Loose ends and Magnetic Fields in Astronomy. Exam tips – come to class! - Course Evaluations – come to class! - energy in fields - magnetism in matter - astronomical applications. Energy Density in EM Waves. The energy density, u , is the energy per unit volume
Recall these equations:I=Q/t
T=2πr/vL=mvrμ=IA (sub in the above, and A=πr2)Imagine a little circuit with an electron moving at a distance
r from the nucleus of an atom. Combining these, we can
This is the magnetic moment of anelectron
Now, because the angular momentum L for electrons isquantized, L=The smallest possible non-zero value of the magnetic
moment is :
Q: So, if all electrons have this unit of magnetic moment,
why are not all substances magnetic ???
Magnetic fields ‘rotate’ an electromagnetic wave. This is called Faraday Rotation, and it allows us to measure the magnetic field of interstellar space.
galaxy M51 and its
Studying the fields
helps us understand
how galaxies form and
evidence for a super
massive black hole at
the center of this
strong magnetic fields on
the surface of the sun.
We can detect them on other
simulation of the
reversal of earth’s
The earth’s magnetic field.
These are called MHD (magneto-hydro-dynamics simulations.