Final answer:
The voltage across the capacitor after the switch is closed is equal to the electromotive force (emf) of the circuit.
Step-by-step explanation:
In a circuit with a capacitor, as the switch is closed, the voltage across the capacitor increases over time until it reaches a maximum value. After the switch is closed for a long time, the capacitor is fully charged and the voltage across it reaches the maximum value, which is equal to the electromotive force (emf) of the circuit.
The voltage across the capacitor can be calculated using the formula V = emf(1 - e-t/RC), where V is the voltage across the capacitor, emf is the electromotive force, t is the time, R is the resistance in the circuit, and C is the capacitance of the capacitor.
Therefore, after the switch is closed for a long time, the voltage across the capacitor is equal to the electromotive force of the circuit.