Without modification, plugs on cords made for 220 volt appliances won't fit into 110 volt outlets. Receptacles for 220 volts are different than receptacles for 110 volts. The reverse is also true. Standard plugs and receptacles exist for both voltages and manufacturers are required to adhere to those standards in order to pass safety testing.
Attempting to operate an appliance at anything but the voltage range specified on the appliance's nameplate won't work in most cases. If it does work, the appliance will probably operate at a higher temperature than normal since it will require twice the current to make up for the low voltage.
Relationship Between Voltage, Current and Power
Any appliance that uses electricity requires a certain amount of power to do the work it was designed to do. Power has two components -- voltage and current -- and is expressed by the equation P = V x I where P is power in watts, V is voltage and I is current in amperes.
By this formula, an appliance that requires 2200 watts of power uses 20 amperes of current at 110 volts and 10 amperes of current at 220 volts. If this appliance is plugged into a standard 15 amp, 110 volt outlet, it will attempt to draw 20 amperes of current and the circuit breaker will trip or the fuse will blow.
Electric motors in particular are sensitive to the voltage supplied to them. Many appliances from refrigerators to vacuum cleaners to hair dryers contain electric motors. The motors in these appliances will run very slowly, if they start at all, and will get quite hot. This may not cause an issue in the beginning, but it will cause the motor to burn out prematurely.
Most manufacturers are clear about specifying warranties. They design the product to operate under a given set of conditions, including the voltage supply to the appliance. If you or anyone else modifies the appliance so it will plug into a different voltage than that specified, the warranty will likely be voided.
Dual Voltage Appliances
Manufacturers design some appliances to run on two voltage ranges and supply appropriate cords or plugs for both circumstances. For example, personal computers may have a switch on the back that allows the computer to use either 110 to 125 volts or 220 to 250 volts.
The switch changes how the power supply within the computer acts on the current supplied to it. The output of the power supply remains the same and computer operates just fine. As shown previously, the computer will use twice as much current at 110 volts than it does at 220, but since the current draw is low this does not present a problem.