Basic electricity

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Electrotherapy

Basic Electricity

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What is electrotherapy?

Medical therapy using electric currents. Also

called electrotherapeutics.

Electrotherapy, also electro physical agents

(EPA) are any forms of treatment or

assessment conducted using an electro

physical agent which can be applied externally

to the human body.

http://www.thefreedictionary.com/electrotherapy

Robertson V, Ward A, Low J, Reed A. Electrotherapy Explained. 4th edition. Elsevier; 2006. p. 2

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Atom

http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/static_elec/staticrev1.shtml

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Atom

Electrons fill the lowest energy shells

Atoms tend to have their outer shell full

They may gain or loose electron to achieve this.

If the atom gains an electron it is negative ion.

(Cl-)

If the atom loses an electron it is positive ion.

(Na+)

Forster A, Palastanga N. Clayton’s Electotherapy, Theory ans Practic. 9th Ed. W B Saunders; 2006. p 2

http://198.185.178.104/iss/electricity/pages/b11.xml

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Atom

Atoms can have an electrical charge, positive or negative.

This happens when an atom gains or loses electrons.

The number of protons never changes in an atom.

More electrons means a negative charge and fewer means a

positive charge.

Once an atom has an electrical charge it is called an ion.

In an ion the atomic number and atomic mass do not change

from the original.

If an atom were to gain or lose neutrons it becomes an

isotope.

http://www.universetoday.com/56747/atom-structure/#ixzz2dT7JQkrm

http://revisionworld.co.uk/quick-revise/5133

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Chemical bond

A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms.

The bond is caused by the electrostatic force of attraction between opposite charges, between electrons and nuclei.

The number of electrons in the outer shell of an atom has the effect on the reactions of that atom with others.

Inert gases like argon, krypton have complete outer shell.

Reactive gases are those elements are looking to complete their outer shell so they are reactive.

http://en.wikipedia.org/wiki/Chemical_bond


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Compounds

A compound is a substance formed by the union of two or more elements

They can be separated into simpler substances by chemical reactions.

They have a unique and defined chemical structure;

They consist of a fixed ratio of atoms

Chemical compounds can be;

molecular compounds held together by covalent bonds,

salts held together by ionic bonds/ electrovalent,


http://en.wikipedia.org/wiki/Chemical_compound

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Covalent Bonds

A form of chemical bonding

between two atoms which is

characterized by the sharing of

pairs of electrons between atoms.

A covalent bond is formed

between two non-metals that

have similar electro negativities.

Neither atom is "strong" enough

to attract electrons from the other.

For stabilization, they share their

electrons from outer molecular

orbit with others.http://www.diffen.com/difference/Covalent_Bonds_vs_Ionic_Bonds

http://facstaff.gpc.edu/~pgore/PhysicalScience/Naming-chemical-compounds.html

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Electrovalent Bonds

Also known as Ionic bond.

formed from the electrostatic attraction between oppositely charged ions in a chemical compound.

occur mainly between a metallic and a non metallic atom.

Non-metals (-ve ion) are "stronger" than the metal (+veion) and can get electrons very easily from the metal.

These two opposite ions attract each other and form the ionic bond.

http://www.diffen.com/difference/Covalent_Bonds_vs_Ionic_Bonds

http://facstaff.gpc.edu/~pgore/PhysicalScience/Naming-chemical-compounds.html

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Covalent Bonds vs. Electrovalent Bonds

Covalent Bonds.. Electrovalent Bonds..

are formed by mutual sharing of electrons are formed by complete transfer of

electrons

are made up of molecules. are made up of ions.

are usually liquids or gases. are hard, crystalline solids

are insoluble in polar solvents like water. are usually soluble in water.

are soluble in non-polar solvents like

benzene or carbon tetrachloride

insoluble in non-polar solvents like CI4.

generally have low melting and boiling

points.

generally have high melting and boiling

points

are bad conductors of electricity. are good conductors of electricity in the

molten state and in aqueous solutions

but insulators in the solid state.

http://www.publishyourarticles.net/knowledge-hub/science/what-is-the-difference-between-electrovalent-and-

covalent-compounds.html

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Static Electricity?

