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Volume Integrals

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VOLUME INTEGRALS:

Let f be a scalar function and V is a volume enclosed by a surface S in xyz plane then the
integral of scalar function f over volume V is volume integral and is given by
x2 y 2 z 2

V=  V
f dxdydz     f dzdydx
x1 y1 z1

(OR)
Let F be a vector function and V is a volume enclosed by a surface S in xyz plane then the
integral of vector function F over volume V is volume integral and is given by
x2 y 2 z 2

V= V
F dxdydz     F dzdydx
x1 y1 z1

PROBLEMS:

1. If F  (2 x 2  3z)i  2xyj  4 xk Evaluate    Fdv


V
where V is the closed region

bounded by the planes x = 0, y = 0, z = 0 and the plane 2x+2y+z = 4


   
Sol:   F   i  j  k   (2 x 2  3z )i  2 xyj  4 xk = 4x-2x+0 = 2x.
 x y z 

Limits of z: 0 to 4-2x-2y

Limits of y: 0 to 2-x

Limits of x: 0 to 2
2 2 x 4 2 x 2 y 2 2 x 4 2 x  2 y 2 2 x

   Fdv  
V
0

0
 2 x dzdydx  
0 0
 2 x z 
0
dydx  
0
 2 x 4  2 x  2 ydydx
0
0

2 2 x 2 2 x 2 x
 2
y2 
 4
0
 x 2  x  ydydx  4
0 0
0 x ( 2  x )  xy dydx  4 0  x ( 2  x ) y  x  dx
2 0
2
 (2  x) 2 
2 2
 4   x( 2  x) 2  x dx  2  x ( 2  x ) 2
dx  2  x(4  x 2  4 x)dx
0 
2  0 0

2
2
 x4 x3   32   32  8
 2 (4 x  x  4 x )dx  22 x 2 
3 2
 4   28  4    212   
0  4 3 0  3  3 3

22
Dr. K.S. Balamurugan, RVR & JC College of Engineering, Guntur, A.P

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