Question Details

The vector function expressed by  F = a x ( 5 y k 1 z ) + a y ( 3 z + k 2 x ) + a z ( k 3 y 4 x ) Represents a conservative field, where ax, ay, az are unit vectors along x, y and z directions, respectively. The values of constant k1, k2, k3 are given by:

Options

A

k1 = 3, k2 = 3, k3 = 7

B

k1 = 3, k2 = 8, k3 = 5

C

k1 = 4, k2 = 5, k3 = 3

D

k1 = 0, k2 = 0, k3 = 0

Correct Answer :

k1 = 4, k2 = 5, k3 = 3

Solution :

The correct option is: k1 = 4, k2 = 5, k3 = 3.

To find the values of the constants k1, k2, and k3, we use the definition of a conservative vector field.
A vector field F is conservative if and only if its curl is equal to the zero vector:
× F = 0

Let the vector field be written in terms of its components as:
F = Fx ax + Fy ay + Fz az
From the given expression of the vector field:
Fx = 5 y k1 z
Fy = 3 z + k2 x
Fz = k3 y 4 x

The curl of F in Cartesian coordinates is given by the determinant:
× F = | ax ay az x y z Fx Fy Fz |

Expanding the determinant, we get:
× F = ax ( Fzy Fyz ) ay ( Fzx Fxz ) + az ( Fyx Fxy )

For the field to be conservative, each component of the curl must be equal to zero. This yields three independent equations:
1) For the ax component:
Fzy Fyz = 0 Fzy = Fyz
2) For the ay component:
Fzx Fxz = 0 Fzx = Fxz
3) For the az component:
Fyx Fxy = 0 Fyx = Fxy

Now, we compute the partial derivatives required for each equation:
- From Equation (1):
y ( k3 y 4 x ) = k3
z ( 3 z + k2 x ) = 3
Equating them gives:
k3 = 3

- From Equation (2):
x ( k3 y 4 x ) = 4
z ( 5 y k1 z ) = k1
Equating them gives:
4 = k1 k1 = 4

- From Equation (3):
x ( 3 z + k2 x ) = k2
y ( 5 y k1 z ) = 5
Equating them gives:
k2 = 5

Combining these results, we get:
k1 = 4, k2 = 5, k3 = 3

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