Electromagnetism

Running head: Electromagnetism 1

Electromagnetism 2
QUESTION ONE
Magnetic flux that is flowing in the electromagnet spreads out in the region around the sample
causing a bulging out of magnetic field lines, the spreading out of the field is what is called
fringing. The change in reluctance between the electromagnet and the sample causes a
discontinuity in magnetic flux which eventually causes fringing. The increased reluctance in the
sample to be specific causes fringing. Reluctance, on the other hand, relates to the relative
permeability μr, surface area S and thickness t of the sample by the formula below
R= t/μr*S
A reduction in reluctance will lead to a reduction in fringing effects and vice versa, so the
geometry of the sample relates to the fringing. The higher the thickness of the sample the higher
the fringing, and a thinner length of the sample results in a lesser fringing. With a large surface
area and relative permeability sample, less fringing is expected. If the surface area and the
relative permeability of the sample is smaller there would be larger fringing.
QUESTION TWO
Assumptions made in the calculations are
• leakage flux is negligible
• the fringing effect is negligible
• the uniform cross-sectional area of the sample throughout its length
• an electromagnetic core is represented by a single loop of the magnetic circuit
magnetomotive force F created by the electromagnet is directly proportional to the number of
turns, N and the current, I flowing in the circuit, and is given by the formula below
F=N*I, number of turns is 500turns and the current I is 0.1A
=500*0.1
= 50 ampere-turns
Ampere’s law states that
N*I=H*L...........................................................1
L represents the total length of the magnetic circuit path and is made up of L core present in the
core and L sample in the sample.
L=L core + L sample................................................2
Substituting 2 into 1
N*I = (H core*L core) + (H core*L sample) ........................3