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Gradient fields Find the gradient field \(\mathbf{F}=\nabla \varphi\) for the following potential functions \(\varphi.\) $$\varphi(x, y, z)=e^{-z} \sin (x+y)$$

Short Answer

Expert verified
Question: Find the gradient field 饾懎 for the potential function 饾湋(x, y, z) = e^(-z) sin(x + y). Answer: The gradient field 饾懎 for the given potential function 饾湋(x, y, z) is: $$\mathbf{F} = e^{-z} \cos (x+y) \mathbf{i} + e^{-z} \cos (x+y) \mathbf{j} - e^{-z} \sin (x+y) \mathbf{k}$$

Step by step solution

01

Calculate the partial derivatives

First, we will find the partial derivatives of the potential function with respect to each of the variables x, y, and z. Given potential function \(\varphi(x, y, z)=e^{-z} \sin (x+y)\), let's evaluate the partial derivatives: $$\frac{\partial \varphi}{\partial x} = e^{-z} \cos (x+y)$$ $$\frac{\partial \varphi}{\partial y} = e^{-z} \cos (x+y)$$ $$\frac{\partial \varphi}{\partial z} = -e^{-z} \sin (x+y)$$
02

Construct the gradient field vector

Now that we have found the partial derivatives, let's represent the gradient field vector 饾懎, which is given by: $$\mathbf{F}=\frac{\partial \varphi}{\partial x}\mathbf{i}+\frac{\partial \varphi}{\partial y}\mathbf{j}+\frac{\partial \varphi}{\partial z}\mathbf{k}$$ Substitute the obtained partial derivatives to get the gradient field vector: $$\mathbf{F}= e^{-z} \cos (x+y) \mathbf{i} + e^{-z} \cos (x+y) \mathbf{j} -e^{-z} \sin (x+y) \mathbf{k}$$ Therefore, the gradient field 饾懎 for the given potential function 饾湋(x, y, z) is: $$\mathbf{F} = e^{-z} \cos (x+y) \mathbf{i} + e^{-z} \cos (x+y) \mathbf{j} - e^{-z} \sin (x+y) \mathbf{k}$$

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Partial Derivatives
The concept of partial derivatives extends the idea of differentiation to functions with multiple variables. When working with a multivariable function like \( \varphi(x, y, z) \), we are interested in how this function changes as each individual variable changes, while keeping the other variables constant. Here, we calculated the partial derivatives of the potential function \( \varphi(x, y, z)=e^{-z} \sin (x+y) \):
  • \( \frac{\partial \varphi}{\partial x} = e^{-z} \cos (x+y) \), which tells us how \( \varphi \) changes as \( x \) changes, with \( y \) and \( z \) held constant.
  • \( \frac{\partial \varphi}{\partial y} = e^{-z} \cos (x+y) \), showing the change in \( \varphi \) with respect to \( y \).
  • \( \frac{\partial \varphi}{\partial z} = -e^{-z} \sin (x+y) \), demonstrating the sensitivity of \( \varphi \) as \( z \) changes.
In essence, each partial derivative is like taking a slice of the function picture, focusing on the specified axis and observing how the function behaves as you slide along that axis.
Potential Function
A potential function, like \( \varphi(x, y, z)=e^{-z} \sin (x+y) \), serves as a foundational component in fields such as physics and vector calculus. This function plays a critical role in defining a gradient field, which describes various types of physical phenomena. These include electromagnetic fields, gravitational fields, and fluid flow.
In our context, the potential function is used to compute the gradient, which is a vector field. The gradient vector field \( \mathbf{F} = abla \varphi \) can be thought of as pointing in the direction of the greatest rate of increase of the potential function.
Understanding potential functions helps in visualizing and modeling real-world situations where forces or energies in space need to be considered. The transition from a scalar potential function to a vector field helps make these theoretical concepts applicable to practical examples.
Vector Calculus
Vector calculus is a powerful mathematical tool used to study vector fields and scalar fields. It combines techniques from traditional calculus and applies them to multidimensional arrays of numbers. One of the most important operations in vector calculus is deriving the gradient of a scalar function.
  • In the step-by-step solution, we constructed a gradient field \( \mathbf{F} \) using the potential function \( \varphi(x, y, z) \).
  • The gradient \( \mathbf{F} = e^{-z} \cos (x+y) \mathbf{i} + e^{-z} \cos (x+y) \mathbf{j} - e^{-z} \sin (x+y) \mathbf{k} \) illustrates how the gradient operation "transforms" \( \varphi \) from a scalar to a vector field that provides direction and rate information.
Vector calculus is not only about solving mathematical equations but is essential in fields like fluid dynamics, electromagnetism, and the analytical study of systems with multiple changing variables. By understanding these concepts, students gain insights into how mathematical models can tackle complex real-world problems.

