Final answer:
The force pulling free electrons toward the positive terminal in a circuit is referred to as voltage, influenced by the electric field and measured in volts (V).
Step-by-step explanation:
The force with which the positive terminal pulls the free electrons toward it in a circuit is essentially the influence of the electric field within the circuit, which is directly related to the electric potential difference, or voltage. This potential difference, when not in a complete circuit, is also known as electromotive force (emf) and is measured in volts (V). The work done by the electric field in moving electrons from the negative to the positive surface is done against an electric potential and is what constitutes voltage.
When a circuit is closed and current flows, the potential difference measured across the battery terminals is termed the terminal potential difference.
However, due to internal resistance (r), the actual measured voltage (V) is the emf minus the voltage drop due to the internal resistance and current (I), demonstrated in the equation V = emf - Ir. Here, the electric current is measured in amperes (A), a reflection of the charge flow rate.
Understanding current and voltage is crucial in determining the behavior and characteristics of an electric circuit, and the interaction between the electric field and the charges governs how the positive terminal attracts electrons.