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An ohmmeter measures resistance by passing a small current through the resistor and measuring the voltage drop across it.

When an ohmmeter is connected to a resistor, it sends a small current through the resistor. The current is usually very small, typically around 1 mA, so as not to damage the resistor. The ohmmeter then measures the voltage drop across the resistor. Ohm's law states that the voltage drop across a resistor is directly proportional to the current passing through it and the resistance of the resistor. Therefore, by measuring the voltage drop and knowing the current, the ohmmeter can calculate the resistance of the resistor.

The ohmmeter is designed to measure resistance accurately, regardless of the voltage or current applied to the resistor. This is achieved by using a high-precision internal resistance, which is added in series with the resistor being measured. The internal resistance is then adjusted until the current passing through the resistor is constant and the voltage drop across the resistor is accurately measured.

In summary, an ohmmeter measures resistance by passing a small current through the resistor and measuring the voltage drop across it. The ohmmeter then uses Ohm's law to calculate the resistance of the resistor. The ohmmeter is designed to measure resistance accurately, regardless of the voltage or current applied to the resistor, by using a high-precision internal resistance.

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