A stationary electrical charge that is built up on the surface of a material

After being rubbed, a plastic ruler can attract paper scraps.

Ruler carries electric charge.

It exerts electric force on paper

The interaction between static electric charges is called electrostatics.

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Insulators and conductors

In a conductor, electric current can flow freely,

in an insulator it cannot.

"Conductor" implies that the outer electrons of

the atoms are loosely bound and free to move

through the material.

Most atoms hold on to their electrons tightly

and are insulators.

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Insulators: materials that do NOT allow

electrons to flow through them easily.

Insulators can be easily charged by friction as the extra

electrons gained CANNOT easily escape.

Static Electricity ppt

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Conductors: materials that allow electrons to flow

through them easily.

Conductors CANNOT be easily charged by friction as

the extra electrons gained can easily escape.


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++ + +

+

metal can ---

--

----- --

induced

charges attraction

repulsion

Induction

• The production of a charge in

an uncharged body by

bringing a charged object

close to it.

When negatively charged rod is

put near a metal can...

• electrons of the can are

pushed away from the rod.

• top of the can: positive

• buttom of the can: negative

• So there is attraction >

repulsion


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Induction

----- --

paper +–+–+–+–

+–+–+–+–

attraction

repulsion

• Similarly, when

charged rod is close

to paper scrap...

• molecules of paper

align

• attraction between the

rod and + charge

• repulsion between the

rod and - charge


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Electric Fields

They are nothing but a way of pictorially mapping the electric field around a configuration of charges.

General Properties of Electric Lines of Force

The lines of force or field lines

1. start from positive charges and end at negative charges. In the case of a single charge, they may start or end at infinity.

2. two field lines can never intersect each other.

3. contract longitudinally.

4. exert lateral pressure on one another.

5. are perpendicular to the surface of a charged conductor.

6. do not pass though the conductor.

http://www.tutorvista.com/content/physics/physics-iv/electric-charges/electric-field-lines.php

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Electric Fields

If it is a positively charged body, then the

electric lines of force are directed away from

the body.

If the body is negatively charged, then the

lines of force are directed towards the body.


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Electric Fields

When two positively charged bodies are

involved, the electric lines of force gives a

vivid picture of mutual repulsion.

In the case of two equal and opposite charges,

the lines of force clearly shows mutual

attraction, the lines move from +ve to -ve.


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Electrical Current

http://www.howequipmentworks.com/physics/electricity/basic_electricity/basic_electricity.html

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Electrical Current

Current

Voltage

Resistance

http://www.reprise.com/host/electricity/voltage.asp

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Current

amount of electric

charge passing a point in

an electric circuit per unit

time

Current is measured in

units called amperes.

6.241 × 1018 electrons, or

one coulomb per second.

The quantity of electricity

is measured in coulombs.


http://en.wikipedia.org/wiki/Ampere

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In medical electricity the unit of current is in

milliamperes i.e. 1/1000 of an ampere


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Voltage

potential difference

across a conductor when

a current of one ampere

dissipates one watt of

power.

The unit of

measurement for

potential difference is

"volt".


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Resistance

electrical resistance is something that “resists” the flow of electrons/current.

Electrical resistance is measured in Ohms (Ω).

Most circuits have more than one component, called a resistor

A measure of this limit on charge flow is called resistance


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Resistance; Ohm's law

Ohm's law states that the

electrical current (I)

flowing in a circuit is

proportional to the voltage

(V) and inversely

proportional to the

resistance (R).

I = V / R

Where:

I = Electrical Current (Amperes)

V = Voltage (Voltage)

R = Resistance (Ohms)

http://inspectapedia.com/electric/ElectricalDefinitions.htm#Resistance

http://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/currentflow.htm

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http://www.howequipmentworks.com/physics/electricity/basic_electricity/basic_electricity.html#ohm_law

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Resistance

The simplest combinations

of resistors are the

a) series and

b) parallel

http://cnx.org/content/m42356/latest/?collection=col11406/latest

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Series Circuits

A series circuit is a circuit in which resistors are arranged in a chain

so the current has only one path to take.

equivalent resistance of resistors in series :

R = R1 + R2 + R3 + ...

