BASICS OF ELECTOTHER

APY

Prof. IbrahimELBOGHDADY

Structure of matter:important considerations:

Atoms: are the smallest particles which retain physical and chemical propriety of element.

Element: composed of atoms, all atoms of same element are identical.

Molecule: formed of at least 2 atoms of same element, e.g.( H2 )

Compound: formed of at least 2 atoms of different elements, e.g. ( NO “Nitric oxide”).

Ion: an atom which has gain or lost a charge. atom gained an electron ( e-) → negative ion = anion.atom lost an electron ( e-) → positive ion = cation.

Crystals: Compound of ionic nature such as Nacl Kcl, dissociable in solution into corresponding ions: Na+ , K+ and Cl- ( when dissociated it conduct electricity through solutions).

Structure of atom:

1)- Nucleus: composed of proton (positive charge) and neutron (neutral). → atomic number = nb of proton → atomic mass = nb of protons + nb of neutrons2)- Outer structure: electrons orbits (shells) 7 shells at least: K → 2 electrons. L → 8 electrons. M → 18 electrons. …. etc

Number of electrons in shell = 2N2 ( N = the nb of shell )

proprieties of electrons:

1) electrification by friction → static electricity. E.g. glass & silk when rubbed together.

2) conduction of electricity on metals: metals have free electrons, these free electrons under effect of electromagnetic force cause flow of electronic current in diff. directions.

3) conduction of electricity through solution of electrolytes.

Static electricity is frictional electricity; difficult to discharge other than all-or-nothing

Current:passage of stream of electrons along a conductor. Current is measured in units called amperes.1 amp = one coulomb per second, or 6.241 × 1018 electrons/ sec.(The quantity of electricity is measured in coulombs.) Types of currents: faradic galvanic pulsed

Types of Current (comparison between faradic & galvanic):Faradic current (alternated , indirect) AC Galvanic current ( continuous , direct)DC

Direction

Biphasic with variable amplitude

V(velocity)=λ(wave length) x µ(freq.)

Constant in direction & amplitude

Duration Short < 1ms “ interrupted AC” Long 100ms “ interrupted DC”

Frequency

low intermediate high

1000 Hz 100,000 Hz(Hz = nb of cycles/sec)

30 – 100 Hz (most used in therapeutic.)

Low < 30 HzInterrupted direct current

on off

Source Dynamo (conversion of mechanical energy into electrical energy)

Batteries and accumulators (conversion of chemical energy into electrical energy)

Stimulation of Motor nerves

• Mainly ++ of innervated muscles • titanic contraction if > 50 Hz .• Non effect on denervated muscles.

+++ of denervated muscles, brisk contraction on make & on break.(surged c. +++ denervated ms. non effect on inn. ms.)

Stimulation of Sensory nerves

• Pricking sensation • VD (erythema).

• Burning sensation • Reflex VD ( sympa ++)

cont .. Types of Current:Faradic current Galvanic current

Indication

Electro diagnostic Ms. strengthening after (trauma, pain) Reeducation of Ms. after prolonged disuses. Education of new Ms function after tendon

transfer (as in flat foot). increase venous & lymph drainage.(edema) Decrease adhesion on scares. Hysterical conditions.

Electro diagnostic ++ of paralyzed Ms. Of LMNL. Peripheral nerve injury. Bell’s palsy. Iontophoresis. Hysterical conditions.

Voltage:Volt: is the unit of measurement for potential difference across a conductor.Resistance:electrical resistance is something that “resists” the flow of electrons/current.Electrical resistance is measured in Ohms (Ω). Resistivity: S(ohm/cm) x L(cm) / A (cm2) S= specific resistance.Conductivity (σ)= 1/Resistivity.========================================effects of direct current: *chemical effects: electrolytic effect “ ions migration” *heat effects: ohm’s low & joule's low “see later”. *magnetic effect: right hand rule of flaming.

The heat effect of DCIf a current is allowed to pass in an electric circuit the following characteristic will develop:electrical current(I) flowing in the circuit is proportional to the voltage (V) and inversely proportional to the resistance (R).Ohm's law:I = V / RWhere:I = Electrical Current (Amperes)V = Voltage (Voltage)R = Resistance (Ohms)

V

I R

When a current passes through a conductor some of its energy is converted to thermal energy.Heat produced (H) is proportional to:current in amperes (I)potential difference in(v) voltand the time in seconds (t)V=IR “ ohm’s low”

Joule’s low: HJ = Ix(IR) T (J= I2RT).

