Chapter 5: Problem 38
Compute \(\iint_{S} \mathbf{F} \cdot \mathbf{N} d S\), where \(\mathbf{F}(x, y, z)=2 y z \mathbf{i}+\left(\tan ^{-1} x z\right) \mathbf{j}+e^{x y} \mathbf{k}\) and \(\mathbf{N}\) is an outward normal vector \(S\), where S is the surface of sphere \(x^{2}+y^{2}+z^{2}=1\).
Short Answer
Expert verified
The surface integral is 0.
Step by step solution
01
Understand the Surface
The surface S is defined as the sphere given by the equation \( x^2 + y^2 + z^2 = 1 \). We identify this as a closed surface, specifically the unit sphere.
02
Vector Field Analysis
Given vector field is \( \mathbf{F}(x, y, z) = 2yz \mathbf{i} + \tan^{-1}(xz) \mathbf{j} + e^{xy} \mathbf{k} \). This vector field needs to be integrated over the surface of the sphere.
03
Apply Divergence Theorem
According to the Divergence Theorem, for a closed surface \( S \), \( \iint_{S} \mathbf{F} \cdot \mathbf{N} \, d S = \iiint_{V} abla \cdot \mathbf{F} \, dV \) where \( V \) is the volume inside \( S \). Calculate \( abla \cdot \mathbf{F} \).
04
Compute the Divergence
The divergence \( abla \cdot \mathbf{F} \) is the dot product of the nabla operator and \( \mathbf{F} \): \( abla \cdot \mathbf{F} = \frac{\partial}{\partial x}(2yz) + \frac{\partial}{\partial y}(\tan^{-1}(xz)) + \frac{\partial}{\partial z}(e^{xy}) \).
05
Evaluate Divergence Terms Individually
Calculate each term separately:- \( \frac{\partial}{\partial x}(2yz) = 0 \).- \( \frac{\partial}{\partial y}(\tan^{-1}(xz)) = 0 \).- \( \frac{\partial}{\partial z}(e^{xy}) = 0 \).Thus, \( abla \cdot \mathbf{F} = 0 \).
06
Integrate Divergence Over Volume
Since \( abla \cdot \mathbf{F} = 0 \), the volume integral \( \iiint_{V} 0 \, dV = 0 \). This implies \( \iint_{S} \mathbf{F} \cdot \mathbf{N} \, d S = 0 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Closed Surface
A closed surface is a geometric shell that completely encloses a volume. It has no openings or boundaries. Think of it as similar to a balloon, which neatly encloses the air inside it.
One important characteristic of a closed surface is that what goes in must come out, influencing field calculations and flow analysis.
One important characteristic of a closed surface is that what goes in must come out, influencing field calculations and flow analysis.
- Closed surfaces include spheres, cubes, and any shape you can imagine that fully encapsulates a space.
- When dealing with a closed surface, we can make use of the Divergence Theorem, which connects the surface integral of a vector field over a closed surface with a corresponding volume integral inside the surface.
Vector Field
A vector field assigns a vector to every point in space, much like assigning a direction and strength of a flowing river at each point along its path.
In mathematical terms, a vector field is represented by a function like \( \mathbf{F}(x, y, z) \). This function assigns vectors based on the values of \( x, y, \) and \( z \).
In mathematical terms, a vector field is represented by a function like \( \mathbf{F}(x, y, z) \). This function assigns vectors based on the values of \( x, y, \) and \( z \).
- For instance, in our exercise, we have the vector field \( \mathbf{F}(x, y, z) = 2yz \mathbf{i} + \tan^{-1}(xz) \mathbf{j} + e^{xy} \mathbf{k} \).
- This equation specifies a different vector for every point \( (x, y, z) \) in three-dimensional space.
Unit Sphere
A unit sphere is a sphere with a radius of 1. It's a simple, perfectly round shape fundamental in geometry and is used frequently in mathematical exercises as an ideal closed surface.
The equation \( x^2 + y^2 + z^2 = 1 \) defines this unit sphere. Any point \((x, y, z)\) that satisfies this equation is on the surface of the unit sphere.
The equation \( x^2 + y^2 + z^2 = 1 \) defines this unit sphere. Any point \((x, y, z)\) that satisfies this equation is on the surface of the unit sphere.
- The unit sphere is particularly convenient for calculations due to its symmetry and simplicity.
- It is utilized in problems involving integration because it makes applying the Divergence Theorem straightforward.