The current is the same through each resistor but

Voltage changes on each resistor

http://physics.bu.edu/py106/notes/Circuits.html

http://cie-wc.edu/Series-and-Parallel-Circuits-4-11-11.pdf

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Parallel circuits

In a parallel circuit the resistors are arranged with their heads connected together, and their tails connected together.

equivalent resistance of resistors in parallel :

1/R=1/R1+1/R2+1/R3.....

The current in a parallel circuit breaks up but

The voltage across each resistor in parallel is the same.

1

0.2+0.0714+0.0476+0.04+0.01 = 2.7 Ω

http://cie-wc.edu/Series-and-Parallel-Circuits-4-11-11.pdf

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Electrical Watts

Watts is a measure of the amount of electricity being

used - a rate of electrical power consumption.

power (Watts) = current (amps) x potential

difference (volts)

For a current of 5 A and the potential difference of 12

V, the power is 5 × 12 = 60 W.

This means that 60 J of energy is transferred per

second.

http://inspectapedia.com/electric/ElectricalDefinitions.htm#Watts

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/electricity/mainselectrev4.shtml

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Joule’s law

When a current passes through a conductor some of its energy is converted to thermal energy.

Joule’s law states that the amount of heat produced in a conductor is proportional to the square of the current in amperes (I2), the resistance in ohms (R) and the time in seconds (t) for which the current flows. i.e.

Q = I2 Rt


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Basic Electrical Components

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Resistor

A resistor is an electrical

component that limits or

regulates the flow of

electrical current in an

electronic circuit.

http://searchcio-midmarket.techtarget.com/definition/resistor

http://www.mikroe.com/old/books/keu/01.htm

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Transformers

A transformer is an electrical apparatus

designed to convert alternating current from

one voltage to another.

The functions of Transformers are;

To alter the voltage of an alternating

current

To render the current earth free

http://www.acmepowerdist.com/pdf/Page_6-16.pdf


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Transformers, Working

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.

Upadhyay D . Electrical & Electronics Engineering. Hindustan college of Science & Technology. Ppt presentation

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Transformers; Construction

The core, which provides a path for the magnetic lines of flux.

The primary winding, which receives energy from the AC source.

The secondary winding, which receives energy from the primary winding and delivers it to the load.

The enclosure, which protects the above components from dirt, moisture, and mechanical damage.

http://www.navymars.org/national/training/nmo_courses/NMO2/module2/14174_ch5.pdf

http://www.emt-india.net/process/power_plants/Transformers.htm

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Transformers; Construction

Mainly Transformers have two

types of construction….

CORE type: the primary and secondary windings are placed on each side of the core.

The core type has two limbs

SHELL type: the LV & HV windings are sandwiched between each other.

shell type has three limbs.


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Transformers, Types

Step-up transformer Step-down transformer

http://keywon.com/wiki/index.php?title=AC_Circuits

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Transformers, Configurations

Static transformer

Variable transformer

Auto transformerhttp://keywon.com/wiki/index.php?title=AC_Circuits

http://www.cybermike.net/reference/liec_book/AC/AC_9.html

http://en.wikipedia.org/wiki/File:Tapped_autotransformer.svg

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Transformers, in Earthing

Using power without an isolating

transformer: Touching the live terminal

will result in a shock as the body

completes a circuit between live and

earth.

Using power with an isolating

transformer: Bridging between either

terminal and ground is safe because there

is no circuit through which the current

can flow.

http://www.soundonsound.com/sos/nov06/articles/crosstalk_1106.htm

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Capacitor

What is Capacitance?

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”

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&ved=0CGIQFjAH&url=http%3A%2F%2Fwww.

hamptonhigh.ca%2Fhaas%2Fdocuments%2Fintro%2FCapacitors.ppt&ei=RgYuUpjYNcLWrQfb9IGoDw&usg=AFQjCNFzJkiINpxX

A1epNOtoJ8FhQcaO8g&sig2=fUpX1eYhXN5TWWr11HrtGg

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Capacitor

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

pF = Picofarad

1 µµµµF = 0.000,001F

1 pF = 0.000,000,000,001F

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&ved=0CGIQFjAH&url=http%3A%2F%2Fwww.

hamptonhigh.ca%2Fhaas%2Fdocuments%2Fintro%2FCapacitors.ppt&ei=RgYuUpjYNcLWrQfb9IGoDw&usg=AFQjCNFzJkiINpxX

A1epNOtoJ8FhQcaO8g&sig2=fUpX1eYhXN5TWWr11HrtGg

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Capacitor

Also referred to as

a Condenser

It is a device for storing

electric charge.

