Evaluate ∫SF⃗ ⋅dA⃗ , where F⃗ =(bx/a)i⃗ +(ay/b)j⃗ and S is the elliptic cylinder oriented away from the z-axis, and given by x2/a2+y2/b2=1, |z|≤c, where a, b, c are positive constants.

Respuesta :

Answer:

Therefore surface integral is [tex]\pi(a^2+b^2)c-0-0=\pi(a^2+b^2)c[/tex].

Step-by-step explanation:

Given function is,

[tex]\vec{F}=\frac{bx}{a}\uvec{i}+\frac{ay}{b}\uvec{j}[/tex]

To find,

[tex]\int\int_{S}\vec{F}dS[/tex]  

where S=A=surfece of elliptic cylinder we have to apply Divergence theorem so that,

[tex]\int\int_{S}\vec{F}dS[/tex]

[tex]=\int\int\int_V\nabla.\vec{F}dV[/tex]

[tex]=\int\int\int_V(\frac{b}{a}+\frac{a}{b})dV[/tex]  

[tex]=\frac{a^2+b^2}{ab}\int\int\int_VdV[/tex]

[tex]=\frac{a^2+b^2}{ab}\times \textit{Volume of the elliptic cylinder}[/tex]

[tex]=\frac{a^2+b^2}{ab}\times \pi ab\times 2c=\pi (a^2+b^2)c[/tex]

  • If unit vector [tex]\cap{n}[/tex] directed in positive (outward) direction then z=c and,

[tex]\int\int_{S_1}\vex{F}.dS_1=\int\int_{S_1}<\frac{bx}{a}, \frac{ay}{b}, 0> . <-z_x,z_y,1>dA[/tex]      

[tex]=\int\int_{S_1}<\frac{bx}{a},\frac{ay}{b}, 0>.<0,0,1>dA=0[/tex]

  • If unit vector [tex]\cap{n}[/tex] directed in negative (inward) direction then z=-c and,

[tex]\int\int_{S_2}\vex{F}.dS_2=\int\int_{S_2}<\frac{bx}{a}, \frac{ay}{b}, 0>. -<-z_x,z_y,1>dA[/tex]      

[tex]=\int\int_{S_2}<\frac{bx}{a},\frac{ay}{b}, 0>. -<0,0,1>dA=0[/tex]

Therefore surface integral without unit vector of the surface is,

[tex]\pi(a^2+b^2)c-0-0=\pi(a^2+b^2)c[/tex]

The value of ∫SF ⋅dA where F =(bx/a)i +(ay/b)j and S is the elliptic cylinder oriented away from the z-axis is 2πc(a² + b²).

How to solve the elliptic cylinder?

From the information, F = (b/ax) + (a/by)j and S is the elliptic cylinder.

To evaluate ∫F.dA goes thus:

divF = (I'd/dx + jd/dx + kd/dx) × (b/ax)i + (a/by)j

= b/a + a/b

= (a² + b²)/ab

Using Gauss divergence theorem, this will be further solved below:

∫∫∫v(a² + b²/ab)dV

= (a² + b²/ab)∫∫∫vdV

= (a² + b²/ab) × Volume of cylinder

= (a² + b²/ab) × πab(2c)

= 2πc(a² + b²)

Learn more about cylinder on:

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