 Voltages across series and parallel capacitive circuits. Welcome. In this video, we'll discuss voltages across series and parallel capacitive circuits. When a DC power source is connected across a capacitor, as shown in this illustration, the following conditions occur. First, the electrons from the negative terminal collect on the bottom plate of the capacitor. Second, as each electron collects on the bottom plate, it repels an electron from the top plate. Third, each electron that is repelled from the top plate flows to the positive terminal of the power source. As the capacitor is charging, the current flows as if there were a complete circuit. The current does not actually flow through the dielectric between the plates. Current flows until the charge on the plates causes a voltage to develop that's equal to the power supply. The current stops because there's no difference in potential. This means there's no difference in potential between the bottom terminal of the power source and the bottom plate of the capacitor. There's also no difference in potential between the top plate of the power source and the top plate of the capacitor. The size of the plates determines how many electrons need to collect on them to cause a given voltage to develop. A capacitor half the size of a second capacitor requires half the electrons to collect to cause an equal voltage to develop. Since the capacitor used in the circuit on the left has half of the electrons as the capacitor in the circuit on the right, its LED will be half as bright when it discharges. When capacitors are connected in parallel, a voltage equal to the power supply develops across each of them after the capacitors are completely charged. The three parallel 10 microfarad capacitors function as if they were one 30 microfarad capacitor. When the capacitors are connected in series, the same charge forms across all of them as they are being charged. This diagram shows how this occurs. As seen here, there's only one path for the current to flow. Each time one electron collects on the bottom plate of the capacitor, one electron from its top plate goes to the bottom plate of the top capacitor. Because the top plate receives its electrons from the bottom capacitor, it can't obtain more or fewer electrons. Therefore, it obtains the same number, and therefore the same charge develops across each one. When capacitors are connected in parallel, a voltage equal to the power supply develops across each of them after the capacitors are completely charged. When equal value capacitors are connected in series, the same voltage is dropped across each one. When unequal value capacitors are connected in series, the smallest voltage forms across the largest capacitor, and the largest voltage forms across the smallest capacitor. The larger voltage forms across the smallest size capacitor because the smaller capacitor has more dielectric. This means that the greater the dielectric, the more voltage that is required to develop an equal charge. Let's review. When two or more capacitors are connected in parallel across a DC power source, the voltage across them after they are fully charged is A equal or B not the same. The answer is A equal. When two or more unequal capacitors are connected in series with a DC power source, the charges that develop across them are A equal or B unequal. The answer is B unequal. Can you figure out the correct voltage for the capacitor shown in this image? The correct answers are 60 volts and 30 volts. Congratulations! You have completed watching the Voltage Across Series and Parallel Capacitive Circuits video.