This document provides an overview of the basics of electotherapy and electrical components. It discusses the structure of atoms and molecules, conduction of electricity, different types of currents including faradic and galvanic, voltage, resistance, heat effects, self-inductance, eddy currents, and skin surface effects of high frequency currents. It also describes common electrical components like resistors, transformers, capacitors, and valves/triode valves and their functions.

1. BASICS OF
ELECTOTHERAPY
Prof. Ibrahim
ELBOGHDADY

2. 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).

3. 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 neutrons
2)- 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 )

4. proprieties of electrons:
1) electrification by friction
→ static electricity.
E.g. glass & silk
Static electricity is frictional
when rubbed together.
electricity; difficult to discharge
other than all-or-nothing
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.

5. 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

6. 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 Hz
Interrupted 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 ++)

7. 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.

8. 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.

9. The heat effect of DC
If 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 / R
Where:
I = Electrical Current (Amperes)
V = Voltage (Voltage)
R = Resistance (Ohms)
V
I R

10. 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) volt
and 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.

11. Self inductance:
changing current on the primary
coil induce electromagnetic field
in 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 Henry
when rate of change of current is 1 amp/sec
& back electromagnetic force equals 1 volt,
the self inductance of the coil equal 1 Henry.

12. 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 building
up the core from iron laminates
isolated from each other by thin
layer of laket therefore the resistance of this eddy current is greatly
increased. And the magnitude of current decreased.

13. 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.
11/18/2014 Mansoura rheumatology

14. 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 associated
magnetic filde moves out of wire as the current
increases and collapse back into the axis as the
current decreased to zero, thus line of filde cut
the conductor and back electromagnetic force
is induced, the innermost layers of the conductor
are 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 tubing
¼ inch in diameter.
In S.W. therapy this effect isn't imp. for current passing
through human body, since conductivity of tissue too low.

15. Basic Electrical Components

16. Resistor
A resistor is an electrical
component that limits or
regulates the flow of
electrical current in an
electronic circuit.
Transformers
A 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.

17. 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 = Microfarad
Capacitors 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 electrons
on the other plate (+ charge)

18. 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 condenser
2. Resistance of pathway
3. 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

19. 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 valve
Neutral: grid will not effect electron flow
Uses:
Rectification: as current flows in one direction it is possible to convert an AC to DC
Amplifier: triode valve can be used as electronic amplifier
Switch: triode valve can be used to break the circuit.