What will a voltmeter read if the positive terminal is connected to the negative terminal of the source voltage?

When a voltmeter is connected with its positive terminal to the negative terminal of a voltage source, it is measuring the potential difference in reverse. This configuration is referred to as being "backwards" or improperly connected. In this scenario, the voltmeter will still display a reading, but the sign of the reading will be negative, indicating that the polarity is reversed.

It's important to understand that voltmeters are designed to measure voltage difference between two points, and when connected correctly (positive to positive and negative to negative), they provide a positive reading. However, reversing the input connections causes the voltmeter to interpret the potential difference in the opposite direction, leading to the indication of "backwards" in the context of the measurement. Thus, the correct understanding of the voltmeter's operation under these conditions is that it will read backwards due to the reversed connection.