Short Answer:

Resistance is measured using a multimeter by selecting the resistance (Ω) mode on the device and connecting the two probes across the component or part of the circuit where resistance is to be measured. The multimeter sends a small current from its internal battery through the component and measures the voltage drop to calculate resistance.

The value is then displayed directly on the screen in ohms (Ω). To get an accurate reading, the circuit must be powered off before measuring resistance, and the component should be isolated if possible to avoid false readings from parallel paths.

Detailed Explanation:

Resistance measurement using a multimeter

A multimeter is an essential instrument that can measure voltage, current, and resistance. When used for measuring resistance, it works by using its internal battery to apply a small known voltage across the component and then measuring the resulting current. Using Ohm’s Law (R = V/I), the multimeter calculates and displays the resistance directly on the screen.

Resistance is measured in ohms (Ω), and the multimeter shows the result in ohms, kilo-ohms (kΩ), or mega-ohms (MΩ), depending on the value. Measuring resistance is useful for checking the condition of resistors, wires, or any electrical path to see if it is open, shorted, or within the expected range.

Step-by-step Process to Measure Resistance:

Turn Off the Power:
Before measuring resistance, ensure that the circuit or component is not connected to any power source. Resistance measurement involves applying a small voltage from the multimeter itself, so any external voltage can damage the device or give false readings.
Select Resistance Mode (Ω):
Set the multimeter’s function switch to the resistance mode, usually marked with the omega (Ω) symbol. In auto-ranging meters, the device sets the range automatically. In manual meters, select the appropriate range based on the expected resistance value.
Connect the Probes:
- Insert the black probe into the COM (common) port.
- Insert the red probe into the port labeled with an ohm (Ω) symbol.
Connect to the Component:
Touch the metal tips of the probes to the two ends of the resistor or component. Ensure good contact for accurate results. Avoid touching the metal tips with your fingers, as body resistance can affect the reading.
Read the Display:
The multimeter will display the resistance value on the screen. If the reading shows OL (Over Limit), it means the resistance is beyond the selected range or the component is open (infinite resistance).
Adjust the Range (if needed):
If using a manual range multimeter, adjust to a higher or lower range for a clearer reading. Auto-ranging meters do this automatically.

Important Tips for Accurate Measurement:

Disconnect the component from the circuit if possible to avoid parallel resistance paths.
Wait a few seconds for the reading to stabilize, especially in high-resistance measurements.
Zero the meter (if it has this function) to cancel out any probe or internal resistance.
Ensure probes are clean and firmly connected.

Applications:

Checking if a resistor matches its labeled value.
Testing wire continuity by checking if resistance is near zero.
Verifying if a switch or connection is open or closed.
Diagnosing faults in electronic and electrical circuits.

Conclusion

Resistance is measured with a multimeter by applying a small internal voltage and sensing the current to calculate the value. This process is safe and reliable if the circuit is turned off and proper contact is made. Measuring resistance helps in identifying faulty components, broken wires, or incorrect values in a circuit, making it an essential function in troubleshooting and testing.