GATE AG 2021 • Q11 MCQ • 1 Mark

Section 1: Engineering Mathematics

Vector Calculus

Subtopic: Divergence and curl

Question Statement:

Let the vector $\vec{v} = v_1\hat{i} + v_2\hat{j} + v_3\hat{k}$ be a differentiable vector function of Cartesian coordinates $(x, y, z)$. The curl of vector $\vec{v}$ is:

Options:

  • (A) (∂v₂/∂z − ∂v₃/∂y)î + (∂v₃/∂x − ∂v₁/∂z)ĵ + (∂v₁/∂y − ∂v₂/∂x)k̂
  • (B) (∂v₃/∂z − ∂v₂/∂y)î + (∂v₁/∂x − ∂v₃/∂z)ĵ + (∂v₂/∂y − ∂v₁/∂x)k̂
  • (C) (∂v₃/∂y − ∂v₂/∂z)î + (∂v₁/∂z − ∂v₃/∂x)ĵ + (∂v₂/∂x − ∂v₁/∂y)k̂
  • (D) (∂v₂/∂y − ∂v₃/∂z)î + (∂v₃/∂z − ∂v₁/∂x)ĵ + (∂v₁/∂x − ∂v₂/∂y)k̂

Official Answer Key:

C

Step-by-Step Solution & Explanation

By definition, curl v⃗ = ∇ × v⃗ = det[[î,ĵ,k̂],[∂/∂x,∂/∂y,∂/∂z],[v₁,v₂,v₃]] = (∂v₃/∂y − ∂v₂/∂z)î + (∂v₁/∂z − ∂v₃/∂x)ĵ + (∂v₂/∂x − ∂v₁/∂y)k̂. This is exactly option (C), the standard determinant expansion of the curl operator.

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