This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Slide 1
Chapter 30 Sources of Magnetic Field
Slide 2
Introduction This chapter will focus on the sources of magnetic
fields: moving charges. Well look at the field created by a current
carrying conductor, as well as other symmetrical current
distributions. Well look at the force between two current- carrying
conductors. Well finish by looking at the processes that result in
materials being naturally magnetic.
Slide 3
30.1 The Biot-Savart Law Shortly after Oersted discovers that a
compass needle is deflected by a nearby current- carrying conductor
(1819) Jean-Baptiste Biot and Felix Savart begin quantitative
experimentation. Their experimental results have given a
mathematical expression for the magnetic field at some point in
space in terms of the current that causes it.
Slide 4
30.1 We will summarize results of their experiment concerning
the magnetic field dB at a point P associated with a length element
ds on a wire carrying current I.
Slide 5
30.1 The results: The vector dB is perpendicular to both ds and
r. The magnitude of dB is inversely proportional to r 2, where r is
the distance from ds to point P. The magnitude of dB is
proportional to the current and to the magnitude of ds. The
magnitude of dB is proportional to sin , where is the angle between
ds and r.
Slide 6
30.1 The mathematical expression summarizng these observations
is known as the Biot-Savart Law: Remember o is the permeability of
free space Again, note that dB is only the field created by a
single element of the conductor and to find the total magnetic
field B at point P, we must integrate.
Slide 7
30.1 Integration gives We must be careful with this integration
as in does involved the vector cross product. For direction of the
B field, the right hand rule is used. Point thumb in direction of
I, curling fingers show the direction of B.
Slide 8
30.1 Quick Quiz p. 928 Example 30.1 Resulting Equations 30.2,
30.3
Slide 9
30.2 Magnetic Force between Two Parallel Conductors If we have
two current carrying wires, the B field caused by one current will
exert a force on the other. If the conductors are parallel to each
other, then the B field is perpendicular to the current.
Slide 10
30.2 The force on wire one from B-Field two is And assuming
long wires (