Resistors are electronic components used to control the flow of electrical current in a circuit. They are an essential component of all electronic systems, and can be found in everything from mobile phones and computers to household appliances and automobiles. Resistors come in many shapes and sizes, and each type has unique characteristics that determine its purpose and application. Commonly, resistors are characterized by their resistance value, tolerance, power rating, temperature coefficient, and maximum voltage. Resistance, measured in ohms (Ω), is the ratio of voltage applied to current that flows. Tolerance is the amount of variation from the specified resistance value allowed, and power rating is the maximum amount of electrical power that a resistor can safely dissipate. Lastly, temperature coefficient is the amount the resistance will change with changes in temperature, and maximum voltage is the maximum amount of voltage the resistor can withstand before breaking down.