# lecture20 - Sources of Magnetic Fields Sources Be s m tic...

This preview shows pages 1–14. Sign up to view the full content.

Sources of Magnetic Fields Sources of Magnetic Fields

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Besides magnetic poles, electric currents create magnetic fields. There are two ways of calculating B produced by currents: i) Biot-Savart Law : Field of a “current element” (analogous to a point charge in electrostatics). i) Ampère’s Law : An integral theorem similar to Gauss’s law.
m/A T 10 4 7 o × = - π μ ˆ 4 2 o r I r ds dB × = We get the total B by integrating ds along the wire : (“permeability of vacuum”) I I θ ds dB ˆ 4 2 o × = r I r ds B Biot-Savart Law Biot-Savart Law

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Quiz When is d B =0 ? How does d B vary with r ? Current I in a straight wire What is the direction of B at points a and b ? a b
Example 1 Example 1 Find B at a distance R from a long straight wire x y I R φ dx dB θ i ds ˆ = dx direction) - z (in o dx r I dB 2 sin 4 θ π μ = (note sin = R/r = cos θ ) r

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Solution
Result : the magnitude of the field produced at a distance R from a long straight wire is: R I B π μ 2 0 = I The field lines form circles around the wire. Note the right-hand rule.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 01/13/2011 for the course PHYSICS Physics 1E taught by Professor Venus during the Winter '03 term at McMaster University.

### Page1 / 14

lecture20 - Sources of Magnetic Fields Sources Be s m tic...

This preview shows document pages 1 - 14. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online