Capacitor discharge process
The discharge process is the process of discharging the stored charge by the capacitor. When the charging capacitor is in a closed path without a power source, the charge on the negatively charged metal plate will be positively charged under the action of the electric field force. The circuit board is removed, the positive and negative charges are neutralized, and the capacitor begins to discharge.
In the circuit, the movement of charge forms a current. Due to the attraction of the opposite charge, the current is maximum at the beginning of the discharge process and then gradually decreases. The charge of the capacitor is maximum at the beginning of the discharge process, and then gradually decreases. When the charge is reduced to zero, the discharge is completed and the current is reduced to zero.
Since no current flows in the circuit after the capacitor is charged, the capacitor can be used as a DC blocking circuit. In a DC circuit, it can be regarded as an open circuit.
Characteristics and laws of capacitor charging and discharging
According to the data and curves of the UC and IC when charging and discharging the capacitor obtained above, many very practical laws can be summarized.
1. It takes time to charge and discharge the capacitor. This is due to the charging and discharging process of the capacitor, which is basically the process of accumulating and dissipating the charge on the capacitor. Since the change of the charging amount takes time, it takes time to charge and discharge.
2. At the beginning of charging, the charging current is large and u rises faster. As the increase increases, the charging current gradually decreases, u rises slowly, and is close to the power supply voltage E. In theory, in order to completely complete the capacitor, the entire charging process is infinitely long. However, it can be seen that at t=15s, u=9.5V, which has reached 95% of E; at t=25s, u=9.93V, in fact, it can be considered that the capacitor is basically full, and the charging process is basically End.
Similarly, at the beginning of discharge, the voltage UC and current IC change faster, and then become slower. When t=15s, u=0.5V, only 5% E; when t=25s, u=0.07V, it can be considered that the charge of the capacitor is basically discharged, and the discharge process is completed.
In summary, when analyzing actual problems, it can be considered that the time required for the charging and discharging process of the capacitor is limited. That is to say, for the above experimental circuit, the capacitor self-charges and discharges from 15s to 25s. From an engineering point of view, it can be considered that charging and discharging have ended.
3. When the capacitor has just started to charge or just started to discharge, the terminal voltage of the capacitor and the stored charge Q will maintain the value before the start of charging and discharging. For example, if the voltage of the capacitor before charging is u=0V, the UC at the start of charging remains at 0V; if u=E of the capacitor before discharging, the discharge starts at E. That is, the terminal voltage of the capacitor at the beginning of charging and discharging u will not suddenly become large, this characteristic of the capacitor is very important and must be remembered.
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