Flux and circulation of a vector field

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Find the flux of the vector r→\overrightarrow {r}: (1) through the lateral surface of the cone x2+y2⩽z2x^{2}+y^{2}\leqslant z^{2} (0⩽z⩽h)(0\leqslant z\leqslant h); (2) through the base of this cone.

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(a)
(b)

Find the flux of the vector a→=yzi→+zxj→+xyk→\overrightarrow {a}=yz\overrightarrow {i}+zx\overrightarrow {j}+xy\overrightarrow {k}: (a) through the lateral surface of the cylinder x2+y2⩽a2x^{2}+y^{2}\leqslant a^{2} (0⩽z⩽h)(0\leqslant z\leqslant h); (б) through the entire surface of this cylinder.

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(a)
(b)

Find the flux of the radius vector r→\overrightarrow {r} through the surface

z=1−x2+y2(0⩽z⩽1) z = 1-\sqrt{x^{2}+y^{2}} \qquad (0\leqslant z\leqslant 1)
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Find the flux of the vector a→=x2i→+y2j→+z2k→\overrightarrow {a}=x^{2}\overrightarrow {i}+y^{2}\overrightarrow {j}+z^{2}\overrightarrow {k} through the part of the sphere x2+y2+z2=1x^{2}+y^{2}+z^{2}=1, x⩾0x\geqslant 0, y⩾0y\geqslant 0, z⩾0z\geqslant 0, lying in the first octant.

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Find the flux of the vector a→=yi→+zj→+xk→\overrightarrow {a}=y\overrightarrow {i}+z\overrightarrow {j}+x\overrightarrow {k} through the entire surface of the pyramid bounded by the planes x=0x=0, y=0y=0, z=0z=0, x+y+z=ax+y+z=a (a>0)(a>0).

Verify the result using the Ostrogradsky formula.

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Prove that the flux of the vector a→\overrightarrow {a} through the surface SS given by the equation r→=r→(u,v)\overrightarrow {r}=\overrightarrow {r}(u,v) ((u,v)∈Ω)((u,v)\in \Omega ) equals

∬Sa→⋅n→ dS=∬Ω(a→ ∂r→∂u ∂r→∂v) du dv, \iint _{S} \overrightarrow {a}\cdot \overrightarrow {n}\, dS = \iint _{\Omega } \left(\overrightarrow {a}\ \dfrac {\partial \overrightarrow {r}}{\partial u}\ \dfrac {\partial \overrightarrow {r}}{\partial v}\right)\, du\, dv ,

where n→\overrightarrow {n} is the unit normal vector of the surface SS.

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Find the flux of the vector a→=mr→r3\overrightarrow {a}=m\dfrac {\overrightarrow {r}}{r^{3}} (mm a constant) through a closed surface SS surrounding the origin.

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Given the vector

a→(r→)=a→∑i=1ngrad⁡(−ei4πri), \overrightarrow {a}(\overrightarrow {r}) = \overrightarrow {a}\sum _{i=1}^{n} \operatorname {grad}\left(-\dfrac {e_{i}}{4\pi r_{i}}\right) ,

where eie_{i} are constants and rir_{i} is the distance from the point MiM_{i} (the starting point) to the moving point M(r→)M(\overrightarrow {r}). Find the flux of this vector through a closed surface SS surrounding the points MiM_{i} (i=1,2,…,n)(i=1,2,\ldots ,n).

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Find the work of the vector a→=r→\overrightarrow {a}=\overrightarrow {r} along the segment of the helix

r→=acos⁡t i→+asin⁡t j→+bt k→(0⩽t⩽2π) \overrightarrow {r} = a\cos t\, \overrightarrow {i}+a\sin t\, \overrightarrow {j}+bt\, \overrightarrow {k} \qquad (0\leqslant t\leqslant 2\pi )
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Find the work of the vector a→=f(r)r→\overrightarrow {a}=f(r)\overrightarrow {r} (where ff is a continuous function) along the arc ABAB.

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Find the circulation of the vector

a→=−yi→+xj→+ck→ \overrightarrow {a} = -y\overrightarrow {i}+x\overrightarrow {j}+c\overrightarrow {k}

(cc a constant): (1) along the circle x2+y2=1x^{2}+y^{2}=1, z=0z=0; (2) along the circle (x−2)2+y2=1(x-2)^{2}+y^{2}=1, z=0z=0.

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(a)
(b)

Find the circulation Γ\Gamma of the vector a→=grad⁡(arctan⁡yx)\overrightarrow {a}=\operatorname {grad}\left(\arctan \dfrac {y}{x}\right) along a closed contour CC: (1) CC does not encircle the OzOz axis; (2) CC encircles the OzOz axis.

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(a)
(b)

References

[Dem97] Demidovich B.P. Сборник задач и упражнений по математическому анализу. 13-е изд., Издательство Московского университета / Издательство "ЧеРо", 1997.