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GATE 2017 EC (EC2) – Question 38

Engineering Mathematics · Vector Analysis · 2 marks · Multiple choice

If $\mathbf F=\hat a_x(3y-k_1z)+\hat a_y(k_2x-2z)-\hat a_z(k_3y+z)$ is irrotational, the constants $k_1,k_2,k_3$, respectively, are

  1. 0.3, −2.5, 0.5
  2. 0.0, 3.0, 2.0
  3. 0.3, 0.33, 0.5
  4. 4.0, 3.0, 2.0

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Correct answer: (B) 0.0, 3.0, 2.0

Explanation

An irrotational vector field has zero curl. For the given components, the curl is
$$\nabla\times\mathbf F=(2-k_3)\hat a_x-k_1\hat a_y+(k_2-3)\hat a_z.$$
Each coefficient must vanish independently. Hence $k_3=2$, $k_1=0$ and $k_2=3$.

In the requested order the triple is **(0,3,2), B**.

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