However, electrons do not pass through the dielectric of the capacitor. As the applied AC voltage increases and decreases in amplitude, the capacitor charges and discharges. • The resulting movement of electrons from one plate of the capacitor to the other represents cur- rent flow. • In a pure resistive circuit, the current flows in phase with the applied voltage. Current and voltage in a capacitive AC circuit do not flow in phase with each other This relationship is described as 90° out of phase. The current leads the applied voltage in a capacitive circuit.
In a capacitive AC circuit, the applied voltage is constantly changing, causing the capacitor to charge and discharge. After the capacitor is initially charged, the voltage stored on its plates opposes any change in the applied voltage. The opposition that the capacitor offers to the applied AC voltage is called capacitive reactance . Capacitive reactance is represented by X C and is measured in ohms.
APPLICATIONS OF CAPACITIVE CIRCUIT • A filter is a circuit that discriminates among frequencies, attenuating (weakening) some while allowing others to pass. • It works by establishing a cutoff point between frequencies that are passed and frequencies that are attenuated. • The two most common types of filters are low-pass filters and high-pass filters . • A low-pass filter allows low frequencies to pass with little opposition while attenuating the high frequencies. • A high-pass filter permits frequencies above the cutoff point to pass while attenuating frequencies below the cutoff point.
RC LOW PASS FILTER • A low-pass filter consists of a capaci- tor and a resistor in series. The input voltage is applied across both capacitor and resistor. • The output is taken from across the capacitor. • At low frequencies, the capaci- tive reactance is higher than the resistance, so most of the voltage is dropped across the capacitor. • Therefore, most of the voltage appears across the output. As the input frequency increases, the capacitive reactance decreases, and less voltage is dropped across the capacitor. • There- fore, more voltage is dropped across the resistor, with a decrease in the output voltage. The cutoff is gradual. • Frequencies above the cutoff point pass with a gradual attenuation in the output voltage.
RC HIGH PASS FILTER • A high-pass filter also consists of a resistor and capacitor in series. • However, the output is taken across the resistor.
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- Winter '18
- Alternating Current, Inductor, Electrical resistance, Low-pass filter, ac circuit