Carbon resistors apply electrical resistance of known value to circuits.

The term mohm has several meanings depending on what the ‘m’ stands for. In some cases, om is a prefix used before –ohm , and means ‘mili-‘ or ‘mega-‘. Mohm can also be short for mobile ohm, a unit used to measure the mobility of sound waves.

When mohm refers to milliohm or megaohm, ohm is a mechanical ohm, which measures electrical resistance. In this context, resistance refers to how much a material opposes the flow of electric current. One ohm is equal to the amount of resistance incurred when 1 volt of electromotive force produces 1 Ampere of electrical current. A milliohm, written as mohm or mΩ, is one thousandth of an ohm, while a megaohm, written as Mohm or MΩ, is one million ohms.

Milliohms are the units of measurement used for objects of very low resistance. Milliohm meters can be used to test batteries, especially batteries for small electronic devices, which are designed to have low resistances. Batteries with lower resistance hold a charge longer as there is less force resisting the flow of current. The resistance of capacitors, devices that store electrical charge, is also often measured in milliohms, since capacitors with lower resistivity are more efficient.

Megaohms are used as units of measurement for objects with very high resistance. They are often used to test insulation, which must have a high resistance to minimize temperature changes in whatever is being insulated. The quality of distilled water is also measured in megaohms. Distilled water quality ranges from 1 to 18 megohms, with higher resistances indicating superior quality. The quality of distilled water is important in the manufacturing process of semiconductors and other electrical parts.

Moving ohms measure the mechanical mobility of sound waves. A moving ohm is the inverse of a mechanical ohm. In other words, one divided by the number of mechanical ohms gives the number of moving ohms. While a mechanical ohm measures resistance, a moving ohm measures the inverse of resistance, called conductance, so a higher measurement in moving ohms means that sound waves can move more easily.

Siemens is the most commonly used term for the measurement of conductance indicated by moving ohms. The unit was originally called mho – ohms spelled backwards – because it was the inverse of ohms, and mho is still sometimes used. Moving ohm or mohm is probably the least commonly used term for this measurement.