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Triple Integrals In Spherical Coordinates

In the previous section we looked at doing integrals in terms of cylindrical coordinates and we now need to take a quick look at doing integrals in terms of spherical coordinates.
First, we need to recall just how spherical coordinates are defined. The following sketch shows the relationship between the Cartesian and spherical coordinate systems.
Triple Integrals In Spherical Coordinates

Here are the conversion formulas for spherical coordinates.
Triple Integrals In Spherical Coordinates
Triple Integrals In Spherical Coordinates
We also have the following restrictions on the coordinates.
Triple Integrals In Spherical Coordinates
For our integrals we are going to restrict E down to a spherical wedge. This will mean that we are going to take ranges for the variables as follows,
a ≤ ρ ≤ b, α ≤ θ ≤ β, δ ≤ φ ≤ γ
Here is a quick sketch of a spherical wedge in which the lower limit for both ρ and φ are zero for reference purposes. Most of the wedges we'll be working with will fit into this pattern.
Triple Integrals In Spherical Coordinates
From this sketch we can see that E is nothing more than the intersection of a sphere and a cone and generally will represent a shape that is reminiscent of an ice cream cone.
In the next section we will show that
dV=ρ2sinφdρdθdφ
Therefore, the integral will become,
Triple Integrals In Spherical Coordinates
This looks bad but given that the limits are all constants the integrals here tend to not be too bad.
Example 1 Evaluate Triple Integrals In Spherical CoordinatesEE is the upper half of the sphere Triple Integrals In Spherical Coordinates
Solution: Since we are taking the upper half of the sphere the limits for the variables are, 
Triple Integrals In Spherical Coordinates
The integral is then, 
Triple Integrals In Spherical Coordinates
Example 2 Evaluate Triple Integrals In Spherical Coordinateswhere E is above x2 + y2 = 4 , inside the cone (pointing upward) that makes an angle of π/3 with the negative z-axis and has x≤0
Solution : First, we need to take care of the limits. The region E is basically an upside down ice cream cone that has been cut in half so that only the portion with x ≤ 0 remains. Therefore, because we are inside a portion of a sphere of radius 2 we must have,
0ρ2 
For φ we need to be careful. The problem statement says that the cone makes an angle of π/3 with the negative z -axis. However, remember that φ is measured from the positive z -axis. Therefore, the first angle, as measured from the positive z -axis, that will "start" the cone will be φ = 2 π/3 and it goes to the negative z -axis. Therefore, we get the following limits for φ 
2π/3φπ
Finally, for the θ we can use the fact that we are also told that x ≤ 0 . This means we are to the left of the y-axis and so the range of θ must be,
π/2 θ 3π/2
Now that we have the limits we can evaluate the integral.Triple Integrals In Spherical Coordinates
Triple Integrals In Spherical Coordinates
Triple Integrals In Spherical Coordinates
Example 3 Convert Triple Integrals In Spherical Coordinates into spherical coordinates.
Solution: Let's first write down the limits for the variables.

Triple Integrals In Spherical Coordinates 
The range for x tells us that we have a portion of the right half of a disk of radius 3 centered at the origin. Since we are restricting y 's to positive values it looks like we will have the quarter disk in the first quadrant. Therefore, since D is in the first quadrant the region, E , must be in the first octant and this in turn tells us that we have the following range for θ (since this is the angle around the z -axis).
0θ π/2
Now, let's see what the range for z tells us. The lower bound,Triple Integrals In Spherical Coordinates , is the upper half of a cone. At this point we don't need this quite yet, but we will later. The upper bound,Triple Integrals In Spherical Coordinates , is the upper half of the sphere,
Triple Integrals In Spherical Coordinates
and so from this we now have the following range for ρ
Triple Integrals In Spherical Coordinates
Now all that we need is the range for φ . There are two ways to get this. One is from where the cone and the sphere intersect. Plugging in the equation for the cone into the sphere gives,
Triple Integrals In Spherical Coordinates
Note that we can assume z is positive here since we know that we have the upper half of the cone and/or sphere. Finally, plug this into the conversion for z and take advantage of the fact that we know that ρ = 3 √ 2 since we are intersecting on the sphere. This gives,
Triple Integrals In Spherical Coordinates    Triple Integrals In Spherical Coordinates

So, it looks like we have the following range, Triple Integrals In Spherical Coordinates
The other way to get this range is from the cone by itself. By first converting the equation into cylindrical coordinates and then into spherical coordinates we get the following
Triple Integrals In Spherical Coordinates
So, recalling that ρ2= x+ y+ z2, the integral is then,
Triple Integrals In Spherical Coordinates

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FAQs on Triple Integrals In Spherical Coordinates

1. What are spherical coordinates and how are they used in triple integrals?
Ans. Spherical coordinates are a coordinate system that is used to describe points in three-dimensional space. They consist of three parameters: radius (ρ), inclination (θ), and azimuth (φ). In triple integrals, spherical coordinates are used to simplify the integration process when the region of integration has spherical symmetry. The conversion from rectangular coordinates to spherical coordinates involves using trigonometric functions and can be done using the following formulas: x = ρ * sin(θ) * cos(φ) y = ρ * sin(θ) * sin(φ) z = ρ * cos(θ)
2. How do you set up a triple integral in spherical coordinates?
Ans. To set up a triple integral in spherical coordinates, you need to express the integrand and the region of integration in terms of spherical coordinates. The triple integral takes the form ∭f(ρ, θ, φ)ρ²sin(θ)dρdθdφ, where f(ρ, θ, φ) is the integrand, ρ is the radius, θ is the inclination angle, and φ is the azimuth angle. The region of integration can be described using appropriate limits for ρ, θ, and φ, depending on the shape and size of the region.
3. What are the advantages of using spherical coordinates in triple integrals?
Ans. Spherical coordinates offer several advantages in the context of triple integrals. Firstly, they are particularly useful when dealing with regions of integration that exhibit spherical symmetry, as the equations become simpler and more elegant. Secondly, spherical coordinates provide a natural way to describe points in three-dimensional space, especially in scenarios involving spherical objects or systems. Finally, spherical coordinates can sometimes simplify the calculation of triple integrals by reducing the complexity of the integrand or allowing for easier selection of appropriate limits of integration.
4. What are some common applications of triple integrals in spherical coordinates?
Ans. Triple integrals in spherical coordinates have numerous applications in mathematics and physics. Some common examples include calculating the volume of a solid with spherical symmetry, finding the center of mass of a three-dimensional object, determining the total mass of a three-dimensional object with varying density, calculating electric flux through a closed surface, and solving problems involving the gravitational potential of a spherical mass distribution.
5. How can I convert a given triple integral from rectangular coordinates to spherical coordinates?
Ans. To convert a given triple integral from rectangular coordinates (x, y, z) to spherical coordinates (ρ, θ, φ), follow these steps: 1. Express x, y, and z in terms of ρ, θ, and φ using the formulas x = ρ * sin(θ) * cos(φ), y = ρ * sin(θ) * sin(φ), and z = ρ * cos(θ). 2. Determine the limits of integration for ρ, θ, and φ based on the region of integration in rectangular coordinates. 3. Calculate the Jacobian determinant of the coordinate transformation, which is ρ²sin(θ). 4. Rewrite the integrand in terms of ρ, θ, and φ. 5. Replace dV (the volume element in rectangular coordinates) with ρ²sin(θ)dρdθdφ. 6. Set up the triple integral using the new variables and limits of integration.
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