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THEORIES OF MAGNETISM

Muhammad Iqbal

JCN

Integrated Sciences-II (Physics) Unit-IV

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Weber's Theory

A popular theory of magnetism considers the molecular alignment of the material.

This is known as Weber's theory. This

theory assumes that all magnetic

substances are composed of tiny

molecular magnets. Any unmagnetized

material has the magnetic forces of its

molecular magnets neutralized by adjacent

molecular magnets, thereby eliminating

any magnetic effect.

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A magnetized material will have most of its

molecular magnets lined up so that the

north pole of each molecule points in one

direction, and the south pole faces the

opposite direction.

A material with its molecules thus aligned

will then have one effective north pole, and

one effective south pole. where a steel bar

is magnetized by stroking.

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When a steel bar is stroked several times in the same direction by a magnet, the

magnetic force from the north pole of the

magnet causes the molecules to align

themselves.

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Domain Theory

A more modern theory of magnetism is based

on the electron spin principle. From the study

of atomic structure it is known that all matter is

composed of vast quantities of atoms, each

atom containing one or more orbital electrons.

The electrons are considered to orbit in

various shells and sub shells depending upon

their distance from the nucleus.

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The structure of the atom has previously been compared to the solar system, wherein the

electrons orbiting the nucleus correspond to the

planets orbiting the sun. Along with its orbital

motion about the sun, each planet also revolves

on its axis. It is believed that the electron also

revolves on its axis as it orbits the nucleus of an

atom.

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The effectiveness of the magnetic field of an atom is determined by the number of electrons

spinning in each direction. If an atom has equal

numbers of electrons spinning in opposite

directions, the magnetic fields surrounding the

electrons cancel one another, and the atom is

unmagnetized. However, if more electrons spin

in one direction than another, the atom is

magnetized. It has been experimentally proven

that an electron has a magnetic field about it

along with an electric field.

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An atom with an atomic number of 26, such as iron, has 26 protons in the nucleus and 26

revolving electrons orbiting its nucleus. If 13

electrons are spinning in a clockwise direction

and 13 electrons are spinning in a

counterclockwise direction, the opposing

magnetic fields will be neutralized. When more

than 13 electrons spin in either direction, the

atom is magnetized.

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Domain Magnetic Theory of

Electron Spin

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Application of Magnetism in

Nursing

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Magnetic Resonance Image

Advantages

Non-invasive

No ionizing radiation

Repeat studies present no problem

Disadvantages

Potential for accidents and even fatalities

Damage to equipment / cost

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Static magnetic field biological effects mechanical effects auditory damage Other issues contrast agents critically ill patients/resuscitation

monitoring

claustrophobia

Safety issues

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Static magnetic field

Measured in Gauss or Tesla (10,000G equivalent to 1T)

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Static Magnetic Fields

1. Biological effects (potential risk) - Exposure to static magnetic fields of up to 4T are not

thought to be harmful

- Distorted ECG (magnetohydrodynamic effect)

- Be careful with pregnancy.

2. Mechanical effects (very real risk)

- translational or attractive forces on metallic objects when brought into the field

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Mechanical effects

Projectile or missile effect - the attractive forces exerted by the static magnetic field present the greatest potential for patient injury - objects will be pulled out of hands, pockets etc, and fly into magnet which has caused injury and death.

Effect on ferromagnetic implants

- electro-mechanical eg pacemakers

- biomedical eg valves, stents

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What is typically ferromagnetic? EQUIPMENT PERSONAL ITEMS (leave outside)

Oxygen cylinders Keys, pens

Wheelchairs Bleeps (page, buzz, etc.)

Trolleys Mobile phones

IV stands Coins

Monitoring equipment Stethoscopes

Ventilators Scissors

It is easy to forget objects, particularly when responding to an emergency!

Remember also magnetic strips will be wiped (credit cards)

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Warnings to minimize accidents?

OUTSIDE THE SCANNER ROOM

Signage

Barrier cords to scanner room

Restricted access - swipe card / coded entry

system

INSIDE Health Care Workers

Should not remain in the room when scanner is operational,

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Never be complacent accidents do happen!

Oxygen cylinder Infusion pump

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Cerebral aneurysm clips

Metallic foreign body in the eye

Bullets (gun shot)

Ocular implants (containing metal)

Swan-Ganz

Contraindications to CMR*

Implants & metal Electromechanical implants

Pacemakers

Pacing wires

Cochlear implants

Hydrocephalus shunts

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Nursing Responsibility: Safety Checklist

Removal of accessories - watch, jewellery hearing aids, glasses, false teeth, artificial limbs and prostheses

Removal of clothes containing metal eg zips

Educating patient having invasive devices is important

Important to know

Previous heart surgery?

Asthmatic or allergies?

(in relation to contrast)

Tattoos or permanent eye

liner

Essential to know

Cardiac pacemaker? Previous neurosurgery?

Implants or metal in the body?

Pregnant (prudent approach)?

Drug patch with foil backing?

Essential preparation

Nurses need to assess the patient on the following checklist

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Factors to reduce anxiety

Education and explanation

Trial visit to the department

Maintaining physical and verbal contact

Presence of a relative or friend

Good communication system

Alarm

Good light and ventilation

Music

Pleasant thoughts

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This could be you!