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Most popular questions from this chapter

Consider the radial fields \(\mathbf{F}=\frac{\langle x, y, z\rangle}{\left(x^{2}+y^{2}+z^{2}\right)^{p / 2}}=\frac{\mathbf{r}}{|\mathbf{r}|^{p}},\) where \(p\) is a real number. Let \(S\) consist of the spheres \(A\) and \(B\) centered at the origin with radii \(0

Find the work required to move an object in the following force fields along a line segment between the given points. Check to see whether the force is conservative. $$\mathbf{F}=\langle x, 2\rangle \text { from } A(0,0) \text { to } B(2,4)$$

Let S be the disk enclosed by the curve \(C: \mathbf{r}(t)=\langle\cos \varphi \cos t, \sin t, \sin \varphi \cos t\rangle,\)for \(0 \leq t \leq 2 \pi,\) where \(0 \leq \varphi \leq \pi / 2\) is a fixed angle. Consider the vector field \(\mathbf{F}=\mathbf{a} \times \mathbf{r},\) where \(\mathbf{a}=\left\langle a_{1}, a_{2}, a_{3}\right\rangle\) is a constant nonzero vector and \(\mathbf{r}=\langle x, y, z\rangle .\) Show that the circulation is a maximum when a points in the direction of the normal to \(S\).

Suppose an object with mass \(m\) moves in a region \(R\) in a conservative force field given by \(\mathbf{F}=-\nabla \varphi\) where \(\varphi\) is a potential function in a region \(R .\) The motion of the object is governed by Newton's Second Law of Motion, \(\mathbf{F}=m \mathbf{a}\) where a is the acceleration. Suppose the object moves from point \(A\) to point \(B\) in \(R\). a. Show that the equation of motion is \(m \frac{d \mathbf{v}}{d t}=-\nabla \varphi\) b. Show that \(\frac{d \mathbf{v}}{d t} \cdot \mathbf{v}=\frac{1}{2} \frac{d}{d t}(\mathbf{v} \cdot \mathbf{v})\) c. Take the dot product of both sides of the equation in part (a) with \(\mathbf{v}(t)=\mathbf{r}^{\prime}(t)\) and integrate along a curve between \(A\) and \(B\). Use part (b) and the fact that \(\mathbf{F}\) is conservative to show that the total energy (kinetic plus potential) \(\frac{1}{2} m|\mathbf{v}|^{2}+\varphi\) is the same at \(A\) and \(B\). Conclude that because \(A\) and \(B\) are arbitrary, energy is conserved in \(R\)

Let \(S\) be the cylinder \(x^{2}+y^{2}=a^{2},\) for \(-L \leq z \leq L\) a. Find the outward flux of the field \(\mathbf{F}=\langle x, y, 0\rangle\) across \(S\) b. Find the outward flux of the field \(\mathbf{F}=\frac{\langle x, y, 0\rangle}{\left(x^{2}+y^{2}\right)^{p / 2}}=\frac{\mathbf{r}}{|\mathbf{r}|^{p}}\) across \(S,\) where \(|\mathbf{r}|\) is the distance from the \(z\) -axis and \(p\) is a real number. c. In part (b), for what values of \(p\) is the outward flux finite as \(a \rightarrow \infty\) (with \(L\) fixed)? d. In part (b), for what values of \(p\) is the outward flux finite as \(L \rightarrow \infty\) (with \(a\) fixed)?

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