Conditions for a Scalar Field Identity

Here explains a vector identity proof by simplifying both sides of an equation using the vector triple product and gradient product rules, ultimately showing that the identity holds only if the scalar field $\phi$ satisfies Laplace's equation ( $\nabla^2 \phi=0$ ). This means the scalar field must be a harmonic function. This theoretical concept is then made practical and intuitive by an app that visually connects a scalar field to its gradient vector field, allowing users to interactively explore these principles and identify harmonic functions.

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✍️Mathematical Proof

$\gg$Mathematical Structures Underlying Physical Laws

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Vector Identity Proof : The problem demonstrates how to prove a vector identity by expanding both sides of the equation, the Left-Hand Side (LHS) and the Right-Hand Side (RHS), and then simplifying them to find the conditions under which they are equal.
Vector Triple Product :The LHS, $\nabla \times(\nabla \phi \times a)$, is a vector triple product that simplifies to $-a\left(\nabla^2 \phi\right)$ by applying the identity $A \times(B \times C)=B(A \cdot C)-C(A \cdot B)$ and using the property that the divergence of a constant vector is zero ( $\nabla \cdot a=0$ ).
Gradient Product Rule : The RHS, $\nabla(\nabla \phi \cdot a)$, is the gradient of a dot product. It simplifies to 0 because the vector $a$ is constant, making both the terms from the product rule equal to zero.
Laplace's Equation and Harmonic Functions : For the identity to hold true, the simplified LHS must equal the simplified RHS. This leads to the condition $-a\left(\nabla^2 \phi\right)=0$. Since $a$ is a non-zero vector, the scalar quantity $\nabla^2 \phi$ must be zero. This final condition, $\nabla^2 \phi=0$, is known as Laplace's equation, and any scalar field $\phi$ that satisfies it is called a harmonic function.

🎬Demonstration

The app provides an intuitive, interactive way to understand the abstract concept of a gradient by visually connecting a scalar function to its corresponding vector field. It reinforces that the gradient is a vector that points in the direction of the steepest increase, with its magnitude representing the rate of change. Additionally, it introduces and visualizes the concept of the Laplacian, helping to identify harmonic functions.

Visualize the scalar field and its Laplacian analysis and harmonic function check