Transcript
Dr. Rashi Goel (PT)
Assistant Professor
DY Patil College of Physiotherapy
Pimpri, Pune
Definition
Use of electrical energy as a medical treatment
Electricity is an element of PT modalities most frightening and least understood
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Matter
Mass + occupies space Basic unit of matter- atom
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States of matter
Solid- lattice formation Liquid Gas
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Cohesive force- attracts molecules of the substance to one another
Kinetic force- force of movement of the molecules
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Properties of matter
Adhesion Surface tension Viscosity Density Elasticity
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Adhesion
Attachment of a substance to the surface of another substance
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Surface Tension
The cohesive forces between liquid molecules
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Viscosity
Quantity that describes a fluid's resistance to flow
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Density
Mass per unit volume
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Elasticity
Tendency of solid materials to return to their original shape after being deformed
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ATOM
A central nucleus surrounded by a cloud of electrons revolving in definite orbits
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Structure of atom
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Nucleus
Proton Neutron
Electron
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Molecule
Electrically neutral group of two or more atoms held together by chemical bonds
A substance that is the smallest particle of a compound and still contains all the characteristics of that compound
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Elements
a substance that is made entirely from one type of atom
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Compounds
Substance formed by the union of two or more elements, the union taking place via the electrons of the atoms involved to form a molecule of the compound
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Compounds
Covalent Electrovalent
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Molecule/Compound
A molecule is formed when two or more atoms join together chemically
A compound is a molecule that contains at least two different elements
All compounds are molecules but not all molecules are compounds
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Electron theory
Electric Charges:
Electrons have a –ve charge Protons- =+ve Neutrons- no charge
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An electrically neutral atom has the same number of protons and electrons
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Atomic no.= no. of protons in the nucleus
Atomic mass= no. of protons + no. of neutrons
Isotopes eg. Carbon
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Electricity
Electricity is the force created by an imbalance in the number of electrons at two points
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Static electricity
Simplest form of electricity
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Causes of static electricity
Static electricity is usually caused when certain materials are rubbed against each other, like wool on plastic or the soles of your shoes on the carpet
This causes electrons to be pulled from the surface of one material and relocated on the surface of the other material
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Try-
run a comb through your hair to charge the comb with static electricity
The comb can then be used to attract neutral pieces of tissue
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The material that loses electrons ends up with an excess of positive (+) charges
The material that gains electrons ends up an excess of negative (-) charges on its surface
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Electric field of a charged body
A zone of influence
Lines of force
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Properties of lines of force
I. Straight lines
II. Repel one another
III. Pass more easily through conductors than insulators
IV. Concentrate over that part of the surface over which they can exert an influence
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Electrical Potential
When compared to neutral potential of the earth
Unit- Volt High potential= strong repelling power
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Capacitance
The ability of tissue (or other material) to store electricity
Unit is Farad, microfarad
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Potential Difference
Difference in concentration of electrons between two points
Electrons will not move unless a potential difference exists
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EMF
Force producing the force
Electrons flow from more negative to less negative body until both are at same potential
Unit is Volts
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Current electricity
An electric current occurs when there is a flow of charged particles in a conductor
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Conductors
Materials that permit free movement of electrons
Composed of large numbers of free electrons
Offer little resistance to current flow Good conductors
Metals (copper, gold, silver, aluminum)Electrolyte Solutions
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Insulators
Materials that resist the flow of electrons Contain few free electrons Insulator materials
Air, Wood, Glass
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Electromagnetic Radiation
Produced by movement of electrons within the atom
Excited state
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Resistance
The opposition to flow of current
Measured in Ohms
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Intensity
Magnitude of current- rate of flow of electrons through the conductor per second
Measured in Amperes
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Ohm’s law
V = IR (V is voltage, a measure of the driving
force which is equal to the I x R where I is the Ampere (the amount of current flow) and R is the resistance
The Ampere is equal to the Voltage divided by the Resistance.
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Application of Ohm’s law to AC and DC currents Thermal effects of an electrical current
Joule’s law: Q= I2RT
I= current in amperes R= Resistance in ohms T= time in seconds
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Main supply
Produced by Dynamo Principal of Dynamo
Live wire- at high potential Neutral wire- at zero potential connected
to earth
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Electrical supply
Alternating sinusoidal current of 50 Hz at 220- 240 voltage
GRID SYSTEM
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Wiring in houses
Light and power circuits In parallel or in ring main Sub-circuits
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Numericals
2 formulae
EMF= VI V= IR
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Watt= 100W V= 240V R=?
Watt= 2000W V=240V R=?
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Results
1. I= 0.417A R= 576 ohm
2. I= 8.333A R=28.9ohm
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Over current/Excess current
A situation where a larger than intended electric current exists through a conductor, leading to excessive generation of heat, and the risk of fire or damage to equipment
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Causes for over current
Short circuits Excessive load Incorrect design
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Short Circuit
Resistance of circuit reduces- due to:
If insulation becomes worn out 2 supply wires come in contact Connection between live wire and earth
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Fuse
Weak point in the circuit which blows if a very high intensity of current is passed
Low melting point
Safety device
Live wire
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Fuse
Silver wire- fusible material Metal caps Glass tube Metal clips
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Cartridge fuse
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Why a fuse blows off?
1. Resistance too low
2. Wattage too high
3. Several parallel circuits from one supply point eg. Adaptors
To prevent overheating and fire
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When a fuse blows what to do?
1. Disconnect the apparatus
2. Switch off the main supply
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Dangers
Short circuits Electric shocks
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3 Pin Plug & Socket
Earth pin- longest
Live- brown Neutral- blue Earth- yellow and green
Easily distinguished
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One way to enter One way to exit
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Earthing
Precaution against earth shock
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Earth shock
Connection between live wire of the mains and earth
Earth circuit Eg.
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Precautions for earth shock
Water and gas pipes- out of reach of apparatus & patients getting treatment
Floor should be dry Floor of insulating material/mat placed Fuses on live wire
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Electric shock
Physiological reaction or injury caused by electric current passing through the human body
Painful stimulation of sensory nerves caused by a sudden flow, cessation or variation in the current passing through the body
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Causes of electric shock
Sudden increase in the current
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Effects of electric shock
Minor- frightened and distressed Major- Fall in BP, Loss of consciousness,
stoppage of respiration, cardiac arrest, ventricular fibrillation due to electrical stimulation of the heart
Death caused by an electric shock is called electrocution/ electrical execution
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Electrical currents flowing at <1mA will not be felt and is referred to as microshock
Shock from a current flow >1 mA is called macroshock
Currents b/w 1 - 15 mA: a tingling sensation or perhaps some muscle contraction
Currents b/w 15-100 mA: a painful electrical shock
Currents b/w 100 and 200 mA may result in fibrillation of cardiac muscle or respiratory arrest
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Severity of shock-
1. High voltage/ High current
2. Duration
3. Resistance of the body
4. Path taken by current- lethal if current flows through the heart muscle
5. Type of current
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Under dry conditions, resistance offered by the human body is- 100,000 Ohms
Wet or broken skin- body's resistance is 1,000 Ohms
high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms
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Treatment of electric shock
Disconnect the person from the source of supply
Switch off the current at once
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Precautions to be taken
Self test all equipments before using on patients
Check all connections Check all control knobs Intensity to be increased slowly Regular servicing of the equipments Patient should not touch electrical
equipments
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Electric shock as a medical therapy
Electroconvulsive therapy/ ECT- psychiatric illness
Defibrillation– for fibrillation/ irregular heart rhythms
For pain relief- TENS For hyperhidrosis- Iontophoresis
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