Question

Consider a cube of unit edge length and sides parallel to co-ordinate axes, with its centroid at the point (1, 2, 3). The surface integral  A F . d A of a vector field  F = 3 x i ^ + 5 y j ^ + 6 z k ^ over the entire surface A of the cube is ______.

Options :

  1. 14

  2. 27

  3. 28

  4. 31

Show Answer

Answer :

14

Solution :

V = volume of cube = (1)3

F = 3 x i ^ + 5 y j ^ + 6 z k ^

. F = δ δ x ( 3 x ) + δ δ y ( 5 y ) + δ δ z ( 6 z )  = 3 + 5 + 6 = 14

A F . d A = V . F d V

A F . d A = V 14   d V  = 14 × ( V )

A F . d A  = 14

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