(J):mechanical equivalent of heat. (calorie* = 4.2joule).* Calorie: amount of heat needed to rise the temp. of 1gm of water one degree C between 14.5 – 15.5 C.

Self inductance: changing current on the primary coil induce electromagnetic fieldin itself opposing the change in current which produces it back electromagnetic force.Ratio of induced electromagnetic force to rate of change of current is called self inductance of the coil and measured in Henrywhen rate of change of current is 1 amp/sec& back electromagnetic force equals 1 volt, the self inductance of the coil equal 1 Henry.

Eddy currents:Def.: are the currents induced in any conductor by changing magnetic field.If the current in the coil is increased in one direction electromagnetic force is induced in the iron core which sets up current in the opposite direction.These current are circulating current in the solid conductors they can be reduced by buildingup the core from iron laminatesisolated from each other by thinlayer of laket therefore the resistance of this eddy current is greatlyincreased. And the magnitude of current decreased.

04/10/2023 Mansoura rheumatology

Eddy currents are utilized in short wave diathermy when high freq. current passed through electric cable wrapped around patient limb eddy current is induced heating it.

Skin surface effect of current:when current flow in cylindrical wire at high freq. it tend to confine itself to the outer layer “or skin” of the conductor effective area of the conductor is reduced & resistance is greater than value measured in the direct current circuit.Cause: for alternating H.F. current the associatedmagnetic filde moves out of wire as the current increases and collapse back into the axis as thecurrent decreased to zero, thus line of filde cutthe conductor and back electromagnetic force is induced, the innermost layers of the conductorare cut by all lines of force every time the field is established, but the outermost layers are cut by fewer lines of force. To reduce this effect the conductors of high freq. are made of copper tubing¼ inch in diameter.In S.W. therapy this effect isn't imp. for current passing through human body, since conductivity of tissue too low.

Basic Electrical Components

ResistorA resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit.

TransformersA transformer is an electrical apparatus designed to convert alternating current from one voltage to another. Transformer works on the principle of mutual induction of two coils. When current in the primary coil is changed, the flux linked to the secondary coil also changes. Consequently an EMF is induced in the secondary coil.

Capacitor (condensers)Capacitance is the ability of a device to store electrical energy in an electrostatic field. Or the ability of a component to store an electrical charge. The Symbol for Capacitance is “C”.Capacitance is measured in Farads (F). The Farad is too large for ordinary use so typically the Microfarad of the Pico farad are used. µF = MicrofaradCapacitors consist of two conducting surfaces separated by an insulator.When a capacitor is connected to a voltage source current will flow until the capacitor is fully charged. The capacitor is charged with an excess of electrons on one plate (-charge) and a deficiency of electronson the other plate (+ charge)

A capacitor discharges when the accumulated charge is allowed to flow off the plates.The time taken for this discharge depends upon 1. Capacitance of condenser2. Resistance of pathway3. Quantity of electricity

Capacitors, oscillator circuit: An oscillatory circuit is a condenser and an induction coil in low ohmic resistance.

Animated diagram showing the operation of a tuned circuit (LC circuit). The capacitor stores energy in its electric field E and the inductor stores energy in its magnetic field B (green). This jerky animation shows "snapshots" of the circuit at progressive points in the oscillation. The oscillations are slowed down; in an actual tuned circuit the charge oscillates back and forth tens of thousands to billions of times per second.http://en.wikipedia.org/wiki/LC_circuit

Valves:These are devices which allow electron flow in one direction only and working using heat.The cathode (filament) heated to produce space charge of electrons. (thermionic emission)The anode (plate) attracts electrons across the valve.Triode valve :by using an external circuit to make the grid – ve: repel electron to stop the flow+ ve: allows electron flow through valveNeutral: grid will not effect electron flowUses:Rectification: as current flows in one direction it is possible to convert an AC to DCAmplifier: triode valve can be used as electronic amplifierSwitch: triode valve can be used to break the circuit.