Transcript Electrical & Electronic Principles

Electrical and Electronic
Principles
BTEC National Diploma
O
Introduction
Magnetism Assessment Criteria
P7. describe the characteristics of a magnetic field.
P8. describe the relationship between flux density (B)
& field strength (H).
P9. describe the principles & applications of
electromagnetic induction.
D1. analyse the operation and the effects of varying
component parameters of a power supply circuit that
includes a transformer, diodes and capacitors.
Know the principles and properties of
magnetism: content
Magnetic field:
• Magnetic field patterns eg
flux, flux density (B),
magnetomotive force (mmf)
and field strength (H),
permeability, B/H curves
and loops;
• Ferromagnetic materials;
reluctance; magnetic
screening; hysteresis
Electromagnetic induction:
• Principles eg induced
electromotive force (emf),
eddy currents, self and
mutual inductance;
• Applications (electric
motor/generator eg series
and shunt motor/generator;
transformer eg primary and
secondary current and
voltage ratios);
• Application of Faraday’s and
Lenz’s laws
THE COMA CONSTELLATION
Pretty
much
each
dot
here is
a galaxy
 Almost all white blobs on the left hand optical image of the
constellation Coma are – not stars – but whole galaxies (each of
which contains billions of stars).
 The radio image on the right of the same part of space gives an
indication of the distribution of the magnetic fields in the regions
of space between the galaxies.
Images: (1) ESO; (2) H. Lesch, USM
The interior field of SGR 0418+5729
(above) is about a trillion (1012)
tesla, one of the strongest
magnetic fields in the known
Universe – here shown bursting
of the star’s surface in the form of
a loop.
(Image: ESA/ATG Medialab)
About one tenth of neutron stars
are magnetars. Their magnetic
fields are a hundred million times
greater than the of the strongest
man-made magnet
(a neodymium-based, rare-earth
magnet has a field of about 1 tesla).
Weird things happen in these
immense magnetic fields. For
example, a hydrogen atom deforms
into a spindle 200 times narrower
than its normal diameter.
The magnetic fields of our galaxy, the
Milky Way
The main magnetic field
structure lies in the plane
of the disc and follows the
spiral arms.
 The red arrows are in the opposite
direction to the black ones – i.e. the
magnetic field is reversed.
 There is also a toroidal and a
poloidal magnetic field (not shown)
The Sun’s magnetic
field lines.
[August 2010]
The dark areas are
coronal holes from
which lots of field
lines whip out into
space. The corona is
the outmost layer of
the sun.
Image: NASA SDO/Lockheed
Martin Space Systems Company
The heliosphere is not exactly a sphere!
Part of the heliosphere: more detail
Solar System cutting through Milky Way’s magnetic field
This graphic depicts the Solar
System, encased in a bulletshaped envelope of charged
particles (yellow), as it
streaks through the
interstellar magnetic field of
the Milky Way galaxy (brown
lines) at about 62,000 miles
an hour.
Image courtesy Opher et al., 2007/Science
The Earth’s magnetic field
has been weakening over the past 180 years or so
Close up,
the field
looks like that
of a bar magnet
The Earth’s internal structure
Moon-sized SOLID
iron-nickel inner
core superrotating
eastwards.
MOLTEN iron-nickel outer core rotating
westwards. Moving charged particles
such as eg free electrons instigate the
magnetic field.
Earth’s magnetic field viewed from
further out
As it orbits the Sun, the Earth’s magnetic field DISTORTS as it ‘pushes against’ the
Sun’s solar wind (which follows the direction of the Sun’s own magnetic field).
Magnetic ores
A lodestone is a naturally magnetized
piece of magnetite. It is by far the most
magnetic of all minerals. Lodestones –
from the Saxon loeden,“meaning leading
or directing - were used as the first
magnetic compasses.
The name magnet may
come from lodestones
found in the ancient Greek
city of Magnesia.
Lodestone at the Smithsonian Institute
Animal magnetism
Theories as to how birds such as pigeons
navigate using the Earth’s magnetic field refer
to inbuilt compasses in the ears, the eyes, the
beak or the brain.
‘Magnetotactic’ bacteria orient
themselves and move along Earth’s
magnetic field lines.
The cosmological origin of electromagnetism
• According to theory, immediately after the
Big Bang, there was only one super-force.
• This super-force split in stages into four
separate fundamental forces (interactions).
• Electromagnetism is one of these four, the
other three being gravitation, the strong
nuclear interaction and the weak nuclear
interaction.
• Electromagnetism includes both electricity
and magnetism as elements of one
phenomenon. Electricity and magnetism are
linked.
Greek alphabet
Alpha
Beta
Gamma
Delta
Epsilon
Zeta
Eta
Theta
Iota
Kappa
Lambda
Mu
Nu
Xi
Omicron
Pi
Rho
Sigma
Tau
Upsilon
Phi
Chi
Psi
Omega
















































Roman numerals
• The letters should be arranged from the one with the largest
value to the one with the smallest.
• Each letter's value is added to the previous ones.
• Only powers of ten (I, X, C, M) can be repeated.
• Do not repeat any letter more than three times in a row.
• Because of the preceding rule, certain numbers must be
written using subtraction. In this case, a letter with a smaller
value precedes one with a larger value and the value of the
smaller is subtracted from the larger. The result is then added
to the rest of the letters.
The following rules apply to subtraction:
• Only powers of ten (I, X, C, M) can be subtracted.
• The smaller letter must be 1/5th (one-fifth) or 1/10th (onetenth) the larger one.
• The smaller letter must be either the first letter or preceded by
a letter at least ten times greater than it.
• If another letter follows the larger one, it must be smaller than
the number preceding the larger one.
1 – I or i
2 – II or ii
3 – III or iii
4 – IV or iv
5 – V or v
6 – VI or vi
7 – VII or vii
8 – VIII or viii
9 – IX or ix
10 – X or x
11 – XI or xi
12 – XII or xii
13 – XIII or xiii
14 – XIV or xiv
15 – XV or xv
16 – XVI or xvi
17 – XVII or xvii
18 – XVIII or xviii
19 – XIX or xix
20 – XX or xx
End