### Gradient of a Scalar T (grad T) - Definition, Significance & Solved Examples.

- The gradient of a scalar field provides a vector field that states how the scalar value is changing throughout space – a change that has both a magnitude and direction.

- A gradient is applied to a scalar quantity that is a function of a 3D vector field: position. The gradient measures the direction in which the scalar quantity changes the most, as well as the rate of change with respect to position.

- The physical meaning of the gradient of a scalar is that it represents the steepness of the slope or line. For example, height is a scalar quantity; gradient of the height would be a vector pointing upwards. The length of the vector is proportional to the steepness of the slope.

- A derivative is required that tells us how fast the function varies, if we move a little distance.

- Consider a scalar function T which is a function of space coordinates x, y and z.

- The projection or the component of ∇ T in the direction of a unit vector al is ∇ T . al and is called the DIRECTIONAL DERIVATIVE of T along unit vector. Hence dT/dl is the directional derivative of T.

- Hence we also say that, the gradient of a scalar field indicates the direction of greatest change (that is largest derivative) as well as the magnitude of that change, at every point in space.

PROPERTIES OF GRADIENT OF A SCALAR FIELD T:

- If A =∇ T, T is said to be the scalar potential of A.

- The magnitude of ∇ T equals the maximum rate of change in T per unit distance.

- ∇T points in the direction of the maximum rate of change in V.

- ∇T at any point is perpendicular to the constant T surface that passes through that point.

Gradient of a scalar T for Cartesian coordinate system is given as:

Gradient of a scalar T for Cylindrical coordinate system is given as:

Gradient of a scalar T in Spherical coordinate system is given as:

SOLVED EXAMPLES / NUMERICALS:

Q.4 Find the gradient of these scalar fields:
a) U = 4xz2 + 3yz
b) H = r2cosθ cosφ                SOLUTION/ANSWER

Q.5 If V(x, y, z) = 3x2y –y2z2, find ∇ V and |∇ V| at the point (1, 2, -1).   SOLUTION/ANSWER

Q.6 Given φ = xy +yz +xz, find gradient φ at point (1, 2, 3) and the directional derivative of φ.     SOLUTION/ANSWER

Q.7 Find V(x, y, z) if grad V = (y2 – 2xyz3)ax + (3 + 2xy – x2z3)ay + (4z3 – 3x2yz2)az and V(0, 0, 0) = -2.      SOLUTION/ANSWER

Q.8 Find the unit normal vector of the surface x2 + y2 + z2 = 14 at (-1, 3, 2) ?     SOLUTION/ANSWER

Q.9 The temperature in an auditorium is given by T = x2 + y2 – z. A mosquito located at (1, 1, 2) in the auditorium desires to fly in such a direction that it will get warm as soon as possible. In what direction must it fly?      SOLUTION/ANSWER

ALSO READ:

- Line , Surface and Volume Intergral.

- Del Operator - Definition and Significance.

- Gradient Of a Scalar (∇ V).

- Numericals / Solved Examples - Gradient Of a Scalar.

- Divergence Of a Vector ( ∇ . A ).

- Numericals / Solved Examples - Divergence Of a Vector.

- Curl Of a Vector ( ∇ x A).

- Laplacian Of a Scalar ( ∇2 V).

Short Notes/FAQ's

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