Where is the magnetic field strongest?

School blocks YouTube? Use file below.

| Magnetic_Field_Lines.mov |

St. Mary's U. Astronomy & Physics Dept.






B) Magnetic Fields - regions in space where a magnetic forces may be detected



David Colarusso, Youtube



We will focus on fields around:


1) current carrying wire


2) permanent & electromagnets


3) Bar Magnets




Magnetic lines of force of a bar magnet shown by iron filings on paper:Magnet from
 Practical Physics, publ. 1914 by Macmillan and Company - copyright expired



(Actual magnetic fields contain
many more lines of magnetism)





Solar Flames are deflected by
 the suns magnetic field 




1. Magnetic flux lines - lines of magnetism in a magnetic field.

- magnetic field is not continuous.


Between each line of magnetism
there exists ....


... no magnetic field




a) The needles of a compass line up perfectly with the flux lines





b) The arrows on a flux line show where the North Pole of a compass would point in that field.





Source Unknown



Compass / Bar Magnet
Windows to the Universe




Flux Arrows point


and back over again to North




[ Flash ]


c) Magnetic force strongest at the ...




At Poles ...


  ... where flux lines are closest.



Cutting Magnets ...


... each piece is a brand new magnet





How can magnets

attract non-magnets?

St. Mary's Physics YouTube Channel


Directions: Slide the magnet on the right over to the metal on the left. (unmagnetized metal on left)

[ Flash ]

Certain metals contain magnetic regions called domains.
They are randomly orientated.






The magnetic field in the bar magnet reorient the random magnet domains in the metal




Ex) Which diagram best represents magnetic flux lines around a bar magnet?


August 2002 Regents 



Flux lines don't cross, Out of North into South







d) Measuring the strength of a magnetic field


Put a wire with a known current into the field and measure the force on the wire



Where does the north pole
 of a compass point south? 

Earth's Magnetic Field
Windows to the Universe




What are these magnetic lines called?

Where is the field strongest?

Mina Gong - Class of 2009







Flux lines, The field is strongest at the poles



Flux Lines - Wire



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