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Difference Between Dot Product and Cross Product for JEE Main 2024

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Last updated date: 28th May 2024
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What is Dot Product and Cross Product: Introduction

Explain Dot Product and Cross Product: In the realm of physics, vectors play a crucial role in describing and analyzing the physical world. Two fundamental vector operations, the dot product, and the cross product, serve as indispensable tools in various branches of physics, from mechanics to electromagnetism. Understanding the key distinctions between these two operations is essential for comprehending the underlying principles and applying them to real-world problems.


Category:

JEE Main Difference Between

Content-Type:

Text, Images, Videos and PDF

Exam:

JEE Main

Topic Name:

Difference Between Dot Product and Cross Product

Academic Session:

2024

Medium:

English Medium

Subject:

Mathematics

Available Material:

Chapter-wise Difference Between Topics


In this article, we will deal with the question “what is dot product and cross product?”, unraveling the unique characteristics of dot product and cross product and shedding light on their diverse applications. By exploring their mathematical formulations, physical interpretations, and practical implications, we aim to provide a comprehensive understanding of these fundamental vector operations from a physics perspective.


Defining Dot Product

In physics, the dot product, also known as the scalar product or inner product, is a mathematical operation that combines two vectors to yield a scalar quantity. It is denoted by the symbol "·". The dot product operates on vectors and produces a scalar value, which represents the projection of one vector onto the direction of another vector. Some characteristics of dot product are listed below:


  • Mathematical Formulation: Given two vectors, A and B, their dot product is calculated as the product of their magnitudes and the cosine of the angle θ between them:

A · B = |A| |B| cos(θ)

  • Geometrical Interpretation: The dot product allows us to determine the degree of alignment or the extent to which two vectors are pointing in the same direction. If the dot product is positive, the vectors are generally pointing in the same direction; if it is negative, they are pointing in opposite directions; and if it is zero, the vectors are orthogonal.

  • Work and Energy: In physics, the dot product finds application in the context of work and energy. When a force acts on an object and displaces it, the work done by that force is given by the dot product of the force and the displacement vectors. This relationship allows us to calculate the amount of work done and understand how energy is transferred.

  • Angle Between Vectors: By rearranging the formula, we can express the angle θ in terms of the dot product and the magnitudes of the vectors:

$\cos \theta = \dfrac{A \cdot B}{|A| |B|}$

  • Projection: The dot product enables us to find the projection of one vector onto another. The scalar projection of vector A onto vector B can be calculated as

$A_{proj} = |A| \cos \theta = \dfrac{|A|(A \cdot B)}{|A| |B|} = \dfrac{A \cdot B}{|B|}$

  • Orthogonality and Perpendicularity: Two vectors are orthogonal (perpendicular) if their dot product is zero.


The dot product provides insights into the relationships between vectors, enables calculations involving work and energy, and serves as a powerful tool in various fields of physics, including mechanics, electromagnetism, and quantum mechanics.


Defining Cross Product

In physics, the cross product, also known as the vector product, is a mathematical operation that combines two vectors to yield a third vector. Unlike the dot product, the cross product does not produce a scalar quantity but rather a vector that is perpendicular to both of the original vectors. The cross product is denoted by the symbol "×". Some characteristics of cross product are listed below:


  • Mathematical Formulation: Given two vectors, A and B, their cross product is calculated as

A × B = |A| |B| sin(θ) n

where |A| and |B| are the magnitudes of the vectors, θ is the angle between them, and n is a unit vector perpendicular to the plane defined by A and B. The direction of the cross-product is determined by the right-hand rule.

  • Geometrical Interpretation: The cross product yields another vector that is perpendicular to both of the original vectors. This vector is normal to the plane formed by the original vectors and has a magnitude equal to the product of the magnitudes of the vectors multiplied by the sine of the angle between them.

  • Torque and Angular Momentum: In physics, the cross-product finds significant applications in the context of torque and angular momentum. The torque exerted on an object is given by the cross-product of the position vector and the force vector acting on it. Similarly, the angular momentum of a rotating object is determined by the cross-product of its position vector and its linear momentum.

  • Area and Volume: The magnitude of the cross-product between two vectors is proportional to the area of the parallelogram formed by those vectors. Similarly, the magnitude of the cross-product between three vectors is proportional to the volume of the parallelepiped spanned by those vectors.


The cross-product is a fundamental operation in vector analysis, providing insights into the relationships between vectors and their perpendicularity.


Dot Product and Cross Product Difference

The dot product and cross product difference can be done by the characteristics of dot product and cross product.


S. No

Category

Dot Product

Cross Product

1

Mathematical Formulation

Given two vectors, A and B, their dot product is calculated as the product of their magnitudes and the cosine of the angle θ  between them:

A · B = |A| |B| cos(θ)

Given two vectors, A and B, their cross product is calculated as

A × B = |A| |B| sin(θ) n

where |A| and |B| are the magnitudes of the vectors, θ is the angle between them, and n is a unit vector perpendicular to the plane defined by A and B.

2

Resulting Quantity

The dot product yields a scalar quantity.

The cross-product yields a vector quantity.

3

Direction

Dot product of two vectors yields a scalar quality. So, it only has a magnitude and no direction.

Cross-product of two vectors yields a vector quantity. The direction of that vector is perpendicular to both the original vectors, which can be determined by the right-hand rule.

4

Dimensionality

It is defined for vectors in any dimension, including 2D and 3D.

The cross-product is specifically defined for vectors in 3D.

5

Examples in Physics

In physics, the dot product finds application in the context of work and energy. When a force acts on an object and displaces it, the work done by that force is given by the dot product of the force, and the displacement vectors.

In physics, the cross-product finds significant applications in the context of torque and angular momentum. The torque exerted on an object is given by the cross-product of the position vector and the force vector acting on it. 

6

Applications

The dot product is used to determine the angle between vectors, calculate work and energy in physics, and find the projection of one vector onto another.

The cross-product is a fundamental operation in vector analysis, providing insights into the relationships between vectors and their perpendicularity.


Summary

From this article, it can be concluded that the dot product yields a scalar and determines alignment, while the cross product yields a vector and determines perpendicularity. They have different mathematical formulations, resulting quantities, and applications, making them distinct operations in vector mathematics with unique properties and purposes.

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FAQs on Difference Between Dot Product and Cross Product for JEE Main 2024

1. What is the mathematical formula for the dot product of two vectors?

Given two vectors, A and B, their dot product is calculated as the product of their magnitudes and the cosine of the angle \theta between them:

A · B = |A| |B| cos(θ)

2. Explain dot product and cross product in one line.

Dot product: The dot product combines two vectors to yield a scalar representing their alignment.

Cross product: The cross product combines two vectors to yield a vector perpendicular to both original vectors.

3. How to determine the direction of the cross-product of two vectors?

The direction of that vector is perpendicular to both the original vectors, which can be determined by the right-hand rule.

4. How check the orthogonality of two vectors?

Two vectors are orthogonal (perpendicular) if their dot product is zero.

5. Give an example of the dot product from physics.

In physics, the dot product finds application in the context of work and energy. When a force acts on an object and displaces it, the work done by that force is given by the dot product of the force, and the displacement vectors.