Ohmmeter is

Question

Ohmmeter is

Examoogle · Accepted Answer

Used to measure resistance

Explanation: An ohmmeter is an electrical instrument specifically designed to measure the electrical resistance of a component or a circuit. It functions by applying a small internal voltage to the component and measuring the resulting current flow, then displaying the resistance value based on Ohm's law.

Working Principle: The device typically contains an internal DC voltage source (battery) and a sensitive galvanometer or digital converter. When connected in series or parallel across an unknown resistance $R$, the current $I$ passing through the meter is inversely proportional to $R$ according to $I = \frac{V}{R+R_m}$. The meter scale is calibrated to read directly in ohms ($Omega$) rather than current.

Key Formulas: $R = \frac{V}{I}$ — Ohm's Law governing the measurement principle; $I = \frac{V_{battery}}{R_{total}}$ — Relationship between internal voltage and circuit resistance

Key Points: An ohmmeter must never be connected to a live circuit, as the external voltage can damage the internal meter components.; The component to be tested must be isolated from the rest of the circuit to ensure accurate readings.; Modern digital ohmmeters often provide high precision by using constant current sources instead of simple voltage dividers.

Advantages: Direct reading of electrical resistance.; Essential for testing continuity in wiring and PCB traces.

Disadvantages: Requires power source (battery) to operate.; Can be damaged by residual voltage in the component under test.

Applications: Checking continuity in electrical cables.; Measuring resistance of coils, heaters, and resistors.; Troubleshooting short circuits and open circuits.

Additional Info: Series-type ohmmeters are commonly used for high resistance measurements, while shunt-type ohmmeters are used for low resistance.. Option A and C are incorrect as they define the term etymologically rather than describing the function of the device.

Answer: B is correct — An ohmmeter is specifically engineered to measure electrical resistance in units of ohms.

Exam Tip: Always ensure the circuit under test is de-energized before using an ohmmeter to avoid incorrect readings and prevent internal damage to the instrument.

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