Question Details

32.  Given that  F ( x , y , z ) = sin ( y ) i ^ + cos ( x ) j ^ + 5 k ^ ,  the integral  S F · d S  over the unit sphere  S  centered at the origin evaluates to _______.  (Round off to one

decimal place)

Options

A

0

B

1

C

5

D

7

Show Answer

Correct Answer :

Option A

0

Solution :

The correct answer is Option A: 0 (or simply 0).

To evaluate the surface integral of the vector field F(x,y,z)=sin(y)i^+cos(x)j^+5k^ over the closed unit sphere S centered at the origin, we can apply the Divergence Theorem.

The Divergence Theorem states that for a vector field F and a solid region V enclosed by a closed surface S with an outward orientation:
SF·dS=V(·F)dV

First, let us calculate the divergence of the vector field F, denoted as ·F. The components of F=Pi^+Qj^+Rk^ are:
P(x,y,z)=sin(y)
Q(x,y,z)=cos(x)
R(x,y,z)=5

Now, compute the partial derivatives for the divergence:
Px=x(sin(y))=0
Qy=y(cos(x))=0
Rz=z(5)=0

Summing these partial derivatives gives the divergence of the vector field:
·F=Px+Qy+Rz=0+0+0=0

Since the divergence of F is zero everywhere in the solid sphere V, the triple integral of the divergence over V evaluates to:
V(·F)dV=V0dV=0

Therefore, by the Divergence Theorem, the flux of F across the unit sphere is:
SF·dS=0

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