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

Magnetic fields throughout the Universe

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 COMA CONSTELLATION

Pretty much each dot here is a galaxy

Magnetars

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 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)

have the STRONGEST magneticfields in the Universe

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]

Image: NASA SDO/Lockheed Martin Space Systems Company

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.

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 bullet-shaped 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 fieldhas been weakening over the past 180 years or so

Close up, the field

looks like thatof 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).

Lodestone at the Smithsonian Institute

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.

Magnetic ores

The name magnet may come from lodestones found in the ancient Greek city of Magnesia.

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 alphabetAlpha 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 (one-

tenth) 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 i2 – II or ii3 – III or iii4 – IV or iv5 – V or v6 – VI or vi7 – VII or vii 8 – VIII or viii9 – IX or ix10 – X or x11 – XI or xi12 – XII or xii13 – XIII or xiii14 – XIV or xiv15 – XV or xv16 – XVI or xvi17 – XVII or xvii18 – XVIII or xviii19 – XIX or xix 20 – XX or xx

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