Chapter 17: Problem 15
Sketch the following vector fields. $$\mathbf{F}=\langle y,-x\rangle$$
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Chapter 17: Problem 15
Sketch the following vector fields. $$\mathbf{F}=\langle y,-x\rangle$$
These are the key concepts you need to understand to accurately answer the question.
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The potential function for the force field due to a charge \(q\) at the origin is \(\varphi=\frac{1}{4 \pi \varepsilon_{0}} \frac{q}{|\mathbf{r}|},\) where \(\mathbf{r}=\langle x, y, z\rangle\) is the position vector of a point in the field, and \(\varepsilon_{0}\) is the permittivity of free space. a. Compute the force field \(\mathbf{F}=-\nabla \varphi\) b. Show that the field is irrotational; that is, show that \(\nabla \times \mathbf{F}=\mathbf{0}\)
Streamlines and equipotential lines Assume that on \(\mathbb{R}^{2}\), the vector field \(\mathbf{F}=\langle f, g\rangle\) has a potential function \(\varphi\) such that \(f=\varphi_{x}\) and \(g=\varphi_{y},\) and it has a stream function \(\psi\) such that \(f=\psi_{y}\) and \(g=-\psi_{x}\). Show that the equipotential curves (level curves of \(\varphi\) ) and the streamlines (level curves of \(\psi\) ) are everywhere orthogonal.
Heat flux The heat flow vector field for conducting objects is \(\mathbf{F}=-k \nabla T,\) where \(T(x, y, z)\) is the temperature in the object and \(k > 0\) is a constant that depends on the material. Compute the outward flux of \(\mathbf{F}\) across the following surfaces S for the given temperature distributions. Assume \(k=1\) $$T(x, y, z)=100 e^{-x^{2}-y^{2}-z^{2}} ; S \text { is the sphere } x^{2}+y^{2}+z^{2}=a^{2}$$
Consider the radial field \(\mathbf{F}=\mathbf{r} /|\mathbf{r}|^{p}\) where \(\mathbf{r}=\langle x, y, z\rangle\) and \(p\) is a real number. Let \(S\) be the sphere of radius \(a\) centered at the origin. Show that the outward flux of \(\mathbf{F}\) across the sphere is \(4 \pi / a^{p-3} .\) It is instructive to do the calculation using both an explicit and a parametric description of the sphere.
Prove that for a real number \(p,\) with \(\mathbf{r}=\langle x, y, z\rangle, \nabla \cdot \frac{\langle x, y, z\rangle}{|\mathbf{r}|^{p}}=\frac{3-p}{|\mathbf{r}|^{p}}\)
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