The capacitor charges up, through the 470 kΩ k Ω resistor. No current flows through the PUT, because it's off. So, no current flows through the LED, either. Because the current through the capacitor is small, its voltage grows, but slowly. Eventually, the capacitor reaches the threshold voltage to turn on the PUT. It turns on.
Initially, the current is high, as the capacitor acts like a short circuit, allowing the flow of current to build up the charge on its plates. However, as the capacitor charges and the voltage across it increases, the potential difference between the capacitor and the source decreases, resulting in a decrease in current flow.
Discharging a capacitor into a fixed resistance creates another exponential curve, this time reducing toward zero. The discharge current is a negative value because of the reversal of current flow. The charge flows out of the capacitor.
At first glance, capacitors may seem like insulators due to their ability to store charge. Yet, they are not entirely impervious to the flow of electric current. While it is true that capacitors block direct current (DC), they do allow for the flow of alternating current (AC).
If a time-varying voltage is applied across the leads of the capacitor, the source experiences an ongoing current due to the charging and discharging cycles of the capacitor. However, no current actually flows through the dielectric itself.
As a result, the capacitor is charged, which means that there is flow of charge through the source circuit . If a time-varying voltage is applied across the leads of the capacitor, the source experiences an ongoing current due to the charging and discharging cycles of the capacitor.