LMS Substation 1st Year, Level II Practice Test

The correct choice highlights that the direction of the meter needle's deflection in an analog meter is essential for determining the polarity of the current when measuring DC current. In this context, an analog meter operates on the principle that the current flowing through it will cause the needle to deflect in a certain direction. If the current flows in the positive direction relative to the meter’s terminal connections, the needle will deflect towards one end of the scale, indicating one polarity. Conversely, if the current flows in the opposite direction, the needle will deflect in the opposite direction, indicating the other polarity. Thus, observing the needle's movement allows one to determine which direction the current is flowing and, consequently, its polarity.

While other factors such as the power source direction may provide context for understanding the circuit, they do not provide direct evidence of current polarity as the needle's movement does. Similarly, the color of the wires, while useful for visual identification of positive and negative connections, does not influence the measurement itself, nor does the voltage rating of the circuit directly relate to the actual measurement of current polarity.