Calculating del(1/r) with Separation Vectors: How to Prove the Equation?

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In summary, the problem involves finding the gradient of the inverse of the magnitude of a separation vector. The correct equation for this is del(1/r) = -R/r^2, where R is the separation vector and r is the magnitude of R. The mistake in the attempt at a solution was missing the hat on R in the equation.
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Homework Statement


let R be the separation vector from (a,b,c) to (x,y,z) and r be the magnitude of R.
Show that: del(1/r) = -R/r^2

Homework Equations


del is the gradient operator

The Attempt at a Solution


The problem is that I keep getting a 3/2 power in the denominator when I calculate the left hand side.

r = sqrt((x-a)^2 + (y-b)^2 + (z-c)^2)

1/r = ((x-a)^2 + (y-b)^2 + (z-c)^2)^-0.5

del(1/r) = -R/[(x-a)^2 + (y-b)^2 + (z-c)^2]^(3/2)
 
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I see, you're right. I missed the hat on R in my text. Thanks.
 

Related to Calculating del(1/r) with Separation Vectors: How to Prove the Equation?

1. What is the proof of del(1/r) = -R/r^2?

The proof of this equation is based on the application of the vector calculus operator known as del, which represents the gradient of a function. In this case, the function is 1/r, which represents the inverse of the distance from a point in space. By applying the del operator to this function, we get the resulting expression of -R/r^2, where R is the position vector.

2. How is this equation derived?

This equation can be derived using the vector calculus identity for the gradient of an inverse function, which states that the gradient of 1/f(x) is equal to -f'(x)/[f(x)]^2. In this case, f(x) is the distance function, and f'(x) represents its derivative, which is equal to the position vector R. By substituting these values into the identity, we get the equation del(1/r) = -R/r^2.

3. What does this equation represent?

This equation represents the gradient of the inverse distance function in vector calculus. It is used to calculate the strength and direction of a field at any point in space, where the field is inversely proportional to the distance from a source. This equation is commonly used in the study of electrostatics and gravitational fields.

4. What are the practical applications of this equation?

This equation has many practical applications in various fields of science and engineering. For example, it can be used to calculate the electric field strength at any point in space due to a charged object, or the gravitational field strength due to a massive object. It is also useful in calculating the force between two objects, such as planets or charged particles.

5. Are there any limitations to this equation?

Like any mathematical equation, there are limitations to its applicability. This equation assumes a point source of the field, and therefore, it may not accurately represent more complex distributions of the field. It also assumes a continuous and smooth field, which may not always be the case in real-world scenarios. Additionally, it is based on the classical laws of physics and may not hold true in extreme conditions, such as near black holes or at quantum scales.

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