Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Lecture Notes Human Body Electric Shock

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Physics: To show the fundamental laws applied in a ground fault circuit interrupter (GFCI). Biology: To understand the effect of electrical current on the human body. Electric Shock Goals

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Physics: Ohms law determines current flow through a resistor. Electromagnetic induction can be used to prevent electrical shocks. Biology: Human body acts like a resistor. Electrical currents interfere with nerve impulses. This affects muscle contraction, heart functioning and breathing. Burns can also occur. Electric Shock Big Ideas

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Human body acts like a resistor. V =IR Electric Shock Human body Dry skin 1 : R = kΩ Wet skin 1 : R ~ 1 kΩ Inside body 1 : Water and electrolytes. Each limb has R = ~ 500Ω Rubber shoes 2 : R = 20MΩ Leather shoes, dry 2, R = kΩ Leather shoes, wet 2, R = 5 – 20 kΩ Total resistance depends on path of current.

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Electric Shock Electric shock Effect of current on body (60 Hz AC) 1 : 0-1 mA Imperceptible 1-3 mA Perceptible, mild 3-5 mA Annoyance 6-9 mA Muscles contract and cannot let-go 30 mA Asphyxiation 80 mA Ventricular fibrillation 5-10 A Cardiac arrest, burns Duration of exposure important as well.

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Electric Shock GFCIs Ground fault circuit interrupters (GFCIs) are installed in power outlets in wet environments such as bathrooms, kitchens, outside, pools etc. They sense the development of an imbalance in the current going out of the outlet and the current returning to the outlet. They will shut off the current flow if an imbalance is sensed.

Electric Shock GFCIs cont’d The development of an imbalance in current will cause a change in the B- field inside the sense coil. A change in magnetic flux induces a voltage activates electronics which stops the current flow.

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Designed to shut off in 7.5 s for a 5 mA imbalance and within 25 ms for greater than a 264 mA imbalance 3. The duration of shock is limited, not the amount of current. GFCIs do not protect against touching the hot and neutral wires. Electric Shock GFCIs cont’d

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia [1] Magison, E.C., Electrical instruments in hazardous locations 3 rd ed., Instrument Society of America (1972) [2] hpt_3/3.htmlhttp:// hpt_3/3.html [3] Quick, R. C., IEEE Transactions on Industry Applications, Vol IA-11, No. 1 January/February 1975 Electric Shock References