Final answer:
The direction of conventional current through a voltmeter can determine the type of charge carriers in a conductor. For positive charge carriers, the direction is downward, and for negative charge carriers like electrons, it is upward. This is because conventional current is taken to flow in the direction a positive charge would move.
Step-by-step explanation:
When dealing with circuits and the movement of charge, it is important to understand the concept of conventional current, which is defined as the direction a positive charge would flow. From this standpoint, if the internal resistance of the voltmeter is less than infinity and the meter is connected such that it reads a positive voltage, it indicates a higher potential at the positive terminal relative to the negative terminal. Therefore, for a wire carrying positive charge carriers (holes), an upward current through the voltmeter would denote a positive voltage if the contact point p1 is higher than p2.
Conversely, if electrons are the charge carriers, the actual current (flow of electrons) is opposite to the direction of the conventional current. Hence, an upward current through the voltmeter would signify a negative voltage if the voltmeter is connected with p1 above p2, given that electrons move from the lower potential to the higher potential area. Thus, the direction of current through the voltmeter would be downward for positive charge carriers and upward for negative charge carriers, as in option 4.
In summation, by measuring the sign of the voltage V and knowing the direction of the conventional current, it's possible to determine the sign of the majority charge carriers within the metal. This is based on the convention set forth by Benjamin Franklin, who defined a positive current moving to the right as the same as a negative current of equal magnitude moving to the left.