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If \(\overline{A} = x\hat{e}_{x} + y\hat{e}_{y} + z\hat{e}_{j}\), then \(\nabla^{2}\overline{A}\) will be :

  • A.1
  • B.3
  • C.0
  • D.-3

Answer: C

The Laplacian of the field is 0.

The field is the position vector, \(\overline{A} = x\hat{e}_{x} + y\hat{e}_{y} + z\hat{e}_{z}\) (the paper prints the last unit vector as \(\hat{e}_{j}\)). In Cartesian coordinates the vector Laplacian acts on each component separately, and each component is linear in the coordinates:

\[ \nabla^{2}x = \nabla^{2}y = \nabla^{2}z = 0 \]

so \(\nabla^{2}\overline{A} = 0\). The value 3 is the divergence \(\nabla \cdot \overline{A}\), a common confusion; 1 and -3 do not arise from either operation.

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