so θ goes from 0 to pi
∅ goes from 0 to 2pi
and r goes from 0 to 2
correct?
 
  • #8
Those were the limit for the whole sphere. But the integration does not go for negative z values, neither for negative y values.
 
  • #9
ehild said:
Those were the limit for the whole sphere. But the integration does not go for negative z values, neither for negative y values.
r goes from 0 to 2
theta goes from 0 to pi/2
phi goes from 0 to pi
correct?
 
Last edited:
  • #10
Looks good.
 
  • #11
uzman1243 said:
r goes from 0 to 2
theta goes from 0 to pi/2
phi goes from 0 to pi
correct?
Yes. :smile:
 
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FAQ: Finding limits of integral in spherical coordinates

What are spherical coordinates?

Spherical coordinates are a system of coordinates used to describe points in three-dimensional space. They consist of a radial distance from the origin, an azimuth angle measured from a reference direction, and an elevation angle measured from the reference plane.

Why do we use spherical coordinates?

Spherical coordinates are useful when working with three-dimensional problems that involve spherical symmetry. They are also commonly used in physics and engineering for describing the position and movement of objects in three-dimensional space.

How do you convert from spherical coordinates to Cartesian coordinates?

To convert from spherical coordinates (r, θ, φ) to Cartesian coordinates (x, y, z), use the following equations:
x = r sinφ cosθ
y = r sinφ sinθ
z = r cosφ
where r is the radial distance, θ is the azimuth angle, and φ is the elevation angle.

What is the process for finding limits of integrals in spherical coordinates?

The limits of an integral in spherical coordinates are determined by the shape and boundaries of the region being integrated. To find the limits, you must first determine the range of the radial distance, azimuth angle, and elevation angle within the region. Then, set up the integral using these limits and integrate according to the appropriate formula.

What are some common mistakes when finding limits of integrals in spherical coordinates?

Some common mistakes when finding limits of integrals in spherical coordinates include:
- Forgetting to convert the limits to the appropriate units (e.g. converting radians to degrees)
- Using the wrong integration formula for the given region
- Not considering the symmetry of the region and including unnecessary limits
- Confusing the order of the limits, which can result in incorrect answers.

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