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ELECTRIC CURRENT AND ITS EFFECTS

ELECTRIC CURRENT AND ITS EFFECTS. ELECTRIC CHARGE AND CURRENT VOLTAGE, CURRENT, RESISTANCE MATERIALS DIRECT CURRENT AND ALTERNATING CURRENT CURRENT EFFECTS IN HUMAN BODY SAFETY AND FIRST AID. CHARGE AND CURRENT. THE MASS IS ELECTRICALLY NEUTRAL. atoms can lose and accept electrons

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ELECTRIC CURRENT AND ITS EFFECTS

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  1. ELECTRIC CURRENT AND ITS EFFECTS ELECTRIC CHARGE AND CURRENT VOLTAGE, CURRENT, RESISTANCE MATERIALS DIRECT CURRENT AND ALTERNATING CURRENT CURRENT EFFECTS IN HUMAN BODY SAFETY AND FIRST AID

  2. CHARGE AND CURRENT • THE MASS IS ELECTRICALLY NEUTRAL • atoms can lose and accept electrons • elementary charge = - 1,6021892 . 10-19 C ELECTRIC CURRENT IS THE MOVEMENT OF CHARGE ampere – A; coulomb – C; second - s

  3. DIRECT CURRENT - DC • CHARACTERISTICS: • sense of current flow is constant • CONVENTION: • positive sense is from + to - Instantaneous value i(ti) Mean value I

  4. ALTERNATING CURRENT - AC • CHARACTERISTICS: • sense of current flow changes • mean value during T = zero • changes repeat periodically • CONVENTION: • positive sense is from + to - Instantaneous value i(ti ) Peak value (amplitude) Imax RMS (root-mean-square) value I

  5. MEAN VALUES - average hertz – Hz; second - s

  6. MEAN VALUES – equivalent DC hertz – Hz; second - s

  7. MEAN VALUES – harmonic current hertz – Hz; second – s

  8. RMS VALUES

  9. VOLTAGE,CURRENT,RESISTANCE (W;Wm,m,m2) r = resistivity (also in Wcm or Wmm2/m) TCR = temperature coefficient (former a) voltage U – volt – V current I – ampere – A resistance R – ohm – W

  10. MATERIALS ACCORDING TO FREE CHARGES TRANSFER: CONTUCTORS – r = 10-4 to 10 m Mostly used = metals. With increasing J rises R. SEMI-CONDUCTORS – r = 10 to 1010m Several chemical compounds and elements - Se, Ge, Si. With increasing J decreases R. INSULANTS(dielectric) – r > 1010m Ideal = vacuum. In industry for example mica, glass, silk, transformer oil, nitrogen etc.

  11. EFFECTS OF CURRENT THERMIC LIGHTING CHEMICAL MAGNETIC FORCE PHYSIOLOGICAL COOKERS TUBES ELECTROLYSIS COILS MOTORS THERAPY

  12. PHYSIOLOGICAL EFFETCS • Effects of current flow through living organism, especially human body. • Medical treatment • Electric current accidents • DC current • decomposes body cells, • causes heavy body burns, • can also harm heart activity. AC current – depends on frequency – 50 to 60 Hz causes muscle contraction and heart spasm.

  13. ACCIDENTS HAZARD IS ALWAYS CAUSED BY CURRENT • FACTORS: touch voltage and environment conditions • time of duration • body resistance – over skin 1000 - 3000 W Treshold of perception: 1 – 3 mA, let-go limit: 10 mA, fibrillation limit: 35 mA • FREQUENT ACCIDENTS: shock • burns • cramps • stopped breathing • stopped heart activity

  14. PROTECTION KNOWLEDGE (rules, standards …) and CAUTION INJURY IS NOT CAUSED BY: Safe current (according ČSN IEC 479 (33 2010)) PERMISSIBLE TOUCH VOLTAGE ČSN 33 2000-4-41 (usual condition – DC 120 V, AC 50 V permanent) TECHNICAL MEASURES: INSULATION PROTECTIVE MEANS CONNECTION, CONSTRUCTION, PLACEMENT

  15. BASIC FIRST AID • SET AFFLICTED PERSON FROM THE RANGE OF CURRENT • TREATMENT OF SECONDARY INJURIES • ARTIFICIAL RESPIRATION • INDIRECT HEART MASSAGE ALWAYS CALL DOCTOR RENDER FIRST AID TREATMENT TILL THE DOCTOR COMES

  16. Example 1a signal generator measuting instrument osc. • SINE WAVE CURRENT • FIND PEAK VALUE • MEASURE RMS VALUE • ? RELATION BETWEEN PEAK AND RMS VALUES • ?INFLUENCE OF FREQUENCY

  17. Example 1b • RECTANGULAR WAVE CURRENT • FIND MEAN VALUE • FIND RMS VALUE • ? EFFECT OF THE FORM OF RECTANGLE

  18. Example 1c • RECTANGULAR CURRENT WITH DC OFFSET • FIND MEAN VALUE • FIND RMS VALUE • ? ARE THERE SOME DIFFERENCES IN VALUES CALCULATED BY MEANS OF DISCUSSED EQUATIONS

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