# Module 2d - News of the day Will post quiz marks this...

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2/5/2009 1 News of the day Will post quiz marks this afternoon on WebCT Today’s lecture is a mixture of reviews and very general concepts that I think will be helpful (essential?) in the next 3 modules. The slides are more informal (this material is best handled in textbooks) (Sadiku Chapters 1,2,3 for maths, 9 for Maxwells ’ equations). Early practice for Module 3 PA and Quiz: Examples 9-5 to 9-8 in Sadiku. Problems: 9-13 to 9-25. Module 2, lecture 4 Electromagnetic fields (part 1: introduction)

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2/5/2009 2 Physical origin and need for the existence of EM waves There is an electrostatic field EVERYWHERE around a charge, or charge distribution, up to “infinite” distances This field is vectorial (the force upon a test particule has a certain direction) If the source charge is moved, the direction of the force on the test charge must change, but it cannot do so instantaneously when the test charge is VERY far from the source Field vectors completely FILL space: we use a few field lines instead, for clarity Field lines follow the direction of field vectors at convenient points in space
2/5/2009 3 For instance, here are some representative field lines for a dipole source Field from a point source, when the point source changes location e- e- e- t=0 t= t1 Lines of force extending from sources in all directions. These lines indicate the direction of the force vectors associated with this source.

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2/5/2009 4 A snapshot in time t > t1 but less than d/l v l e- e- e- t=0 t= t1 The discontinuity in the lines of force must “travel” between the source and the test charge. Just like a transient on a transmission line! v
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Module 2d - News of the day Will post quiz marks this...

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