Capacitors consist of

two conducting surfaces

separated by an

insulator.

http://www.electronics-tutorials.ws/capacitor/cap_1.html

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Capacitors,working

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


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Capacitors, electric field

The EF between the

plates of a charged

capacitor tend to take

the shortest route.

They repel one another

They rarely travel on

straight line


http://commons.wikimedia.org/wiki/File:VFPt_capacitor.svg

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Capacitors, oscillator circuit

An oscillatory circuit is

that of a condenser and

an induction coil in low

ohmic resistance.

Forster A, Palastanga N. Clayton’s Electotherapy, Theory ans Practic. 9th Ed. W B Saunders; 2006. p 35-36

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Capacitors, oscillator circuit

http://en.wikipedia.org/wiki/File:Tuned_circuit_animation_3.gif

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Capacitors, Types

Fixed Capacitors

the capacitance cannot be changed.

Variable Capacitors

the capacitance can be changed.

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Capacitors, Types

Fixed Capacitors

Electrolytic

Electrostatic

Mica

Ceramic

paper

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Capacitors, Types

Variable Capacitors

air capacitors

trimmers

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Thermionic valves

These are devices which allow electron flow in one direction only and working using heat.

The cathode (filament) heated o produce space charge of electrons.

The anode (plate) attracts electrons across the valve.


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Thermionic valves

Triode valve

It is possible, 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


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Thermionic valves

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 braek the

circuit.


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Thermionic valves

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Semiconductors

They are usually metals with the addition of impurities have electrons free to conduct current

n – type with excess of electrons

p – type with deficiency of electrons so + ve ‘holes’

If a p- and n- type semiconductors are fused together current can only flow in n to p direction

i.e. it acts as a valve

Forster A, Palastanga N. Clayton’s Electotherapy, Theory ans Practic. 9th Ed. W B Saunders; 2006. p37

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Semiconductors

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Transistors

Device that uses a small amount of current to control a large amount of current (Current Amplifier).

They utilize a sandwich of p- and n- type semiconductor materials.

Electron enters at emitter

current amplified and passed across through base

Electron leaves form collector


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Transistors

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Rheostat

Devices used to regulate current by altering

either the resistance of the circuit or

the potential in part of the circuit

Forster A, Palastanga N. Clayton’s Electrotherapy, Theory and Practice. 9th Ed. W B Saunders; 2006. p 39-40

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Rheostat

Construction

It consists of a coil of high

resistance wire wound onto

an insulating block with

each turn insulated from

adjacent turns.

Contact is made via a strip

from which insulation is

removed.

The contact is mounted on

a sliding bar or rotation

knob.Forster A, Palastanga N. Clayton’s Electrotherapy, Theory and Practice. 9th Ed. W B Saunders; 2006. p 39-40

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Rheostat

Variable or series rheostat

If all the coils of wire in

rheostat are included in

the circuit resistance is

maximum and current

lowest

Used in regulating heat in

apparatuses like paraffin

wax baths


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Rheostat

Potentiometer or shunt rheostat

Wired across a source of potential difference in parallel.

According to ohm's law greater the PD across the a resistance the greater the current produced.

When B at A no PD, so no current

When B at C maximum PD as in A

A current regulating mechanism


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General structure of LF generators

Low J, Reed A. Electrotherapy Explained, Principles and practice. 2 edition. Page 19

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Mains supply

Current for this is produced by dynamos (electrical generator) at power stations.

An EMF is induced by the movement of a conductor and two magnetic field in relation to each other.

Dynamos can produce either AC or DC

http://aaenvironment.com/Electricity.htm


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Mains supply

Advantages of AC

A greater voltage can be produced

Possible to alter voltage with static

transformers

So suitable for long distance transmission


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Mains supply, The grid system

Residential power supplied in India is two wire 220 volts, permitted variation 6%, and maximum load 40 amperes. Frequency 50 Hz.

