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BASICS OF 
ELECTOTHERAPY 
Prof. Ibrahim 
ELBOGHDADY
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 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 )
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.
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 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 ++)
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 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
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.
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.
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.
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
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.
Basic Electrical Components
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.
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)
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
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.

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Basics of elecrticity

  • 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.
  • 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.