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JoVE Core
Physics

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### 2.11: Gradient and Del Operator

In mathematics and physics, the gradient and del operator are fundamental concepts used to describe the behavior of functions and fields in space. The gradient is a mathematical operator that gives both the magnitude and direction of the maximum spatial rate of change. Consider a person standing on a mountain. The slope of the mountain at any given point is not defined unless it is quantified in a particular direction. For this reason, a "directional derivative" is defined, which is a vector that gives the slope and direction. The gradient of the scalar field satisfies both these conditions.

The gradient has the following general properties: (1) It operates on a scalar function and results in a vector function. (2) It is normal to a constant value surface. This property is used extensively to identify the direction of vector fields. (3) The gradient always points toward the maximum change in the scalar function.

Mathematically, the gradient of a scalar function is expressed as Here, 'p' is the scalar function. The term in the parenthesis is called the del operator. The del operator is a vector operator that acts on vector and scalar fields. It is a mathematical operator that, by itself, has no geometrical meaning. It is the interaction of the del operator with other quantities that gives it geometric significance. X 