Final answer:
Increasing the distance between the voltmeter and the electric field source would weaken the electric field strength, as the electric field is inversely proportional to distance.
Step-by-step explanation:
The student's question asks which option would weaken the electric field as measured by a voltmeter. In this scenario, the correct answer is A. Increasing the distance between the voltmeter and the electric field source. The electric field (E) between two points is directly related to the potential difference (V) and inversely related to the distance (d) between these points. The relationship can be expressed as E = V/d, which indicates that the electric field strength is proportional to the potential difference and inversely proportional to the distance. Therefore, increasing the distance while keeping the voltage constant would result in a decreased electric field strength. Conversely, options B, C, and D do not directly weaken the electric field measured by a voltmeter.