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For a position vector r = x î + y ĵ + z k̂ the norm of the vector can be defined as |r| = √(x² + y² + z²). Given a function ϕ = ln|r|, its gradient ∇ϕ is
- r
- r/|r|
- r/(r·r)
- r/|r|³
Correct answer: r/(r·r)
Solution
The gradient of the function ϕ = ln|r| involves the derivative of the logarithm of the norm of the vector, which leads to a result that is proportional to the vector itself divided by the square of its magnitude. This is consistent with the formula for the gradient of a logarithmic function, resulting in the correct option being r/(r·r).
Related GATE Engineering Mathematics questions
- A vector field p and a scalar field r are given by
p = (2x² - 3xy + z²) î + (2y² - 3yz + x²) ĵ + (2z² - 3xz + x²) k̂
r = 6x² + 4y² - z² - 9xyz - 2xy + 3xz - yz
Consider the statements P and Q.
P: Curl of the gradient of the scalar field r is a null vector.
Q: Divergence of curl of the vector field p is zero.
Which one of the following options is CORRECT?
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- A delivery agent is at a location R. To deliver the order, she is instructed to travel to location P along straight-line paths of RC, CA, AB and BP of 5 km each. The direction of each path is given in the table below as whole circle bearings. Assume that the latitude (L) and departure (D) of R is (0, 0) km. What is the latitude and departure of P (in km, rounded off to one decimal place)? Paths: RC, CA, AB, BP. Directions (in degrees): 120, 0, 90, 240.
- Three vectors p, q and r are given as p = î + ĵ + k̂, q = î + 2ĵ + 3k̂, r = 2î + 3ĵ + 4k̂. Which of the following is/are CORRECT?
- If a vector field V is related to another vector field A through V = ∇ × A, which of the following is true? Note: C and S_c refer to any closed contour and any surface whose boundary is C.
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