Meter Sensitivity Explained

Understanding the sensitivity of an electrical meter is crucial in electrical measurements. A meter's sensitivity indicates how much current is required to produce a full-scale deflection (FSD). Essentially, the less current a meter needs to achieve full-scale deflection, the more sensitive it is. A highly sensitive meter can detect smaller changes in the measured quantity.

Sensitivity Definition and Formula

The sensitivity of a meter is generally defined as the reciprocal of the current required for full-scale deflection. While often expressed in ohms per volt ($\Omega/\text{V}$) for voltmeters, in the context of comparing ammeters or galvanometers based on their full-scale deflection current, a meter is considered more sensitive if it requires a smaller current for full-scale deflection.

Mathematically, if sensitivity is inversely proportional to the full-scale deflection current ($\text{I}_{\text{FSD}}$), we can express it as:

$\text{Sensitivity} \propto \frac{1}{\text{I}_{\text{FSD}}}$

This relationship implies that a lower full-scale deflection current ($\text{I}_{\text{FSD}}$) corresponds to higher meter sensitivity.

Analyzing Meter Deflection Currents

Let's examine the full-scale deflection (FSD) current requirements for each given meter:

• Meter A requires $\text{100 mA}$ to give full-scale deflection.
• Meter B requires $\text{50 mA}$ to give full-scale deflection.
• Meter C requires $\text{80 mA}$ to give full-scale deflection.

Comparing Meter Sensitivity

To determine which meter is more sensitive, we must compare the full-scale deflection currents for each meter. As established, the meter that requires the least amount of current to achieve full-scale deflection is the most sensitive meter.

From the comparison of the currents required for full-scale deflection:

• Meter A needs the highest current of $\text{100 mA}$.
• Meter B needs the lowest current of $\text{50 mA}$.
• Meter C needs an intermediate current of $\text{80 mA}$.

Since $\text{50 mA}$ is the smallest current required for full-scale deflection among the three meters, Meter B exhibits the highest sensitivity.

Conclusion on Meter Sensitivity

Based on the analysis of the full-scale deflection current for each meter, Meter B requires the least current ($\text{50 mA}$) to achieve full-scale deflection. This makes Meter B the most sensitive among Meter A ($\text{100 mA}$) and Meter C ($\text{80 mA}$). Therefore, Meter B is more sensitive.