Chapter 6: Problem 122
For the following exercises, determine whether the vector field is conservative and, if so, find a potential function. $$ \mathbf{F}(x, y, z)=3 z^{2} \mathbf{i}-\cos y \mathbf{j}+2 x z \mathbf{k} $$
Short Answer
Expert verified
The vector field is not conservative, so no potential function exists.
Step by step solution
01
Check for Conservativeness
A vector field is conservative if the curl of the vector field is zero. Calculate the curl of \( \mathbf{F}(x, y, z) = (3z^2, -\cos y, 2xz) \) using the formula for curl: \[ abla \times \mathbf{F} = \left( \frac{\partial F_3}{\partial y} - \frac{\partial F_2}{\partial z} \right) \mathbf{i} + \left( \frac{\partial F_1}{\partial z} - \frac{\partial F_3}{\partial x} \right) \mathbf{j} + \left( \frac{\partial F_2}{\partial x} - \frac{\partial F_1}{\partial y} \right) \mathbf{k} \]Compute each component of the curl:
02
Compute Component i of Curl
Compute \( \frac{\partial F_3}{\partial y} - \frac{\partial F_2}{\partial z} \): - \( \frac{\partial 2xz}{\partial y} = 0 \)- \( \frac{\partial (-\cos y)}{\partial z} = 0 \)So, the \( \mathbf{i} \)-component is \( 0 - 0 = 0 \).
03
Compute Component j of Curl
Compute \( \frac{\partial F_1}{\partial z} - \frac{\partial F_3}{\partial x} \):- \( \frac{\partial (3z^2)}{\partial z} = 6z \)- \( \frac{\partial (2xz)}{\partial x} = 2z \)So, the \( \mathbf{j} \)-component is \( 6z - 2z = 4z \).
04
Compute Component k of Curl
Compute \( \frac{\partial F_2}{\partial x} - \frac{\partial F_1}{\partial y} \):- \( \frac{\partial (-\cos y)}{\partial x} = 0 \)- \( \frac{\partial (3z^2)}{\partial y} = 0 \)So, the \( \mathbf{k} \)-component is \( 0 - 0 = 0 \).
05
Conclusion on Conservativeness
The curl of \( \mathbf{F} \) is \( abla \times \mathbf{F} = (0, 4z, 0) \). Since the curl is not zero everywhere, the vector field is not conservative. Therefore, there is no potential function.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Curl of a Vector Field
The curl of a vector field is a concept in vector calculus, which helps in determining whether a vector field is conservative or not. To calculate the curl, you use the formula: \[ abla \times \mathbf{F} = \left( \frac{\partial F_3}{\partial y} - \frac{\partial F_2}{\partial z} \right) \mathbf{i} + \left( \frac{\partial F_1}{\partial z} - \frac{\partial F_3}{\partial x} \right) \mathbf{j} + \left( \frac{\partial F_2}{\partial x} - \frac{\partial F_1}{\partial y} \right) \mathbf{k} \]where \( F_1, F_2, \) and \( F_3 \) are the components of the vector field \( \mathbf{F} \). This formula consists of partial derivatives that check the rotational tendencies of the vector field.
- The curl helps indicate if the field exhibits any rotational movement or swirl.
- If the curl is zero, the vector field is conservative in which the field has no rotational aspect.
- A conservative vector field can have a potential function, meaning it can be expressed as the gradient of some scalar function.
Potential Function
A potential function is a scalar function whose gradient is equal to a given vector field. For a vector field to have a potential function, it must be conservative, meaning its curl must be zero everywhere.
In the problem discussed, \( \mathbf{F}(x, y, z) \) was determined to not be conservative as its curl was not zero due to the \( 4z \) component. Therefore, it cannot have a potential function since not all parts of the curl are zero.
- The existence of a potential function implies that the vector field is path-independent: the line integral between two points is the same regardless of the path taken.
- This property is valuable in physics, for example, in cases like gravitational and electrostatic fields.
In the problem discussed, \( \mathbf{F}(x, y, z) \) was determined to not be conservative as its curl was not zero due to the \( 4z \) component. Therefore, it cannot have a potential function since not all parts of the curl are zero.
Vector Calculus
Vector calculus is a branch of mathematics that deals with vector fields and differentiable functions of multiple variables. It provides tools for understanding physical phenomena like fluid flow, electromagnetism, and classical mechanics.
- Some notable operations in vector calculus include divergence, curl, and gradient.
- The gradient of a scalar function develops a vector field, indicating the direction of greatest increase.
- The divergence measures the magnitude of a source or sink at a given point.
- Curl, as mentioned earlier, reveals the rotational nature of a vector field.