Presentation on theme: "Ohm’s Law and Electric Shock. What causes a human body to be shocked…voltage or current? The electric current in amperes is the most important variable."— Presentation transcript:
What causes a human body to be shocked…voltage or current? The electric current in amperes is the most important variable which determines the severity of an electric shockelectric currentelectric shock
Will the 120 volt common household voltage produce a dangerous shock? It depends! If your body resistance is 100,000 ohms, then the current which would flow would be: But if you have just played a couple of sets of tennis, are sweaty and barefoot, then your resistance to ground might be as low as 1000 ohms. Then the current would be:
The severity of shock from a given source will depend upon its path through your body.
Bird on a wire A bird can sit on a high- voltage wire without harm, since both of its feet are at the same voltage. (There must be a difference in potential between one part of its body and another part.bird can sit on a high- voltage wire You can also see that the bird is not "grounded" – You will not be shocked by touching a high voltage if there is no path for the current to reach the Earth or a different voltage point.
The circuit is not completed Electricity always seeks the shortest, fastest path to an area of lower voltage. This path, or circuit, would only be completed if the bird was touching something other than the single wire. Otherwise, the current stays on its path through the line.
Larger Birds in Danger Larger birds sometimes complete the circuit when their wings touch another line or the pole. Once the circuit is completed, the electrical current flows through the bird to the area of lower voltage, resulting in electrocution.
Utility Worker Precautions Utility workers often work near damaged lines or in wet conditions where electrocution is possible. To protect themselves they use rubber gloves and boots (rubber is a poor conductor of electricity), insulated tools, and rubber mats and sheets to protect against exposed wire.
Why is the ground prong longer than the flat prongs? So it will be first to be plugged into a socket…thus a ground connection is established just before the appliance is electrically connected
Why do the two flat prongs on plugs for most electrical appliances have holes in them? If you unplug any appliance in your house, there is a 98 percent change that the two flat prongs have holes in them. There are three reasons for those holes. First, if you were to take apart an outlet, and look at the contact wipers that those prongs slide into, you would find that they have bumps on them. These bumps fit into the holes, so that the outlet can grip the plugs prongs more firmly. This prevents the plug from slipping out of the socket due to the weight of the plug in the cord. It also improves the contact between the plug and the outlet. Second, electrical devices can be factory sealed, or locked out, by the manufacturer or owner, using a plastic tie, or a small padlock that runs through one or both of those prong holes. For example, a manufacturer might apply a plastic band through the hole, and attach a tag to it that says ‘you must do blah, blah, blah, before plugging in this device’. The user can’t plug in the device without removing the tag, so the user is sure to see these instructions. Third, there is also a small savings in raw materials for the manufacturer of the actual plug prong. Every little bit helps.