Final answer:
The capacitor voltage at t = 0- is zero, and for t > 0, it increases according to V = emf(1 - e^-t/RC). The voltage approaches the emf value asymptotically as time progresses, and the rate of change is determined by the time constant τ = RC.
Step-by-step explanation:
To calculate the capacitor voltage at t = 0- (just before the switch is closed), we consider initial conditions of a typical RC circuit before it starts to charge. At this instant, the voltage across the capacitor is initially zero since it has not yet begun to charge. The instant after the switch is closed at t > 0, the charging of the capacitor begins, and the voltage across it starts to increase according to the equation V = emf(1 - e-t/RC), where emf represents the electromotive force of the power supply, R is the resistance, and C represents the capacitance.
Given that R = 4 Ω and we do not have the values for emf and C, we cannot provide a numerical value for the voltage at t > 0 without additional information. However, it is known that as time progresses, the voltage across the capacitor would approach the emf value asymptotically due to a decrease in charging current. This process is quantitatively described by the time constant τ (tau), which equals RC, and determines how quickly the voltage changes towards the emf value.