After the capacitor is connected to the power supply, under the action of the electric field force, the free electrons of the capacitor plate connected to the positive pole of the power supply will move through the power supply to the plate connected to the negative pole of the power supply. The positive pole will be positively charged due to the loss of negative charge, and the negative pole will be negatively charged due to the gain of negative charge. The positive and negative plates will carry the same amount of charge, but the sign is opposite.

    The current is formed by the directional movement of charge. Due to the repulsive effect of the same charge, the current is the largest at the beginning and then gradually decreases. During the charge movement, the charge stored on the capacitor plate increases continuously. When the voltage UC between the two plates of the capacitor is equal to the power supply voltage U, the charge stops moving, the current I=0, the switch is closed, and the positive and negative plates of the capacitor are neutralized by the connection of the wire. When K is closed, the positive charge of capacitor C can be neutralized by moving to the negative electrode, and the negative charge of capacitor C can also be neutralized by moving to the positive electrode. The charge gradually decreases, indicating that the current decreases and the voltage gradually decreases to zero.