## Multiplication of Vectors – Class 11 | Chapter – 4 | Physics Short Notes Series PDF for NEET & JEE

* Multiplication of Vectors:* Multiplication of vectors with a real number is known as scalar multiplication. This multiplication alters the magnitude of the vector but does not disturb its direction. However, if the multiplied quantity is negative, this would not be the case, and the direction would be reversed.

*Multiplication of Vectors by Real Numbers*

In linear algebra, multiplication of a vectors by a real number is a scalar multiplication.

Let’s assume that we have a vector **v** = [v1, v2, …, vn], and a scalar k. Then, the scalar multiplication of **v** and k is given by:

k **v** = [k*v1, k*v2, …, k*vn]

Geometrically, scalar multiplication of a vector by a positive scalar k stretches or shrinks the vector by a factor of k without changing its direction. If k is negative, the vector is also flipped in the opposite direction.

Some properties of scalar multiplication include:

- Distributive property: k(
**u**+**v**) = k**u**+ k**v** - Associative property: (k1k2)
**v**= k1(k2**v**) - Identity property: 1
**v**=**v** - Zero property: 0
**v**=**0**, where**0**is the zero vector with all components equal to zero.

Scalar multiplication is an important operation in linear algebra and is used in various applications, including matrix multiplication, linear transformations, and eigenvectors.

*Types of Multiplication of Vectors*

In linear algebra, there are different types of multiplication of vector, including the dot product, cross product, and tensor product.

**Dot Product:**

The dot product of two vectors **u** and **v** of the same dimension is defined as:

**u** ⋅ **v** = u1v1 + u2v2 + … + unvn

The dot product is a scalar value that measures the degree of similarity or orthogonality between two vectors. It is also used to calculate the length or magnitude of a vector.

Some properties of the dot product include:

- Commutative property:
**u**⋅**v**=**v**⋅**u** - Distributive property:
**u**⋅ (**v**+**w**) =**u**⋅**v**+**u**⋅**w** - Associative property: (k
**u**) ⋅**v**=**u**⋅ (k**v**) = k(**u**⋅**v**)

**Cross Product:**

The cross product of two vectors **u** and **v** in three-dimensional space is defined as:

**u** × **v** = [u2v3 – u3v2, u3v1 – u1v3, u1v2 – u2v1]

The cross product is a vector perpendicular to the plane formed by **u** and **v**. Its magnitude is proportional to the area of the parallelogram formed by **u** and **v**.

Some properties of the cross product include:

- Anti-commutative property:
**u**×**v**= –**v**×**u** - Distributive property:
**u**× (**v**+**w**) =**u**×**v**+**u**×**w** - Associative property: (k
**u**) ×**v**=**u**× (k**v**) = k(**u**×**v**)

**Tensor Product:**

The tensor product of two vectors **u** and **v** of dimension m and n, respectively, is a matrix of size mxn defined as:

**u** ⊗ **v** = | u1v1 u1v2 … u1vn | | u2v1 u2v2 … u2vn | | … … … … | | umv1 umv2 … umvn |

The tensor product is used in tensor algebra and is also used in the construction of higher-order tensors and multilinear mappings.

*Applications of Multiplication of Vectors*

Multiplication of vectors has numerous applications in various fields, including physics, engineering, computer graphics, and machine learning. Here are some examples:

In physics, multiplication of vectors is used to calculate various physical quantities, such as work, power, and torque. For instance, the dot product of the force vector and the displacement vector is used to calculate the work done by a force, while the cross product of the force vector and the displacement vector is used to calculate the torque applied by a force.**Physics:**In engineering, vector multiplication is used in structural analysis and design, motion analysis, and control systems. For example, the dot product of two vectors is used to determine the angle between them, while the cross product is used to calculate the moment of a force about a point.**Engineering:**In computer graphics, vector multiplication is used to create 3D graphics and animations. The cross product of two vectors is used to determine the direction of the normal to a plane, while the dot product is used to calculate the intensity of light on a surface.**Computer Graphics:**In machine learning, vector multiplication is used in various operations, such as vector normalization, dot products between vectors, and matrix multiplication. For instance, the dot product is used to calculate the similarity between two vectors, while matrix multiplication is used in neural networks to perform linear transformations between layers.**Machine Learning:**

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