A three phase current is generated.

i.e. three coils of dynamo generate three separate current.

Distribution of current via three live cables with a common neutral cable.

These four cables carry current across the country.

http://en.wikipedia.org/wiki/Mains_electricity_by_country


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Mains supply

http://en.wikipedia.org/wiki/File:Electricity_grid_simple-_North_America.svg

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Mains supply, wiring in house

Distribution to customer is by one live wire

and one neutral wire

It passes through main fuses, meter, main

switch and to various circuits in parallel.

The light circuits have 5 ampere fuses for

each 4 to 6 points

The power circuit with stronger wiring with

15 ampere fuse for each point.

Forster A, Palastanga N. Clayton’s Electrotherapy, Theory and Practice. 9th Ed. W B Saunders; 2006. p 43

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Fuse

It is designed to be a weak point in a circuit which ‘blows’ if a current of too great intensity is passed.

This causes the circuit to break

It consists of a wire of low melting point.

It is an safety feature.


Metal cap

To mains live wire

To neutral wire

Glass tube

Silver fuse wire

Metal cap

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Fuse

In Physiotherapy department a Fuse is an

essential safety feature.

They are included in the

department wiring and

electrotherapeutic equipments

If a fuse blows, the apparatus which causes the

damage should be disconnected and the main

supply switch off.


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Power plug

Three pin plug most common

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Earthing of apparatus

Precaution against earth shock

Earthing the device casing with a low

resistance wire.

In the event of device casing comes in contact

with exposed live wire the operator can receive

a shock.

However earthing the casing causes the current

to leak through and causes the fuse to blow.


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Electric shock

A shock is a painful stimulation of sensory nerves caused by a sudden flow, cessation or variation in the current passing through the body.

Severity of shock depends on

the magnitude of the current and

The path taken by the current.

Path taken through head, neck, heart or whole body might prove fatal.

Shocks are more sever with AC than DC.


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Electric shock, effects

A minor shock leads to fright and distress.

A severe shock can lead to;

Fall in BP

Loss of consciousness

Respiratory failure: signs of cessation of respiration, cyanosis

Cardiac arrest: signs of absent/abnormal breathing, absence of pulse and fully dilated pupils


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Electric shock, treatment

Following minor shock

Disconnect the victim from source.

Switch off current.

reassure the patient and allow to rest.

Give cold water to drink. (avoid hot water as it

can cause vasodilation and sweating leading to

fall in BP)


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Electric shock, treatment

Following severe shock

Victim is laid flat and allow easy breathing

Loosen tight clothing

Provide adequate ventilation

If the patient is unconscious summon MO.

If cessation of breathing give mouth to mouth, mouth to nose or O2 by bag and mask

In the event of cardiac arrest cardiac message must be added along with above.

Call for medical help immediately.Forster A, Palastanga N. Clayton’s Electrotherapy, Theory and Practice. 9th Ed. W B Saunders; 2006. p 50-54

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Electric shock, causes

Sudden increase in current during treatment

due to:

Machine switched don with controls up.

Sudden appearance of pulsed current with the

intensity high

Patient touching the machine


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Electric shock, precautions

The apparatus and the connections should be

tested before use

Controls should beat zero before switching on

Provide adequate warm up for equipment if

needed

Instruct the patient not to touch the apparatus

Service the apparatus regularly


Singh J. Text book of Electrotherapy. 2 edition. Jaypee. 2012. p 64

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Earth shock

When a shock is due to a connection between the live wire or earth it is known as an earth shock.

Connection to live wire can occur when

Wire is not properly insulated.

The live wire is not disconnected when the switch is put on neutral wire

Live wire touching metal casing

Live wire is touched to wet thing

Connection to live wire can occur when

Touching any conductor connected to earth

Metal casing on apparatus



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Earth shock, precautions

Proper arrangement of physiotherapy

department with insulating materials

Proper flooring with insulating materials and

kept dry

Patient should not touch the apparatus

Metal casing of all aparatus shold be

connected to earth

Use wooden furnishingsForster A, Palastanga N. Clayton’s Electrotherapy, Theory and Practice. 9th Ed. W B Saunders; 2006. p 50-54


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Thank You