Chapter 26: Problem 6
A vector field is given by $$ \begin{aligned} \mathbf{F}=&\left(3 x^{2}-z\right) \mathbf{i}+(2 x+y) \mathbf{j} \\ &+(x+3 y z) \mathbf{k} \end{aligned} $$ Find \(\nabla \cdot \mathbf{F}\) at the point \((1,2,3)\).
Short Answer
Expert verified
The divergence \( \nabla \cdot \mathbf{F} \) at the point \((1,2,3)\) is 13.
Step by step solution
01
Understand the Divergence Formula
The divergence of a vector field \( \mathbf{F} = P\mathbf{i} + Q\mathbf{j} + R\mathbf{k} \) is given by \( abla \cdot \mathbf{F} = \frac{\partial P}{\partial x} + \frac{\partial Q}{\partial y} + \frac{\partial R}{\partial z} \). Identify each component of \( \mathbf{F} \): \( P = 3x^2 - z \), \( Q = 2x + y \), and \( R = x + 3yz \).
02
Compute the Partial Derivative with Respect to x
Compute the partial derivative of \( P \) with respect to \( x \): \( \frac{\partial P}{\partial x} = \frac{\partial}{\partial x}(3x^2 - z) = 6x \).
03
Compute the Partial Derivative with Respect to y
Compute the partial derivative of \( Q \) with respect to \( y \): \( \frac{\partial Q}{\partial y} = \frac{\partial}{\partial y}(2x + y) = 1 \).
04
Compute the Partial Derivative with Respect to z
Compute the partial derivative of \( R \) with respect to \( z \): \( \frac{\partial R}{\partial z} = \frac{\partial}{\partial z}(x + 3yz) = 3y \).
05
Calculate the Divergence
Use the results from the partial derivatives to calculate the divergence: \( abla \cdot \mathbf{F} = 6x + 1 + 3y \).
06
Evaluate at the Point (1,2,3)
Substitute \( x = 1 \), \( y = 2 \), and \( z = 3 \) into the divergence equation: \( abla \cdot \mathbf{F} = 6(1) + 1 + 3(2) = 6 + 1 + 6 = 13 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Divergence
Divergence is a fundamental concept in vector calculus that measures how much a vector field spreads out from a point. Contrary to curl, which measures rotation, divergence tells us about the expansion or contraction at a point within a field. To compute divergence, we use the formula:
- For a vector field \( \mathbf{F} = P\mathbf{i} + Q\mathbf{j} + R\mathbf{k} \), divergence is \( abla \cdot \mathbf{F} = \frac{\partial P}{\partial x} + \frac{\partial Q}{\partial y} + \frac{\partial R}{\partial z} \).
Partial Derivatives
Partial derivatives are central to understanding the behavior of multivariable functions, like those seen in vector calculus. In essence, a partial derivative measures the rate of change of a function with respect to one variable, while other variables are held constant.For example:
- The partial derivative \( \frac{\partial P}{\partial x} \) tells us how much the function \( P \) changes as \( x \) changes, keeping other variables like \( y \) and \( z \) fixed.
Vector Field
A vector field is a mathematical construction where a vector is assigned to every point in a given space or plane. This approach provides a way to model various physical phenomena, such as fluid flow, magnetic fields, and gravitational fields.The given vector field for this exercise is \( \mathbf{F} = (3x^2 - z) \mathbf{i} + (2x + y) \mathbf{j} + (x + 3yz) \mathbf{k} \), consisting of components \( P \), \( Q \), and \( R \) assigned to the \( x \), \( y \), and \( z \) directions respectively.
- Understanding each component's role is key to interpreting the overall behavior of the field.
Mathematical Solution Process
The mathematical solution process involves systematically applying theory to solve problems step-by-step. This not only provides a structured approach to math challenges but also ensures accuracy and understanding.
For example, in finding the divergence at a specific point, follow these steps:
- Identifying each component of the vector field.
- Computing partial derivatives for these components.
- Using partial derivatives to compute the divergence.
- Evaluating the calculated divergence at the given point.