Question

question 19

in a one-terminal zero-center voltmeter connected to ground and the probe connected to a point a, the pointer of the voltmeter gives a ______ for voltage.
a. positive
b. stabilizing
c. negative
d. neutralizing

Explanation:

Analyze the voltmeter connection

Using the Voltmeter Measurement and Ground Reference knowledge points

A zero-center voltmeter can deflect both left and right from its central zero position to indicate polarity. When the reference terminal of the voltmeter is connected to ground (\(0\text{ V}\)) and the measurement probe is connected to a Point A, the meter measures the potential of Point A relative to ground:

$$ V_{\text{measured}} = V_A - V_{\text{ground}} = V_A - 0 = V_A $$

Determine the sign of the reading

Using the Voltmeter Measurement knowledge point

If Point A is at a potential below ground (negative potential), the potential difference \(V_A - V_{\text{ground}}\) is negative. This negative potential difference causes the pointer of the zero-center voltmeter to deflect to the negative side of the scale, giving a negative reading for voltage.

Evaluate the given options

Using the Voltmeter Measurement knowledge point

• a. positive: Occurs if Point A is at a higher potential than ground.
• b. stabilizing: Not a standard term for directional voltage indication.
• c. negative: Correctly describes the indication when Point A is negative relative to ground.
• d. neutralizing: Not a standard term for directional voltage indication.

Answer:

• a. positive
• b. stabilizing
• c. negative (Correct answer)
• d. neutralizing