how a short circuit occurs
Did you ever see an old appliance with a damaged cord, like the old shown in the Figure 1.1? A damaged electric cord can cause a severe shock if it allows current to pass from the cord to a person who touches it. A damaged cord can also cause a short circuit. A short circuit occurs when electric current follows a shorter path than the intended loop of the circuit. An electric cord contains two wires: one that carries current from the outlet to the appliance and one that carries current from the appliance back to the outlet. If the two wires in a damaged cord come into contact with each other, current flows from one wire to the other and bypasses the appliance. This may cause the wires to overheat and start a fire.
electric safety features
Because electricity can be so dangerous, safety features are built into modern electric circuits and devices. They include three-prong plugs, circuit breakers, and GFCI outlets. You can read about these three safety features in the Figure 1.2. GFCI Outlet: GFCI stands for ground- fault circuit interrupter. GFCI outlets are typically found in bathrooms and kitchens where the use of water poses a risk of shock (because water is a good electric conductor). A GFCI outlet contains a device that monitors the amount of current leaving and returning to the outlet. If less current is returning than leaving, this means that current is escaping. When this occurs, a tiny circuit breaker in the outlet interrupts the circuit. The breaker can be reset by pushing a button on the outlet cover. Q: Can you think of any other electric safety features? A: One safety feature is the label on a lamp that warns the user of the maximum safe wattage for light bulbs. Another safety feature is double insulation on many electric devices. Not only are the electric wires insulated with a coating
using electricity safely
Even with electric safety features, electricity is still dangerous if it is misused. Follow the safety rules below to reduce the risk of injury or fire from electricity. Never mix electricity and water. Dont plug in or turn on electric lights or appliances when your hands are wet, you are standing in water, or you are in the shower or bathtub. The current could flow through the waterand youbecause water is a good conductor of electricity. Never overload circuits. Avoid plugging too many devices into one outlet or extension cord. The more devices that are plugged in, the more current the circuit carries. Too much current can overheat a circuit and start a fire. Never use devices with damaged cords or plugs. They can cause shocks, shorts, and fires. Never put anything except plugs into electric outlets. Putting any other object into an outlet is likely to cause a serious shock that could be fatal. Never go near fallen electric lines. They could have very high voltage. Report fallen lines to the electric company as soon as possible.
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electric current is dangerous because it can cause
a) electrocution. b) burns. c) fires. --> d) all of the above
why does the cord of an electric device contain two electric wires?
a) the two wires make up the two loops of a parallel circuit. b) one wire carries direct current and one wire carries alternating current. --> c) one wire carries current to the device and one wire carries current away from the device. d) two of the above
what is the purpose of the round prong on a three-prong plug?
--> a) it carries any stray electric current into the ground. b) it carries electric current to the appliance. c) it carries electric current away from the appliance. d) none of the above
you should never use electricity when you are wet or standing in water.
--> a. true b. false
overloading a circuit may cause it to have too much voltage.
a. true --> b. false
No diagram questions associated with this lesson