This effect may be used directly in electrical circuits. If a 9-volt battery is used, the LED would quickly burn out. However, if the appropriate resistor is added to the circuit, the voltage over the LED will be lowered. Lowering the voltage will prevent the LED from being damaged or destroyed. The resistor lowers the voltage in the entire circuit.
Resistors get hot when they are working because they exert control by converting power to heat.
They can only reduce the power of an electric signal, never increase it. The term ampere is the unit of electric current flow and is simply a measure of the rate at which electrons are flowing in a circuit. The pressure behind the electrons affects their rate of flow or amperes. The pressure, called voltage, is the electric pressure applied to electrons to make them flow. The volt is the common name or unit used to measure the electric pressure.