This document is a lecture on vector algebra and electromagnetic field theory given by Prof. Dr. Magdi El-Saadawi to 2nd year electrical engineering students. It covers vector multiplication, including the dot and cross products. It also discusses the gradient of a scalar field, divergence of a vector, and the divergence theorem. Examples are provided to illustrate these concepts.
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Lec 02 2015 electromagnetic
1. Electromagnetic Field Theory
2nd Year EE Students
Prof. Dr. Magdi El-Saadawi
www.saadawi1.net
saadawi1@gmail.com
2014/2015
2. Chapter 1
VECTOR ALGEBRA
(Continue)
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3. 1.5. Vector Multiplication
Vectors may be multiplied by scalars: The magnitude of the vector changes, but its direction does not when the scalar is positive.
In case of vector multiplication:
the dot product (also called scalar product)
the cross product (also called vector product).
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4. 1.5.1 The dot Product
Two vectors and are said to be orthogonal (or perpendicular) with each other if 10/16/2014
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5. 1.5.1 The dot Product
The dot product obeys the following identities: 10/16/2014Prof. Dr. Magdi El-Saadawi5
6. 1.5.1 The dot Product
The most common applicationof the dot product is:
The mechanical work W, where a constant force F applied over a straight displacement L does an amount of work i.e.
Another example is the magnetic fields 陸, where
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7. 1.5.2 The cross product10/16/2014
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9. 1.5.2 The cross product
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10. 1.5.2 The cross product10/16/2014
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11. 1.5.2 The cross product10/16/2014
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12. 1.5.2 The cross product10/16/2014
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13. 1.6. The Gradient
The gradient of a scalar field is:
a vector field that lies in the direction for which the scalar field is changing most rapidly. The magnitude of the gradient is the greatest rate of change of the scalar field.(see figure 1.9 pp. 19) 10/16/2014Prof. Dr. Magdi El-Saadawi13
19. 1.7. Divergence of a vector and Divergence Theorem
The flux
Assume a vector field A, continuous in a region containing the smooth surface S, we define the surface integral of the flux of through S as:
Or
For a closed surface
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21. 1.7. Divergence of a vector and Divergence Theorem10/16/2014Prof. Dr. Magdi El-Saadawi21
22. If there are no sources within the boundary surface, thus the integral will get the value zero (Fig. b)
If there is a source (or sink) within the surface of integration, which generates new field lines the integral will get a value different from zero (Fig. a).
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24. 1.7. Divergence of a vector and Divergence Theorem
The theorem of Gauss(Divergence theorem) is proved from the definition of the divergence and it enables to transform surface integrals into volume integralsas follows:
The volume integral about a specific flux from an element of volume V is equal to the flux thorough going from the closed surface S bounding this volume (V).10/16/2014Prof. Dr. Magdi El-Saadawi24