the modern home has electrical circuits supplying energy to many electrical appliances the lead in wires connected to a main switch from the switch wires lead to a meter which records the amount of electrical energy used and then do a fuse box from which branch lines lead to all parts of the house each branch with two wires and in a service outlet an appliance such as this lamp with a plug completes the circuit molecular appliances such as electric range electric roaster and many others depend on the fact that electricity produces much heat as it passes through certain substances these iron illustrates the principle of the common electrical heating appliance this pressure plate holds the heating element firmly in place sheets of mica separate this heating element from the metal of the iron mike and as an insulator and does not easily conduct electricity the actual heating is produced in this resistance wire in this iron the resistance wire is wound around a sheet of mica the passage of electrons through the resistance wire produces heat this heat is transmitted to the base of the iron the motion of the electrons is a representation of an alternating current over heating or dropping an electric iron may cause damage to the heating unit if the damage is in the resistance wire or in the insulating material the iron can be restored to us from this by inserting a new heating unit many modern irons include a temperature controlling device called  the principle of the thermostat mechanism is shown by this animated drawing at the top business trip consisting of two metals welded together as the iron cools the strip again straightens out and makes contact electrons flow through the circuit as this iron heats the lower metal of the strip expands more than the upper metal this causes the script to band and again break the contact no electrons c and the iron cools this alternate closing and opening of the circuit maintains a nearly constant temperature this action of a by a metal strip is the principle of most household t lamp uses a resistance wire to produce light the intensity of the light produced by the heated filament depends upon the length the size and the material of which the wire is more economical because more of the energy is converted into light which starts the action when the lamp is turned on some electrons flow across the gap in the globe of the heat from this arc causes a bi metal strip to make contact eliminating the arc many electrons now flow through the metallic circuit heating the filaments in the fluorescent bulb the bimetal strip cools bands and opens the upper circuit at that instant electrons given off but the heat had with the mercury molecules causing the molecules to give off invisible ultraviolet radiation and called light electricity is also used to operate motors as in the washing machine in the dishwasher in the electric mixer and in many other appliances of everyday convene of course all of these motor appliances involve other physical principles besides electricity the vacuum cleaner is one of the common home appliances driven by a motor the fan which draws the dirt into the cleaner bag is connected directly to the motor this armature connects with the electric circuit by means of graphite rods called brus if these brushes become worn down replacement is easily made by unscrewing the cap over the spring which holds the brush in position the worn brush is then removed from the spring and a new brush is inserted the common type of electric refrigerator also depends upon the use of a motor liquid by compression compressor pump driven by the motor goes the gas molecules from the evaporator above and forces them into the condenser that's compressing the gas in the condenser heat is withdrawn a fan also driven by the electric motor is sometimes used to carry away this heat here we see the compressor bump but here is a condenser with a fan in back of it the liquid is forced into the evaporator through a needle valve here under reduced pressure the liquid evaporates and becomes a gas in this process heat is withdrawn from the freezing compartment the pump again draws the gas from the evaporator and forces it into the condenser where it again liquefy is and the cycle begins again as a result of heat being withdrawn from the freezing compartment convection currents are set up in the air within the refrigerator cold air is heavier than warm air temps the cold air moves downward from the freezing compartment towards the bottom of the refrigerator the air which has been warmed by heat taken up from the food it's forced upwards this warmer air comes in contact with the freezing unit is cooling and the circulation construction and economy of operations why is election and proper maintenance well it's your long life of operating usefulness