Proving B.(Gradient . B) - B X (Gradient X B)=Del{i}B{i}B{j}

  • Thread starter hellomynameisscottt
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In summary, the formula B.(Gradient . B) - B X (Gradient X B)=Del{i}B{i}B{j} is derived from the triple product rule and shows the relationship between the gradient and curl of a vector field. Each term in the equation represents a different operation on the vector field. This formula is significant in physics and has practical applications in various fields such as electromagnetism, fluid mechanics, and data analysis.
  • #1
hellomynameisscottt
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Homework Statement


I need to prove B.(Gradient . B) - B X(Gradient X B)=Del{i} [B{i}B{j} -1/2 (kroneker delta {ij} B^2]

where I have used . as the dot product, {} as subscript. Thank you!

Homework Equations

The Attempt at a Solution


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I have attempted the solution but am not sure how it is possible to keep a kroneker delta on the right hand side.
 
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  • #2
I can not read your complete statement above, but this looks like it comes from a standard vector identity: (where ## A ## and ## B ## are both equal to ## B ##).
## \nabla (A \cdot B)=(A \cdot \nabla) B +(B \cdot \nabla) A+A \times \nabla \times B+B \times \nabla \times A ##
 
  • #3
I have uploaded the page from Jackson it is equation (6.119) I am trying to prove, however I must use Levi Cevita notation.
 

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  • #4
hellomynameisscottt said:
I have uploaded the page from Jackson it is equation (6.119) I am trying to prove, however I must use Levi Cevita notation.
On the left side of the equation in your OP, they are only taking one component. You may be able to use the identity I presented to simplify the ## B \times \nabla \times B ## term.
 

Related to Proving B.(Gradient . B) - B X (Gradient X B)=Del{i}B{i}B{j}

1. What is the formula for proving B.(Gradient . B) - B X (Gradient X B)=Del{i}B{i}B{j}?

The formula for proving B.(Gradient . B) - B X (Gradient X B)=Del{i}B{i}B{j} is a mathematical equation used in vector calculus to show the relationship between the gradient of a vector field and its curl. It is often used in electromagnetism and fluid mechanics.

2. How is this formula derived?

This formula is derived using the vector identity known as the triple product rule, which states that the dot and cross product of three vectors can be interchanged with the del operator. By applying this rule to the original equation, we can rearrange and simplify it to get the desired result.

3. What does each term in the equation represent?

The term B.(Gradient . B) represents the dot product of the vector field B with the gradient of B. The term B X (Gradient X B) represents the cross product of B with the curl of B. The term Del{i}B{i}B{j} represents the del operator applied to the product of two components of B.

4. What is the significance of this formula in physics?

This formula is significant in physics because it relates the gradient and curl of a vector field, which are important concepts in electromagnetism and fluid mechanics. It can be used to solve problems involving the behavior of electric and magnetic fields, as well as the flow of fluids.

5. Are there any practical applications of this formula?

Yes, there are many practical applications of this formula in various fields of science and engineering. For example, it can be used to study the flow of air around an airplane wing or the behavior of magnetic fields in a fusion reactor. It is also used in computer simulations to model complex systems and in data analysis to extract meaningful information from experimental data.

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