A student assembles a simple circuit consisting of a single ideal battery, a conducting switch, connecting wires of negligible resistance, and an identical incandescent bulb in two different configurations.
• Configuration 1: The switch is left open.
• Configuration 2: The switch is fully closed.
Assume the battery maintains a constant electromotive force (emf) ε and that the bulb’s resistance remains constant over the short time interval considered. Neglect thermal effects in the filament and assume the circuit reaches steady–state essentially instantaneously when the switch position changes.
(a) Describe the role played by the battery’s emf in establishing electric current in Configuration 2.
(b) Qualitatively explain why, in Configuration 1, no macroscopic current is measured even though mobile charge carriers are still present inside the wires.
(c) Immediately after the switch is opened while the bulb is glowing steadily, what happens to the average drift velocity of the conduction electrons in the section of wire nearest the switch? Justify your answer in terms of electric potential difference.